License cleanup: add SPDX GPL-2.0 license identifier to files with no license
Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.
By default all files without license information are under the default
license of the kernel, which is GPL version 2.
Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier. The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.
This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.
How this work was done:
Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
- file had no licensing information it it.
- file was a */uapi/* one with no licensing information in it,
- file was a */uapi/* one with existing licensing information,
Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.
The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne. Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.
The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed. Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.
Criteria used to select files for SPDX license identifier tagging was:
- Files considered eligible had to be source code files.
- Make and config files were included as candidates if they contained >5
lines of source
- File already had some variant of a license header in it (even if <5
lines).
All documentation files were explicitly excluded.
The following heuristics were used to determine which SPDX license
identifiers to apply.
- when both scanners couldn't find any license traces, file was
considered to have no license information in it, and the top level
COPYING file license applied.
For non */uapi/* files that summary was:
SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 11139
and resulted in the first patch in this series.
If that file was a */uapi/* path one, it was "GPL-2.0 WITH
Linux-syscall-note" otherwise it was "GPL-2.0". Results of that was:
SPDX license identifier # files
---------------------------------------------------|-------
GPL-2.0 WITH Linux-syscall-note 930
and resulted in the second patch in this series.
- if a file had some form of licensing information in it, and was one
of the */uapi/* ones, it was denoted with the Linux-syscall-note if
any GPL family license was found in the file or had no licensing in
it (per prior point). Results summary:
SPDX license identifier # files
---------------------------------------------------|------
GPL-2.0 WITH Linux-syscall-note 270
GPL-2.0+ WITH Linux-syscall-note 169
((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause) 21
((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) 17
LGPL-2.1+ WITH Linux-syscall-note 15
GPL-1.0+ WITH Linux-syscall-note 14
((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause) 5
LGPL-2.0+ WITH Linux-syscall-note 4
LGPL-2.1 WITH Linux-syscall-note 3
((GPL-2.0 WITH Linux-syscall-note) OR MIT) 3
((GPL-2.0 WITH Linux-syscall-note) AND MIT) 1
and that resulted in the third patch in this series.
- when the two scanners agreed on the detected license(s), that became
the concluded license(s).
- when there was disagreement between the two scanners (one detected a
license but the other didn't, or they both detected different
licenses) a manual inspection of the file occurred.
- In most cases a manual inspection of the information in the file
resulted in a clear resolution of the license that should apply (and
which scanner probably needed to revisit its heuristics).
- When it was not immediately clear, the license identifier was
confirmed with lawyers working with the Linux Foundation.
- If there was any question as to the appropriate license identifier,
the file was flagged for further research and to be revisited later
in time.
In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.
Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights. The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.
Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.
In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.
Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
- a full scancode scan run, collecting the matched texts, detected
license ids and scores
- reviewing anything where there was a license detected (about 500+
files) to ensure that the applied SPDX license was correct
- reviewing anything where there was no detection but the patch license
was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
SPDX license was correct
This produced a worksheet with 20 files needing minor correction. This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.
These .csv files were then reviewed by Greg. Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected. This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.) Finally Greg ran the script using the .csv files to
generate the patches.
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2017-11-01 14:07:57 +00:00
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/* SPDX-License-Identifier: GPL-2.0 */
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2005-04-16 22:20:36 +00:00
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#ifndef _LINUX_STRING_H_
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#define _LINUX_STRING_H_
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#include <linux/compiler.h> /* for inline */
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#include <linux/types.h> /* for size_t */
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#include <linux/stddef.h> /* for NULL */
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2009-03-06 16:21:46 +00:00
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#include <stdarg.h>
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2012-10-13 09:46:48 +00:00
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#include <uapi/linux/string.h>
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2005-04-16 22:20:36 +00:00
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2006-03-24 11:18:42 +00:00
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extern char *strndup_user(const char __user *, long);
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2009-03-31 22:23:16 +00:00
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extern void *memdup_user(const void __user *, size_t);
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2018-01-07 18:06:15 +00:00
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extern void *vmemdup_user(const void __user *, size_t);
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2015-12-24 05:06:05 +00:00
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extern void *memdup_user_nul(const void __user *, size_t);
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2006-03-24 11:18:42 +00:00
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2005-04-16 22:20:36 +00:00
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/*
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* Include machine specific inline routines
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*/
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#include <asm/string.h>
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#ifndef __HAVE_ARCH_STRCPY
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extern char * strcpy(char *,const char *);
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#endif
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#ifndef __HAVE_ARCH_STRNCPY
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extern char * strncpy(char *,const char *, __kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_STRLCPY
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size_t strlcpy(char *, const char *, size_t);
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#endif
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2015-04-29 16:52:04 +00:00
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#ifndef __HAVE_ARCH_STRSCPY
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string: drop __must_check from strscpy() and restore strscpy() usages in cgroup
e7fd37ba1217 ("cgroup: avoid copying strings longer than the buffers")
converted possibly unsafe strncpy() usages in cgroup to strscpy().
However, although the callsites are completely fine with truncated
copied, because strscpy() is marked __must_check, it led to the
following warnings.
kernel/cgroup/cgroup.c: In function ‘cgroup_file_name’:
kernel/cgroup/cgroup.c:1400:10: warning: ignoring return value of ‘strscpy’, declared with attribute warn_unused_result [-Wunused-result]
strscpy(buf, cft->name, CGROUP_FILE_NAME_MAX);
^
To avoid the warnings, 50034ed49645 ("cgroup: use strlcpy() instead of
strscpy() to avoid spurious warning") switched them to strlcpy().
strlcpy() is worse than strlcpy() because it unconditionally runs
strlen() on the source string, and the only reason we switched to
strlcpy() here was because it was lacking __must_check, which doesn't
reflect any material differences between the two function. It's just
that someone added __must_check to strscpy() and not to strlcpy().
These basic string copy operations are used in variety of ways, and
one of not-so-uncommon use cases is safely handling truncated copies,
where the caller naturally doesn't care about the return value. The
__must_check doesn't match the actual use cases and forces users to
opt for inferior variants which lack __must_check by happenstance or
spread ugly (void) casts.
Remove __must_check from strscpy() and restore strscpy() usages in
cgroup.
Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ma Shimiao <mashimiao.fnst@cn.fujitsu.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
2018-01-09 15:21:15 +00:00
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ssize_t strscpy(char *, const char *, size_t);
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2015-04-29 16:52:04 +00:00
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#endif
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2019-04-05 01:58:58 +00:00
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/* Wraps calls to strscpy()/memset(), no arch specific code required */
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ssize_t strscpy_pad(char *dest, const char *src, size_t count);
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2005-04-16 22:20:36 +00:00
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#ifndef __HAVE_ARCH_STRCAT
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extern char * strcat(char *, const char *);
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#endif
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#ifndef __HAVE_ARCH_STRNCAT
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extern char * strncat(char *, const char *, __kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_STRLCAT
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extern size_t strlcat(char *, const char *, __kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_STRCMP
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extern int strcmp(const char *,const char *);
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#endif
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#ifndef __HAVE_ARCH_STRNCMP
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extern int strncmp(const char *,const char *,__kernel_size_t);
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#endif
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2007-03-29 08:18:42 +00:00
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#ifndef __HAVE_ARCH_STRCASECMP
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extern int strcasecmp(const char *s1, const char *s2);
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#endif
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#ifndef __HAVE_ARCH_STRNCASECMP
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extern int strncasecmp(const char *s1, const char *s2, size_t n);
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#endif
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2005-04-16 22:20:36 +00:00
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#ifndef __HAVE_ARCH_STRCHR
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extern char * strchr(const char *,int);
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#endif
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2014-03-14 17:00:14 +00:00
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#ifndef __HAVE_ARCH_STRCHRNUL
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extern char * strchrnul(const char *,int);
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#endif
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2020-02-04 01:37:20 +00:00
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extern char * strnchrnul(const char *, size_t, int);
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2005-04-16 22:20:36 +00:00
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#ifndef __HAVE_ARCH_STRNCHR
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extern char * strnchr(const char *, size_t, int);
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#endif
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#ifndef __HAVE_ARCH_STRRCHR
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extern char * strrchr(const char *,int);
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#endif
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2009-12-15 02:01:04 +00:00
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extern char * __must_check skip_spaces(const char *);
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2009-12-15 02:01:15 +00:00
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extern char *strim(char *);
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static inline __must_check char *strstrip(char *str)
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{
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return strim(str);
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}
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2005-04-16 22:20:36 +00:00
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#ifndef __HAVE_ARCH_STRSTR
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2010-01-14 02:53:55 +00:00
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extern char * strstr(const char *, const char *);
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#endif
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#ifndef __HAVE_ARCH_STRNSTR
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extern char * strnstr(const char *, const char *, size_t);
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2005-04-16 22:20:36 +00:00
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#endif
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#ifndef __HAVE_ARCH_STRLEN
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extern __kernel_size_t strlen(const char *);
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#endif
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#ifndef __HAVE_ARCH_STRNLEN
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extern __kernel_size_t strnlen(const char *,__kernel_size_t);
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#endif
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2006-04-11 05:53:57 +00:00
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#ifndef __HAVE_ARCH_STRPBRK
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extern char * strpbrk(const char *,const char *);
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#endif
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#ifndef __HAVE_ARCH_STRSEP
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extern char * strsep(char **,const char *);
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#endif
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#ifndef __HAVE_ARCH_STRSPN
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extern __kernel_size_t strspn(const char *,const char *);
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#endif
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#ifndef __HAVE_ARCH_STRCSPN
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extern __kernel_size_t strcspn(const char *,const char *);
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#endif
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2005-04-16 22:20:36 +00:00
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#ifndef __HAVE_ARCH_MEMSET
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extern void * memset(void *,int,__kernel_size_t);
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#endif
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2017-09-08 23:13:48 +00:00
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#ifndef __HAVE_ARCH_MEMSET16
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extern void *memset16(uint16_t *, uint16_t, __kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_MEMSET32
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extern void *memset32(uint32_t *, uint32_t, __kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_MEMSET64
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extern void *memset64(uint64_t *, uint64_t, __kernel_size_t);
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#endif
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static inline void *memset_l(unsigned long *p, unsigned long v,
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__kernel_size_t n)
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{
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if (BITS_PER_LONG == 32)
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return memset32((uint32_t *)p, v, n);
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else
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return memset64((uint64_t *)p, v, n);
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}
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static inline void *memset_p(void **p, void *v, __kernel_size_t n)
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{
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if (BITS_PER_LONG == 32)
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return memset32((uint32_t *)p, (uintptr_t)v, n);
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else
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return memset64((uint64_t *)p, (uintptr_t)v, n);
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}
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2018-10-05 12:43:05 +00:00
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extern void **__memcat_p(void **a, void **b);
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#define memcat_p(a, b) ({ \
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BUILD_BUG_ON_MSG(!__same_type(*(a), *(b)), \
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"type mismatch in memcat_p()"); \
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(typeof(*a) *)__memcat_p((void **)(a), (void **)(b)); \
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})
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2005-04-16 22:20:36 +00:00
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#ifndef __HAVE_ARCH_MEMCPY
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extern void * memcpy(void *,const void *,__kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_MEMMOVE
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extern void * memmove(void *,const void *,__kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_MEMSCAN
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extern void * memscan(void *,int,__kernel_size_t);
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#endif
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#ifndef __HAVE_ARCH_MEMCMP
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extern int memcmp(const void *,const void *,__kernel_size_t);
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#endif
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2019-04-06 01:38:45 +00:00
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#ifndef __HAVE_ARCH_BCMP
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extern int bcmp(const void *,const void *,__kernel_size_t);
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#endif
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2005-04-16 22:20:36 +00:00
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#ifndef __HAVE_ARCH_MEMCHR
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extern void * memchr(const void *,int,__kernel_size_t);
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#endif
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2017-01-13 22:14:23 +00:00
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#ifndef __HAVE_ARCH_MEMCPY_MCSAFE
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2018-05-04 00:06:21 +00:00
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static inline __must_check unsigned long memcpy_mcsafe(void *dst,
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const void *src, size_t cnt)
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2017-01-13 22:14:23 +00:00
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{
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memcpy(dst, src, cnt);
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return 0;
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}
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#endif
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2017-05-29 19:22:50 +00:00
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#ifndef __HAVE_ARCH_MEMCPY_FLUSHCACHE
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static inline void memcpy_flushcache(void *dst, const void *src, size_t cnt)
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{
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memcpy(dst, src, cnt);
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}
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#endif
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2011-11-01 00:08:07 +00:00
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void *memchr_inv(const void *s, int c, size_t n);
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2015-06-25 22:02:22 +00:00
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char *strreplace(char *s, char old, char new);
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2005-04-16 22:20:36 +00:00
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2015-02-13 22:36:24 +00:00
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extern void kfree_const(const void *x);
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2016-05-20 00:10:55 +00:00
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extern char *kstrdup(const char *s, gfp_t gfp) __malloc;
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2015-02-13 22:36:24 +00:00
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extern const char *kstrdup_const(const char *s, gfp_t gfp);
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2007-07-18 01:37:02 +00:00
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extern char *kstrndup(const char *s, size_t len, gfp_t gfp);
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[PATCH] kmemdup: introduce
One of idiomatic ways to duplicate a region of memory is
dst = kmalloc(len, GFP_KERNEL);
if (!dst)
return -ENOMEM;
memcpy(dst, src, len);
which is neat code except a programmer needs to write size twice. Which
sometimes leads to mistakes. If len passed to kmalloc is smaller that len
passed to memcpy, it's straight overwrite-beyond-end. If len passed to
memcpy is smaller than len passed to kmalloc, it's either a) legit
behaviour ;-), or b) cloned buffer will contain garbage in second half.
Slight trolling of commit lists shows several duplications bugs
done exactly because of diverged lenghts:
Linux:
[CRYPTO]: Fix memcpy/memset args.
[PATCH] memcpy/memset fixes
OpenBSD:
kerberosV/src/lib/asn1: der_copy.c:1.4
If programmer is given only one place to play with lengths, I believe, such
mistakes could be avoided.
With kmemdup, the snippet above will be rewritten as:
dst = kmemdup(src, len, GFP_KERNEL);
if (!dst)
return -ENOMEM;
This also leads to smaller code (kzalloc effect). Quick grep shows
200+ places where kmemdup() can be used.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-10-01 06:27:20 +00:00
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extern void *kmemdup(const void *src, size_t len, gfp_t gfp);
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2017-07-04 16:25:02 +00:00
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extern char *kmemdup_nul(const char *s, size_t len, gfp_t gfp);
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2005-06-23 07:09:02 +00:00
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2007-07-18 01:37:02 +00:00
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extern char **argv_split(gfp_t gfp, const char *str, int *argcp);
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extern void argv_free(char **argv);
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2008-05-01 11:34:42 +00:00
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extern bool sysfs_streq(const char *s1, const char *s2);
|
2016-03-17 21:22:50 +00:00
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extern int kstrtobool(const char *s, bool *res);
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static inline int strtobool(const char *s, bool *res)
|
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{
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return kstrtobool(s, res);
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}
|
2008-05-01 11:34:42 +00:00
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2016-03-17 21:22:14 +00:00
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|
|
int match_string(const char * const *array, size_t n, const char *string);
|
2017-03-21 11:56:46 +00:00
|
|
|
int __sysfs_match_string(const char * const *array, size_t n, const char *s);
|
|
|
|
|
|
|
|
/**
|
|
|
|
* sysfs_match_string - matches given string in an array
|
|
|
|
* @_a: array of strings
|
|
|
|
* @_s: string to match with
|
|
|
|
*
|
|
|
|
* Helper for __sysfs_match_string(). Calculates the size of @a automatically.
|
|
|
|
*/
|
|
|
|
#define sysfs_match_string(_a, _s) __sysfs_match_string(_a, ARRAY_SIZE(_a), _s)
|
2016-03-17 21:22:14 +00:00
|
|
|
|
2009-03-06 16:21:46 +00:00
|
|
|
#ifdef CONFIG_BINARY_PRINTF
|
|
|
|
int vbin_printf(u32 *bin_buf, size_t size, const char *fmt, va_list args);
|
|
|
|
int bstr_printf(char *buf, size_t size, const char *fmt, const u32 *bin_buf);
|
|
|
|
int bprintf(u32 *bin_buf, size_t size, const char *fmt, ...) __printf(3, 4);
|
|
|
|
#endif
|
|
|
|
|
2008-07-24 04:26:44 +00:00
|
|
|
extern ssize_t memory_read_from_buffer(void *to, size_t count, loff_t *ppos,
|
2014-08-27 03:16:35 +00:00
|
|
|
const void *from, size_t available);
|
2008-07-24 04:26:44 +00:00
|
|
|
|
2019-12-01 01:50:33 +00:00
|
|
|
int ptr_to_hashval(const void *ptr, unsigned long *hashval_out);
|
|
|
|
|
2009-03-31 19:05:36 +00:00
|
|
|
/**
|
|
|
|
* strstarts - does @str start with @prefix?
|
|
|
|
* @str: string to examine
|
|
|
|
* @prefix: prefix to look for.
|
|
|
|
*/
|
|
|
|
static inline bool strstarts(const char *str, const char *prefix)
|
|
|
|
{
|
|
|
|
return strncmp(str, prefix, strlen(prefix)) == 0;
|
|
|
|
}
|
2012-07-30 21:40:55 +00:00
|
|
|
|
2014-08-27 03:16:35 +00:00
|
|
|
size_t memweight(const void *ptr, size_t bytes);
|
2019-10-07 22:00:02 +00:00
|
|
|
|
|
|
|
/**
|
|
|
|
* memzero_explicit - Fill a region of memory (e.g. sensitive
|
|
|
|
* keying data) with 0s.
|
|
|
|
* @s: Pointer to the start of the area.
|
|
|
|
* @count: The size of the area.
|
|
|
|
*
|
|
|
|
* Note: usually using memset() is just fine (!), but in cases
|
|
|
|
* where clearing out _local_ data at the end of a scope is
|
|
|
|
* necessary, memzero_explicit() should be used instead in
|
|
|
|
* order to prevent the compiler from optimising away zeroing.
|
|
|
|
*
|
|
|
|
* memzero_explicit() doesn't need an arch-specific version as
|
|
|
|
* it just invokes the one of memset() implicitly.
|
|
|
|
*/
|
|
|
|
static inline void memzero_explicit(void *s, size_t count)
|
|
|
|
{
|
|
|
|
memset(s, 0, count);
|
|
|
|
barrier_data(s);
|
|
|
|
}
|
2012-07-30 21:40:55 +00:00
|
|
|
|
2012-12-18 00:01:18 +00:00
|
|
|
/**
|
|
|
|
* kbasename - return the last part of a pathname.
|
|
|
|
*
|
|
|
|
* @path: path to extract the filename from.
|
|
|
|
*/
|
|
|
|
static inline const char *kbasename(const char *path)
|
|
|
|
{
|
|
|
|
const char *tail = strrchr(path, '/');
|
|
|
|
return tail ? tail + 1 : path;
|
|
|
|
}
|
|
|
|
|
include/linux/string.h: add the option of fortified string.h functions
This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time. Unlike glibc,
it covers buffer reads in addition to writes.
GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation. They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks. Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.
This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code. There will likely be issues caught in
regular use at runtime too.
Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:
* Some of the fortified string functions (strncpy, strcat), don't yet
place a limit on reads from the source based on __builtin_object_size of
the source buffer.
* Extending coverage to more string functions like strlcat.
* It should be possible to optionally use __builtin_object_size(x, 1) for
some functions (C strings) to detect intra-object overflows (like
glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
approach to avoid likely compatibility issues.
* The compile-time checks should be made available via a separate config
option which can be enabled by default (or always enabled) once enough
time has passed to get the issues it catches fixed.
Kees said:
"This is great to have. While it was out-of-tree code, it would have
blocked at least CVE-2016-3858 from being exploitable (improper size
argument to strlcpy()). I've sent a number of fixes for
out-of-bounds-reads that this detected upstream already"
[arnd@arndb.de: x86: fix fortified memcpy]
Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-07-12 21:36:10 +00:00
|
|
|
#define __FORTIFY_INLINE extern __always_inline __attribute__((gnu_inline))
|
|
|
|
#define __RENAME(x) __asm__(#x)
|
|
|
|
|
|
|
|
void fortify_panic(const char *name) __noreturn __cold;
|
|
|
|
void __read_overflow(void) __compiletime_error("detected read beyond size of object passed as 1st parameter");
|
|
|
|
void __read_overflow2(void) __compiletime_error("detected read beyond size of object passed as 2nd parameter");
|
2017-08-14 20:12:38 +00:00
|
|
|
void __read_overflow3(void) __compiletime_error("detected read beyond size of object passed as 3rd parameter");
|
include/linux/string.h: add the option of fortified string.h functions
This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time. Unlike glibc,
it covers buffer reads in addition to writes.
GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation. They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks. Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.
This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code. There will likely be issues caught in
regular use at runtime too.
Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:
* Some of the fortified string functions (strncpy, strcat), don't yet
place a limit on reads from the source based on __builtin_object_size of
the source buffer.
* Extending coverage to more string functions like strlcat.
* It should be possible to optionally use __builtin_object_size(x, 1) for
some functions (C strings) to detect intra-object overflows (like
glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
approach to avoid likely compatibility issues.
* The compile-time checks should be made available via a separate config
option which can be enabled by default (or always enabled) once enough
time has passed to get the issues it catches fixed.
Kees said:
"This is great to have. While it was out-of-tree code, it would have
blocked at least CVE-2016-3858 from being exploitable (improper size
argument to strlcpy()). I've sent a number of fixes for
out-of-bounds-reads that this detected upstream already"
[arnd@arndb.de: x86: fix fortified memcpy]
Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-07-12 21:36:10 +00:00
|
|
|
void __write_overflow(void) __compiletime_error("detected write beyond size of object passed as 1st parameter");
|
|
|
|
|
|
|
|
#if !defined(__NO_FORTIFY) && defined(__OPTIMIZE__) && defined(CONFIG_FORTIFY_SOURCE)
|
string.h: fix incompatibility between FORTIFY_SOURCE and KASAN
The memcmp KASAN self-test fails on a kernel with both KASAN and
FORTIFY_SOURCE.
When FORTIFY_SOURCE is on, a number of functions are replaced with
fortified versions, which attempt to check the sizes of the operands.
However, these functions often directly invoke __builtin_foo() once they
have performed the fortify check. Using __builtins may bypass KASAN
checks if the compiler decides to inline it's own implementation as
sequence of instructions, rather than emit a function call that goes out
to a KASAN-instrumented implementation.
Why is only memcmp affected?
============================
Of the string and string-like functions that kasan_test tests, only memcmp
is replaced by an inline sequence of instructions in my testing on x86
with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2).
I believe this is due to compiler heuristics. For example, if I annotate
kmalloc calls with the alloc_size annotation (and disable some fortify
compile-time checking!), the compiler will replace every memset except the
one in kmalloc_uaf_memset with inline instructions. (I have some WIP
patches to add this annotation.)
Does this affect other functions in string.h?
=============================================
Yes. Anything that uses __builtin_* rather than __real_* could be
affected. This looks like:
- strncpy
- strcat
- strlen
- strlcpy maybe, under some circumstances?
- strncat under some circumstances
- memset
- memcpy
- memmove
- memcmp (as noted)
- memchr
- strcpy
Whether a function call is emitted always depends on the compiler. Most
bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows
that this is not always the case.
Isn't FORTIFY_SOURCE disabled with KASAN?
========================================-
The string headers on all arches supporting KASAN disable fortify with
kasan, but only when address sanitisation is _also_ disabled. For example
from x86:
#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
/*
* For files that are not instrumented (e.g. mm/slub.c) we
* should use not instrumented version of mem* functions.
*/
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
#ifndef __NO_FORTIFY
#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
#endif
#endif
This comes from commit 6974f0c4555e ("include/linux/string.h: add the
option of fortified string.h functions"), and doesn't work when KASAN is
enabled and the file is supposed to be sanitised - as with test_kasan.c
I'm pretty sure this is not wrong, but not as expansive it should be:
* we shouldn't use __builtin_memcpy etc in files where we don't have
instrumentation - it could devolve into a function call to memcpy,
which will be instrumented. Rather, we should use __memcpy which
by convention is not instrumented.
* we also shouldn't be using __builtin_memcpy when we have a KASAN
instrumented file, because it could be replaced with inline asm
that will not be instrumented.
What is correct behaviour?
==========================
Firstly, there is some overlap between fortification and KASAN: both
provide some level of _runtime_ checking. Only fortify provides
compile-time checking.
KASAN and fortify can pick up different things at runtime:
- Some fortify functions, notably the string functions, could easily be
modified to consider sub-object sizes (e.g. members within a struct),
and I have some WIP patches to do this. KASAN cannot detect these
because it cannot insert poision between members of a struct.
- KASAN can detect many over-reads/over-writes when the sizes of both
operands are unknown, which fortify cannot.
So there are a couple of options:
1) Flip the test: disable fortify in santised files and enable it in
unsanitised files. This at least stops us missing KASAN checking, but
we lose the fortify checking.
2) Make the fortify code always call out to real versions. Do this only
for KASAN, for fear of losing the inlining opportunities we get from
__builtin_*.
(We can't use kasan_check_{read,write}: because the fortify functions are
_extern inline_, you can't include _static_ inline functions without a
compiler warning. kasan_check_{read,write} are static inline so we can't
use them even when they would otherwise be suitable.)
Take approach 2 and call out to real versions when KASAN is enabled.
Use __underlying_foo to distinguish from __real_foo: __real_foo always
refers to the kernel's implementation of foo, __underlying_foo could be
either the kernel implementation or the __builtin_foo implementation.
This is sometimes enough to make the memcmp test succeed with
FORTIFY_SOURCE enabled. It is at least enough to get the function call
into the module. One more fix is needed to make it reliable: see the next
patch.
Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions")
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Link: http://lkml.kernel.org/r/20200423154503.5103-3-dja@axtens.net
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-03 22:56:46 +00:00
|
|
|
|
|
|
|
#ifdef CONFIG_KASAN
|
|
|
|
extern void *__underlying_memchr(const void *p, int c, __kernel_size_t size) __RENAME(memchr);
|
|
|
|
extern int __underlying_memcmp(const void *p, const void *q, __kernel_size_t size) __RENAME(memcmp);
|
|
|
|
extern void *__underlying_memcpy(void *p, const void *q, __kernel_size_t size) __RENAME(memcpy);
|
|
|
|
extern void *__underlying_memmove(void *p, const void *q, __kernel_size_t size) __RENAME(memmove);
|
|
|
|
extern void *__underlying_memset(void *p, int c, __kernel_size_t size) __RENAME(memset);
|
|
|
|
extern char *__underlying_strcat(char *p, const char *q) __RENAME(strcat);
|
|
|
|
extern char *__underlying_strcpy(char *p, const char *q) __RENAME(strcpy);
|
|
|
|
extern __kernel_size_t __underlying_strlen(const char *p) __RENAME(strlen);
|
|
|
|
extern char *__underlying_strncat(char *p, const char *q, __kernel_size_t count) __RENAME(strncat);
|
|
|
|
extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size) __RENAME(strncpy);
|
|
|
|
#else
|
|
|
|
#define __underlying_memchr __builtin_memchr
|
|
|
|
#define __underlying_memcmp __builtin_memcmp
|
|
|
|
#define __underlying_memcpy __builtin_memcpy
|
|
|
|
#define __underlying_memmove __builtin_memmove
|
|
|
|
#define __underlying_memset __builtin_memset
|
|
|
|
#define __underlying_strcat __builtin_strcat
|
|
|
|
#define __underlying_strcpy __builtin_strcpy
|
|
|
|
#define __underlying_strlen __builtin_strlen
|
|
|
|
#define __underlying_strncat __builtin_strncat
|
|
|
|
#define __underlying_strncpy __builtin_strncpy
|
|
|
|
#endif
|
|
|
|
|
include/linux/string.h: add the option of fortified string.h functions
This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time. Unlike glibc,
it covers buffer reads in addition to writes.
GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation. They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks. Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.
This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code. There will likely be issues caught in
regular use at runtime too.
Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:
* Some of the fortified string functions (strncpy, strcat), don't yet
place a limit on reads from the source based on __builtin_object_size of
the source buffer.
* Extending coverage to more string functions like strlcat.
* It should be possible to optionally use __builtin_object_size(x, 1) for
some functions (C strings) to detect intra-object overflows (like
glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
approach to avoid likely compatibility issues.
* The compile-time checks should be made available via a separate config
option which can be enabled by default (or always enabled) once enough
time has passed to get the issues it catches fixed.
Kees said:
"This is great to have. While it was out-of-tree code, it would have
blocked at least CVE-2016-3858 from being exploitable (improper size
argument to strlcpy()). I've sent a number of fixes for
out-of-bounds-reads that this detected upstream already"
[arnd@arndb.de: x86: fix fortified memcpy]
Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-07-12 21:36:10 +00:00
|
|
|
__FORTIFY_INLINE char *strncpy(char *p, const char *q, __kernel_size_t size)
|
|
|
|
{
|
|
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
|
|
if (__builtin_constant_p(size) && p_size < size)
|
|
|
|
__write_overflow();
|
|
|
|
if (p_size < size)
|
|
|
|
fortify_panic(__func__);
|
string.h: fix incompatibility between FORTIFY_SOURCE and KASAN
The memcmp KASAN self-test fails on a kernel with both KASAN and
FORTIFY_SOURCE.
When FORTIFY_SOURCE is on, a number of functions are replaced with
fortified versions, which attempt to check the sizes of the operands.
However, these functions often directly invoke __builtin_foo() once they
have performed the fortify check. Using __builtins may bypass KASAN
checks if the compiler decides to inline it's own implementation as
sequence of instructions, rather than emit a function call that goes out
to a KASAN-instrumented implementation.
Why is only memcmp affected?
============================
Of the string and string-like functions that kasan_test tests, only memcmp
is replaced by an inline sequence of instructions in my testing on x86
with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2).
I believe this is due to compiler heuristics. For example, if I annotate
kmalloc calls with the alloc_size annotation (and disable some fortify
compile-time checking!), the compiler will replace every memset except the
one in kmalloc_uaf_memset with inline instructions. (I have some WIP
patches to add this annotation.)
Does this affect other functions in string.h?
=============================================
Yes. Anything that uses __builtin_* rather than __real_* could be
affected. This looks like:
- strncpy
- strcat
- strlen
- strlcpy maybe, under some circumstances?
- strncat under some circumstances
- memset
- memcpy
- memmove
- memcmp (as noted)
- memchr
- strcpy
Whether a function call is emitted always depends on the compiler. Most
bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows
that this is not always the case.
Isn't FORTIFY_SOURCE disabled with KASAN?
========================================-
The string headers on all arches supporting KASAN disable fortify with
kasan, but only when address sanitisation is _also_ disabled. For example
from x86:
#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
/*
* For files that are not instrumented (e.g. mm/slub.c) we
* should use not instrumented version of mem* functions.
*/
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
#ifndef __NO_FORTIFY
#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
#endif
#endif
This comes from commit 6974f0c4555e ("include/linux/string.h: add the
option of fortified string.h functions"), and doesn't work when KASAN is
enabled and the file is supposed to be sanitised - as with test_kasan.c
I'm pretty sure this is not wrong, but not as expansive it should be:
* we shouldn't use __builtin_memcpy etc in files where we don't have
instrumentation - it could devolve into a function call to memcpy,
which will be instrumented. Rather, we should use __memcpy which
by convention is not instrumented.
* we also shouldn't be using __builtin_memcpy when we have a KASAN
instrumented file, because it could be replaced with inline asm
that will not be instrumented.
What is correct behaviour?
==========================
Firstly, there is some overlap between fortification and KASAN: both
provide some level of _runtime_ checking. Only fortify provides
compile-time checking.
KASAN and fortify can pick up different things at runtime:
- Some fortify functions, notably the string functions, could easily be
modified to consider sub-object sizes (e.g. members within a struct),
and I have some WIP patches to do this. KASAN cannot detect these
because it cannot insert poision between members of a struct.
- KASAN can detect many over-reads/over-writes when the sizes of both
operands are unknown, which fortify cannot.
So there are a couple of options:
1) Flip the test: disable fortify in santised files and enable it in
unsanitised files. This at least stops us missing KASAN checking, but
we lose the fortify checking.
2) Make the fortify code always call out to real versions. Do this only
for KASAN, for fear of losing the inlining opportunities we get from
__builtin_*.
(We can't use kasan_check_{read,write}: because the fortify functions are
_extern inline_, you can't include _static_ inline functions without a
compiler warning. kasan_check_{read,write} are static inline so we can't
use them even when they would otherwise be suitable.)
Take approach 2 and call out to real versions when KASAN is enabled.
Use __underlying_foo to distinguish from __real_foo: __real_foo always
refers to the kernel's implementation of foo, __underlying_foo could be
either the kernel implementation or the __builtin_foo implementation.
This is sometimes enough to make the memcmp test succeed with
FORTIFY_SOURCE enabled. It is at least enough to get the function call
into the module. One more fix is needed to make it reliable: see the next
patch.
Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions")
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Link: http://lkml.kernel.org/r/20200423154503.5103-3-dja@axtens.net
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-03 22:56:46 +00:00
|
|
|
return __underlying_strncpy(p, q, size);
|
include/linux/string.h: add the option of fortified string.h functions
This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time. Unlike glibc,
it covers buffer reads in addition to writes.
GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation. They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks. Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.
This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code. There will likely be issues caught in
regular use at runtime too.
Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:
* Some of the fortified string functions (strncpy, strcat), don't yet
place a limit on reads from the source based on __builtin_object_size of
the source buffer.
* Extending coverage to more string functions like strlcat.
* It should be possible to optionally use __builtin_object_size(x, 1) for
some functions (C strings) to detect intra-object overflows (like
glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
approach to avoid likely compatibility issues.
* The compile-time checks should be made available via a separate config
option which can be enabled by default (or always enabled) once enough
time has passed to get the issues it catches fixed.
Kees said:
"This is great to have. While it was out-of-tree code, it would have
blocked at least CVE-2016-3858 from being exploitable (improper size
argument to strlcpy()). I've sent a number of fixes for
out-of-bounds-reads that this detected upstream already"
[arnd@arndb.de: x86: fix fortified memcpy]
Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-07-12 21:36:10 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
__FORTIFY_INLINE char *strcat(char *p, const char *q)
|
|
|
|
{
|
|
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
|
|
if (p_size == (size_t)-1)
|
string.h: fix incompatibility between FORTIFY_SOURCE and KASAN
The memcmp KASAN self-test fails on a kernel with both KASAN and
FORTIFY_SOURCE.
When FORTIFY_SOURCE is on, a number of functions are replaced with
fortified versions, which attempt to check the sizes of the operands.
However, these functions often directly invoke __builtin_foo() once they
have performed the fortify check. Using __builtins may bypass KASAN
checks if the compiler decides to inline it's own implementation as
sequence of instructions, rather than emit a function call that goes out
to a KASAN-instrumented implementation.
Why is only memcmp affected?
============================
Of the string and string-like functions that kasan_test tests, only memcmp
is replaced by an inline sequence of instructions in my testing on x86
with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2).
I believe this is due to compiler heuristics. For example, if I annotate
kmalloc calls with the alloc_size annotation (and disable some fortify
compile-time checking!), the compiler will replace every memset except the
one in kmalloc_uaf_memset with inline instructions. (I have some WIP
patches to add this annotation.)
Does this affect other functions in string.h?
=============================================
Yes. Anything that uses __builtin_* rather than __real_* could be
affected. This looks like:
- strncpy
- strcat
- strlen
- strlcpy maybe, under some circumstances?
- strncat under some circumstances
- memset
- memcpy
- memmove
- memcmp (as noted)
- memchr
- strcpy
Whether a function call is emitted always depends on the compiler. Most
bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows
that this is not always the case.
Isn't FORTIFY_SOURCE disabled with KASAN?
========================================-
The string headers on all arches supporting KASAN disable fortify with
kasan, but only when address sanitisation is _also_ disabled. For example
from x86:
#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
/*
* For files that are not instrumented (e.g. mm/slub.c) we
* should use not instrumented version of mem* functions.
*/
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
#ifndef __NO_FORTIFY
#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
#endif
#endif
This comes from commit 6974f0c4555e ("include/linux/string.h: add the
option of fortified string.h functions"), and doesn't work when KASAN is
enabled and the file is supposed to be sanitised - as with test_kasan.c
I'm pretty sure this is not wrong, but not as expansive it should be:
* we shouldn't use __builtin_memcpy etc in files where we don't have
instrumentation - it could devolve into a function call to memcpy,
which will be instrumented. Rather, we should use __memcpy which
by convention is not instrumented.
* we also shouldn't be using __builtin_memcpy when we have a KASAN
instrumented file, because it could be replaced with inline asm
that will not be instrumented.
What is correct behaviour?
==========================
Firstly, there is some overlap between fortification and KASAN: both
provide some level of _runtime_ checking. Only fortify provides
compile-time checking.
KASAN and fortify can pick up different things at runtime:
- Some fortify functions, notably the string functions, could easily be
modified to consider sub-object sizes (e.g. members within a struct),
and I have some WIP patches to do this. KASAN cannot detect these
because it cannot insert poision between members of a struct.
- KASAN can detect many over-reads/over-writes when the sizes of both
operands are unknown, which fortify cannot.
So there are a couple of options:
1) Flip the test: disable fortify in santised files and enable it in
unsanitised files. This at least stops us missing KASAN checking, but
we lose the fortify checking.
2) Make the fortify code always call out to real versions. Do this only
for KASAN, for fear of losing the inlining opportunities we get from
__builtin_*.
(We can't use kasan_check_{read,write}: because the fortify functions are
_extern inline_, you can't include _static_ inline functions without a
compiler warning. kasan_check_{read,write} are static inline so we can't
use them even when they would otherwise be suitable.)
Take approach 2 and call out to real versions when KASAN is enabled.
Use __underlying_foo to distinguish from __real_foo: __real_foo always
refers to the kernel's implementation of foo, __underlying_foo could be
either the kernel implementation or the __builtin_foo implementation.
This is sometimes enough to make the memcmp test succeed with
FORTIFY_SOURCE enabled. It is at least enough to get the function call
into the module. One more fix is needed to make it reliable: see the next
patch.
Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions")
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Link: http://lkml.kernel.org/r/20200423154503.5103-3-dja@axtens.net
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-03 22:56:46 +00:00
|
|
|
return __underlying_strcat(p, q);
|
include/linux/string.h: add the option of fortified string.h functions
This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time. Unlike glibc,
it covers buffer reads in addition to writes.
GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation. They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks. Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.
This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code. There will likely be issues caught in
regular use at runtime too.
Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:
* Some of the fortified string functions (strncpy, strcat), don't yet
place a limit on reads from the source based on __builtin_object_size of
the source buffer.
* Extending coverage to more string functions like strlcat.
* It should be possible to optionally use __builtin_object_size(x, 1) for
some functions (C strings) to detect intra-object overflows (like
glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
approach to avoid likely compatibility issues.
* The compile-time checks should be made available via a separate config
option which can be enabled by default (or always enabled) once enough
time has passed to get the issues it catches fixed.
Kees said:
"This is great to have. While it was out-of-tree code, it would have
blocked at least CVE-2016-3858 from being exploitable (improper size
argument to strlcpy()). I've sent a number of fixes for
out-of-bounds-reads that this detected upstream already"
[arnd@arndb.de: x86: fix fortified memcpy]
Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-07-12 21:36:10 +00:00
|
|
|
if (strlcat(p, q, p_size) >= p_size)
|
|
|
|
fortify_panic(__func__);
|
|
|
|
return p;
|
|
|
|
}
|
|
|
|
|
|
|
|
__FORTIFY_INLINE __kernel_size_t strlen(const char *p)
|
|
|
|
{
|
|
|
|
__kernel_size_t ret;
|
|
|
|
size_t p_size = __builtin_object_size(p, 0);
|
string.h: workaround for increased stack usage
The hardened strlen() function causes rather large stack usage in at
least one file in the kernel, in particular when CONFIG_KASAN is
enabled:
drivers/media/usb/em28xx/em28xx-dvb.c: In function 'em28xx_dvb_init':
drivers/media/usb/em28xx/em28xx-dvb.c:2062:1: error: the frame size of 3256 bytes is larger than 204 bytes [-Werror=frame-larger-than=]
Analyzing this problem led to the discovery that gcc fails to merge the
stack slots for the i2c_board_info[] structures after we strlcpy() into
them, due to the 'noreturn' attribute on the source string length check.
I reported this as a gcc bug, but it is unlikely to get fixed for gcc-8,
since it is relatively easy to work around, and it gets triggered
rarely. An earlier workaround I did added an empty inline assembly
statement before the call to fortify_panic(), which works surprisingly
well, but is really ugly and unintuitive.
This is a new approach to the same problem, this time addressing it by
not calling the 'extern __real_strnlen()' function for string constants
where __builtin_strlen() is a compile-time constant and therefore known
to be safe.
We do this by checking if the last character in the string is a
compile-time constant '\0'. If it is, we can assume that strlen() of
the string is also constant.
As a side-effect, this should also improve the object code output for
any other call of strlen() on a string constant.
[akpm@linux-foundation.org: add comment]
Link: http://lkml.kernel.org/r/20171205215143.3085755-1-arnd@arndb.de
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82365
Link: https://patchwork.kernel.org/patch/9980413/
Link: https://patchwork.kernel.org/patch/9974047/
Fixes: 6974f0c4555 ("include/linux/string.h: add the option of fortified string.h functions")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Martin Wilck <mwilck@suse.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-12-14 23:32:34 +00:00
|
|
|
|
|
|
|
/* Work around gcc excess stack consumption issue */
|
|
|
|
if (p_size == (size_t)-1 ||
|
|
|
|
(__builtin_constant_p(p[p_size - 1]) && p[p_size - 1] == '\0'))
|
string.h: fix incompatibility between FORTIFY_SOURCE and KASAN
The memcmp KASAN self-test fails on a kernel with both KASAN and
FORTIFY_SOURCE.
When FORTIFY_SOURCE is on, a number of functions are replaced with
fortified versions, which attempt to check the sizes of the operands.
However, these functions often directly invoke __builtin_foo() once they
have performed the fortify check. Using __builtins may bypass KASAN
checks if the compiler decides to inline it's own implementation as
sequence of instructions, rather than emit a function call that goes out
to a KASAN-instrumented implementation.
Why is only memcmp affected?
============================
Of the string and string-like functions that kasan_test tests, only memcmp
is replaced by an inline sequence of instructions in my testing on x86
with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2).
I believe this is due to compiler heuristics. For example, if I annotate
kmalloc calls with the alloc_size annotation (and disable some fortify
compile-time checking!), the compiler will replace every memset except the
one in kmalloc_uaf_memset with inline instructions. (I have some WIP
patches to add this annotation.)
Does this affect other functions in string.h?
=============================================
Yes. Anything that uses __builtin_* rather than __real_* could be
affected. This looks like:
- strncpy
- strcat
- strlen
- strlcpy maybe, under some circumstances?
- strncat under some circumstances
- memset
- memcpy
- memmove
- memcmp (as noted)
- memchr
- strcpy
Whether a function call is emitted always depends on the compiler. Most
bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows
that this is not always the case.
Isn't FORTIFY_SOURCE disabled with KASAN?
========================================-
The string headers on all arches supporting KASAN disable fortify with
kasan, but only when address sanitisation is _also_ disabled. For example
from x86:
#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
/*
* For files that are not instrumented (e.g. mm/slub.c) we
* should use not instrumented version of mem* functions.
*/
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
#ifndef __NO_FORTIFY
#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
#endif
#endif
This comes from commit 6974f0c4555e ("include/linux/string.h: add the
option of fortified string.h functions"), and doesn't work when KASAN is
enabled and the file is supposed to be sanitised - as with test_kasan.c
I'm pretty sure this is not wrong, but not as expansive it should be:
* we shouldn't use __builtin_memcpy etc in files where we don't have
instrumentation - it could devolve into a function call to memcpy,
which will be instrumented. Rather, we should use __memcpy which
by convention is not instrumented.
* we also shouldn't be using __builtin_memcpy when we have a KASAN
instrumented file, because it could be replaced with inline asm
that will not be instrumented.
What is correct behaviour?
==========================
Firstly, there is some overlap between fortification and KASAN: both
provide some level of _runtime_ checking. Only fortify provides
compile-time checking.
KASAN and fortify can pick up different things at runtime:
- Some fortify functions, notably the string functions, could easily be
modified to consider sub-object sizes (e.g. members within a struct),
and I have some WIP patches to do this. KASAN cannot detect these
because it cannot insert poision between members of a struct.
- KASAN can detect many over-reads/over-writes when the sizes of both
operands are unknown, which fortify cannot.
So there are a couple of options:
1) Flip the test: disable fortify in santised files and enable it in
unsanitised files. This at least stops us missing KASAN checking, but
we lose the fortify checking.
2) Make the fortify code always call out to real versions. Do this only
for KASAN, for fear of losing the inlining opportunities we get from
__builtin_*.
(We can't use kasan_check_{read,write}: because the fortify functions are
_extern inline_, you can't include _static_ inline functions without a
compiler warning. kasan_check_{read,write} are static inline so we can't
use them even when they would otherwise be suitable.)
Take approach 2 and call out to real versions when KASAN is enabled.
Use __underlying_foo to distinguish from __real_foo: __real_foo always
refers to the kernel's implementation of foo, __underlying_foo could be
either the kernel implementation or the __builtin_foo implementation.
This is sometimes enough to make the memcmp test succeed with
FORTIFY_SOURCE enabled. It is at least enough to get the function call
into the module. One more fix is needed to make it reliable: see the next
patch.
Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions")
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Link: http://lkml.kernel.org/r/20200423154503.5103-3-dja@axtens.net
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-03 22:56:46 +00:00
|
|
|
return __underlying_strlen(p);
|
include/linux/string.h: add the option of fortified string.h functions
This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time. Unlike glibc,
it covers buffer reads in addition to writes.
GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation. They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks. Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.
This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code. There will likely be issues caught in
regular use at runtime too.
Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:
* Some of the fortified string functions (strncpy, strcat), don't yet
place a limit on reads from the source based on __builtin_object_size of
the source buffer.
* Extending coverage to more string functions like strlcat.
* It should be possible to optionally use __builtin_object_size(x, 1) for
some functions (C strings) to detect intra-object overflows (like
glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
approach to avoid likely compatibility issues.
* The compile-time checks should be made available via a separate config
option which can be enabled by default (or always enabled) once enough
time has passed to get the issues it catches fixed.
Kees said:
"This is great to have. While it was out-of-tree code, it would have
blocked at least CVE-2016-3858 from being exploitable (improper size
argument to strlcpy()). I've sent a number of fixes for
out-of-bounds-reads that this detected upstream already"
[arnd@arndb.de: x86: fix fortified memcpy]
Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-07-12 21:36:10 +00:00
|
|
|
ret = strnlen(p, p_size);
|
|
|
|
if (p_size <= ret)
|
|
|
|
fortify_panic(__func__);
|
|
|
|
return ret;
|
|
|
|
}
|
|
|
|
|
|
|
|
extern __kernel_size_t __real_strnlen(const char *, __kernel_size_t) __RENAME(strnlen);
|
|
|
|
__FORTIFY_INLINE __kernel_size_t strnlen(const char *p, __kernel_size_t maxlen)
|
|
|
|
{
|
|
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
|
|
__kernel_size_t ret = __real_strnlen(p, maxlen < p_size ? maxlen : p_size);
|
|
|
|
if (p_size <= ret && maxlen != ret)
|
|
|
|
fortify_panic(__func__);
|
|
|
|
return ret;
|
|
|
|
}
|
|
|
|
|
|
|
|
/* defined after fortified strlen to reuse it */
|
|
|
|
extern size_t __real_strlcpy(char *, const char *, size_t) __RENAME(strlcpy);
|
|
|
|
__FORTIFY_INLINE size_t strlcpy(char *p, const char *q, size_t size)
|
|
|
|
{
|
|
|
|
size_t ret;
|
|
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
|
|
size_t q_size = __builtin_object_size(q, 0);
|
|
|
|
if (p_size == (size_t)-1 && q_size == (size_t)-1)
|
|
|
|
return __real_strlcpy(p, q, size);
|
|
|
|
ret = strlen(q);
|
|
|
|
if (size) {
|
|
|
|
size_t len = (ret >= size) ? size - 1 : ret;
|
|
|
|
if (__builtin_constant_p(len) && len >= p_size)
|
|
|
|
__write_overflow();
|
|
|
|
if (len >= p_size)
|
|
|
|
fortify_panic(__func__);
|
string.h: fix incompatibility between FORTIFY_SOURCE and KASAN
The memcmp KASAN self-test fails on a kernel with both KASAN and
FORTIFY_SOURCE.
When FORTIFY_SOURCE is on, a number of functions are replaced with
fortified versions, which attempt to check the sizes of the operands.
However, these functions often directly invoke __builtin_foo() once they
have performed the fortify check. Using __builtins may bypass KASAN
checks if the compiler decides to inline it's own implementation as
sequence of instructions, rather than emit a function call that goes out
to a KASAN-instrumented implementation.
Why is only memcmp affected?
============================
Of the string and string-like functions that kasan_test tests, only memcmp
is replaced by an inline sequence of instructions in my testing on x86
with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2).
I believe this is due to compiler heuristics. For example, if I annotate
kmalloc calls with the alloc_size annotation (and disable some fortify
compile-time checking!), the compiler will replace every memset except the
one in kmalloc_uaf_memset with inline instructions. (I have some WIP
patches to add this annotation.)
Does this affect other functions in string.h?
=============================================
Yes. Anything that uses __builtin_* rather than __real_* could be
affected. This looks like:
- strncpy
- strcat
- strlen
- strlcpy maybe, under some circumstances?
- strncat under some circumstances
- memset
- memcpy
- memmove
- memcmp (as noted)
- memchr
- strcpy
Whether a function call is emitted always depends on the compiler. Most
bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows
that this is not always the case.
Isn't FORTIFY_SOURCE disabled with KASAN?
========================================-
The string headers on all arches supporting KASAN disable fortify with
kasan, but only when address sanitisation is _also_ disabled. For example
from x86:
#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
/*
* For files that are not instrumented (e.g. mm/slub.c) we
* should use not instrumented version of mem* functions.
*/
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
#ifndef __NO_FORTIFY
#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
#endif
#endif
This comes from commit 6974f0c4555e ("include/linux/string.h: add the
option of fortified string.h functions"), and doesn't work when KASAN is
enabled and the file is supposed to be sanitised - as with test_kasan.c
I'm pretty sure this is not wrong, but not as expansive it should be:
* we shouldn't use __builtin_memcpy etc in files where we don't have
instrumentation - it could devolve into a function call to memcpy,
which will be instrumented. Rather, we should use __memcpy which
by convention is not instrumented.
* we also shouldn't be using __builtin_memcpy when we have a KASAN
instrumented file, because it could be replaced with inline asm
that will not be instrumented.
What is correct behaviour?
==========================
Firstly, there is some overlap between fortification and KASAN: both
provide some level of _runtime_ checking. Only fortify provides
compile-time checking.
KASAN and fortify can pick up different things at runtime:
- Some fortify functions, notably the string functions, could easily be
modified to consider sub-object sizes (e.g. members within a struct),
and I have some WIP patches to do this. KASAN cannot detect these
because it cannot insert poision between members of a struct.
- KASAN can detect many over-reads/over-writes when the sizes of both
operands are unknown, which fortify cannot.
So there are a couple of options:
1) Flip the test: disable fortify in santised files and enable it in
unsanitised files. This at least stops us missing KASAN checking, but
we lose the fortify checking.
2) Make the fortify code always call out to real versions. Do this only
for KASAN, for fear of losing the inlining opportunities we get from
__builtin_*.
(We can't use kasan_check_{read,write}: because the fortify functions are
_extern inline_, you can't include _static_ inline functions without a
compiler warning. kasan_check_{read,write} are static inline so we can't
use them even when they would otherwise be suitable.)
Take approach 2 and call out to real versions when KASAN is enabled.
Use __underlying_foo to distinguish from __real_foo: __real_foo always
refers to the kernel's implementation of foo, __underlying_foo could be
either the kernel implementation or the __builtin_foo implementation.
This is sometimes enough to make the memcmp test succeed with
FORTIFY_SOURCE enabled. It is at least enough to get the function call
into the module. One more fix is needed to make it reliable: see the next
patch.
Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions")
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Link: http://lkml.kernel.org/r/20200423154503.5103-3-dja@axtens.net
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-03 22:56:46 +00:00
|
|
|
__underlying_memcpy(p, q, len);
|
include/linux/string.h: add the option of fortified string.h functions
This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time. Unlike glibc,
it covers buffer reads in addition to writes.
GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation. They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks. Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.
This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code. There will likely be issues caught in
regular use at runtime too.
Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:
* Some of the fortified string functions (strncpy, strcat), don't yet
place a limit on reads from the source based on __builtin_object_size of
the source buffer.
* Extending coverage to more string functions like strlcat.
* It should be possible to optionally use __builtin_object_size(x, 1) for
some functions (C strings) to detect intra-object overflows (like
glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
approach to avoid likely compatibility issues.
* The compile-time checks should be made available via a separate config
option which can be enabled by default (or always enabled) once enough
time has passed to get the issues it catches fixed.
Kees said:
"This is great to have. While it was out-of-tree code, it would have
blocked at least CVE-2016-3858 from being exploitable (improper size
argument to strlcpy()). I've sent a number of fixes for
out-of-bounds-reads that this detected upstream already"
[arnd@arndb.de: x86: fix fortified memcpy]
Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-07-12 21:36:10 +00:00
|
|
|
p[len] = '\0';
|
|
|
|
}
|
|
|
|
return ret;
|
|
|
|
}
|
|
|
|
|
|
|
|
/* defined after fortified strlen and strnlen to reuse them */
|
|
|
|
__FORTIFY_INLINE char *strncat(char *p, const char *q, __kernel_size_t count)
|
|
|
|
{
|
|
|
|
size_t p_len, copy_len;
|
|
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
|
|
size_t q_size = __builtin_object_size(q, 0);
|
|
|
|
if (p_size == (size_t)-1 && q_size == (size_t)-1)
|
string.h: fix incompatibility between FORTIFY_SOURCE and KASAN
The memcmp KASAN self-test fails on a kernel with both KASAN and
FORTIFY_SOURCE.
When FORTIFY_SOURCE is on, a number of functions are replaced with
fortified versions, which attempt to check the sizes of the operands.
However, these functions often directly invoke __builtin_foo() once they
have performed the fortify check. Using __builtins may bypass KASAN
checks if the compiler decides to inline it's own implementation as
sequence of instructions, rather than emit a function call that goes out
to a KASAN-instrumented implementation.
Why is only memcmp affected?
============================
Of the string and string-like functions that kasan_test tests, only memcmp
is replaced by an inline sequence of instructions in my testing on x86
with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2).
I believe this is due to compiler heuristics. For example, if I annotate
kmalloc calls with the alloc_size annotation (and disable some fortify
compile-time checking!), the compiler will replace every memset except the
one in kmalloc_uaf_memset with inline instructions. (I have some WIP
patches to add this annotation.)
Does this affect other functions in string.h?
=============================================
Yes. Anything that uses __builtin_* rather than __real_* could be
affected. This looks like:
- strncpy
- strcat
- strlen
- strlcpy maybe, under some circumstances?
- strncat under some circumstances
- memset
- memcpy
- memmove
- memcmp (as noted)
- memchr
- strcpy
Whether a function call is emitted always depends on the compiler. Most
bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows
that this is not always the case.
Isn't FORTIFY_SOURCE disabled with KASAN?
========================================-
The string headers on all arches supporting KASAN disable fortify with
kasan, but only when address sanitisation is _also_ disabled. For example
from x86:
#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
/*
* For files that are not instrumented (e.g. mm/slub.c) we
* should use not instrumented version of mem* functions.
*/
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
#ifndef __NO_FORTIFY
#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
#endif
#endif
This comes from commit 6974f0c4555e ("include/linux/string.h: add the
option of fortified string.h functions"), and doesn't work when KASAN is
enabled and the file is supposed to be sanitised - as with test_kasan.c
I'm pretty sure this is not wrong, but not as expansive it should be:
* we shouldn't use __builtin_memcpy etc in files where we don't have
instrumentation - it could devolve into a function call to memcpy,
which will be instrumented. Rather, we should use __memcpy which
by convention is not instrumented.
* we also shouldn't be using __builtin_memcpy when we have a KASAN
instrumented file, because it could be replaced with inline asm
that will not be instrumented.
What is correct behaviour?
==========================
Firstly, there is some overlap between fortification and KASAN: both
provide some level of _runtime_ checking. Only fortify provides
compile-time checking.
KASAN and fortify can pick up different things at runtime:
- Some fortify functions, notably the string functions, could easily be
modified to consider sub-object sizes (e.g. members within a struct),
and I have some WIP patches to do this. KASAN cannot detect these
because it cannot insert poision between members of a struct.
- KASAN can detect many over-reads/over-writes when the sizes of both
operands are unknown, which fortify cannot.
So there are a couple of options:
1) Flip the test: disable fortify in santised files and enable it in
unsanitised files. This at least stops us missing KASAN checking, but
we lose the fortify checking.
2) Make the fortify code always call out to real versions. Do this only
for KASAN, for fear of losing the inlining opportunities we get from
__builtin_*.
(We can't use kasan_check_{read,write}: because the fortify functions are
_extern inline_, you can't include _static_ inline functions without a
compiler warning. kasan_check_{read,write} are static inline so we can't
use them even when they would otherwise be suitable.)
Take approach 2 and call out to real versions when KASAN is enabled.
Use __underlying_foo to distinguish from __real_foo: __real_foo always
refers to the kernel's implementation of foo, __underlying_foo could be
either the kernel implementation or the __builtin_foo implementation.
This is sometimes enough to make the memcmp test succeed with
FORTIFY_SOURCE enabled. It is at least enough to get the function call
into the module. One more fix is needed to make it reliable: see the next
patch.
Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions")
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Link: http://lkml.kernel.org/r/20200423154503.5103-3-dja@axtens.net
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-03 22:56:46 +00:00
|
|
|
return __underlying_strncat(p, q, count);
|
include/linux/string.h: add the option of fortified string.h functions
This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time. Unlike glibc,
it covers buffer reads in addition to writes.
GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation. They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks. Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.
This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code. There will likely be issues caught in
regular use at runtime too.
Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:
* Some of the fortified string functions (strncpy, strcat), don't yet
place a limit on reads from the source based on __builtin_object_size of
the source buffer.
* Extending coverage to more string functions like strlcat.
* It should be possible to optionally use __builtin_object_size(x, 1) for
some functions (C strings) to detect intra-object overflows (like
glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
approach to avoid likely compatibility issues.
* The compile-time checks should be made available via a separate config
option which can be enabled by default (or always enabled) once enough
time has passed to get the issues it catches fixed.
Kees said:
"This is great to have. While it was out-of-tree code, it would have
blocked at least CVE-2016-3858 from being exploitable (improper size
argument to strlcpy()). I've sent a number of fixes for
out-of-bounds-reads that this detected upstream already"
[arnd@arndb.de: x86: fix fortified memcpy]
Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-07-12 21:36:10 +00:00
|
|
|
p_len = strlen(p);
|
|
|
|
copy_len = strnlen(q, count);
|
|
|
|
if (p_size < p_len + copy_len + 1)
|
|
|
|
fortify_panic(__func__);
|
string.h: fix incompatibility between FORTIFY_SOURCE and KASAN
The memcmp KASAN self-test fails on a kernel with both KASAN and
FORTIFY_SOURCE.
When FORTIFY_SOURCE is on, a number of functions are replaced with
fortified versions, which attempt to check the sizes of the operands.
However, these functions often directly invoke __builtin_foo() once they
have performed the fortify check. Using __builtins may bypass KASAN
checks if the compiler decides to inline it's own implementation as
sequence of instructions, rather than emit a function call that goes out
to a KASAN-instrumented implementation.
Why is only memcmp affected?
============================
Of the string and string-like functions that kasan_test tests, only memcmp
is replaced by an inline sequence of instructions in my testing on x86
with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2).
I believe this is due to compiler heuristics. For example, if I annotate
kmalloc calls with the alloc_size annotation (and disable some fortify
compile-time checking!), the compiler will replace every memset except the
one in kmalloc_uaf_memset with inline instructions. (I have some WIP
patches to add this annotation.)
Does this affect other functions in string.h?
=============================================
Yes. Anything that uses __builtin_* rather than __real_* could be
affected. This looks like:
- strncpy
- strcat
- strlen
- strlcpy maybe, under some circumstances?
- strncat under some circumstances
- memset
- memcpy
- memmove
- memcmp (as noted)
- memchr
- strcpy
Whether a function call is emitted always depends on the compiler. Most
bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows
that this is not always the case.
Isn't FORTIFY_SOURCE disabled with KASAN?
========================================-
The string headers on all arches supporting KASAN disable fortify with
kasan, but only when address sanitisation is _also_ disabled. For example
from x86:
#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
/*
* For files that are not instrumented (e.g. mm/slub.c) we
* should use not instrumented version of mem* functions.
*/
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
#ifndef __NO_FORTIFY
#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
#endif
#endif
This comes from commit 6974f0c4555e ("include/linux/string.h: add the
option of fortified string.h functions"), and doesn't work when KASAN is
enabled and the file is supposed to be sanitised - as with test_kasan.c
I'm pretty sure this is not wrong, but not as expansive it should be:
* we shouldn't use __builtin_memcpy etc in files where we don't have
instrumentation - it could devolve into a function call to memcpy,
which will be instrumented. Rather, we should use __memcpy which
by convention is not instrumented.
* we also shouldn't be using __builtin_memcpy when we have a KASAN
instrumented file, because it could be replaced with inline asm
that will not be instrumented.
What is correct behaviour?
==========================
Firstly, there is some overlap between fortification and KASAN: both
provide some level of _runtime_ checking. Only fortify provides
compile-time checking.
KASAN and fortify can pick up different things at runtime:
- Some fortify functions, notably the string functions, could easily be
modified to consider sub-object sizes (e.g. members within a struct),
and I have some WIP patches to do this. KASAN cannot detect these
because it cannot insert poision between members of a struct.
- KASAN can detect many over-reads/over-writes when the sizes of both
operands are unknown, which fortify cannot.
So there are a couple of options:
1) Flip the test: disable fortify in santised files and enable it in
unsanitised files. This at least stops us missing KASAN checking, but
we lose the fortify checking.
2) Make the fortify code always call out to real versions. Do this only
for KASAN, for fear of losing the inlining opportunities we get from
__builtin_*.
(We can't use kasan_check_{read,write}: because the fortify functions are
_extern inline_, you can't include _static_ inline functions without a
compiler warning. kasan_check_{read,write} are static inline so we can't
use them even when they would otherwise be suitable.)
Take approach 2 and call out to real versions when KASAN is enabled.
Use __underlying_foo to distinguish from __real_foo: __real_foo always
refers to the kernel's implementation of foo, __underlying_foo could be
either the kernel implementation or the __builtin_foo implementation.
This is sometimes enough to make the memcmp test succeed with
FORTIFY_SOURCE enabled. It is at least enough to get the function call
into the module. One more fix is needed to make it reliable: see the next
patch.
Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions")
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Link: http://lkml.kernel.org/r/20200423154503.5103-3-dja@axtens.net
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-03 22:56:46 +00:00
|
|
|
__underlying_memcpy(p + p_len, q, copy_len);
|
include/linux/string.h: add the option of fortified string.h functions
This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time. Unlike glibc,
it covers buffer reads in addition to writes.
GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation. They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks. Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.
This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code. There will likely be issues caught in
regular use at runtime too.
Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:
* Some of the fortified string functions (strncpy, strcat), don't yet
place a limit on reads from the source based on __builtin_object_size of
the source buffer.
* Extending coverage to more string functions like strlcat.
* It should be possible to optionally use __builtin_object_size(x, 1) for
some functions (C strings) to detect intra-object overflows (like
glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
approach to avoid likely compatibility issues.
* The compile-time checks should be made available via a separate config
option which can be enabled by default (or always enabled) once enough
time has passed to get the issues it catches fixed.
Kees said:
"This is great to have. While it was out-of-tree code, it would have
blocked at least CVE-2016-3858 from being exploitable (improper size
argument to strlcpy()). I've sent a number of fixes for
out-of-bounds-reads that this detected upstream already"
[arnd@arndb.de: x86: fix fortified memcpy]
Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-07-12 21:36:10 +00:00
|
|
|
p[p_len + copy_len] = '\0';
|
|
|
|
return p;
|
|
|
|
}
|
|
|
|
|
|
|
|
__FORTIFY_INLINE void *memset(void *p, int c, __kernel_size_t size)
|
|
|
|
{
|
|
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
|
|
if (__builtin_constant_p(size) && p_size < size)
|
|
|
|
__write_overflow();
|
|
|
|
if (p_size < size)
|
|
|
|
fortify_panic(__func__);
|
string.h: fix incompatibility between FORTIFY_SOURCE and KASAN
The memcmp KASAN self-test fails on a kernel with both KASAN and
FORTIFY_SOURCE.
When FORTIFY_SOURCE is on, a number of functions are replaced with
fortified versions, which attempt to check the sizes of the operands.
However, these functions often directly invoke __builtin_foo() once they
have performed the fortify check. Using __builtins may bypass KASAN
checks if the compiler decides to inline it's own implementation as
sequence of instructions, rather than emit a function call that goes out
to a KASAN-instrumented implementation.
Why is only memcmp affected?
============================
Of the string and string-like functions that kasan_test tests, only memcmp
is replaced by an inline sequence of instructions in my testing on x86
with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2).
I believe this is due to compiler heuristics. For example, if I annotate
kmalloc calls with the alloc_size annotation (and disable some fortify
compile-time checking!), the compiler will replace every memset except the
one in kmalloc_uaf_memset with inline instructions. (I have some WIP
patches to add this annotation.)
Does this affect other functions in string.h?
=============================================
Yes. Anything that uses __builtin_* rather than __real_* could be
affected. This looks like:
- strncpy
- strcat
- strlen
- strlcpy maybe, under some circumstances?
- strncat under some circumstances
- memset
- memcpy
- memmove
- memcmp (as noted)
- memchr
- strcpy
Whether a function call is emitted always depends on the compiler. Most
bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows
that this is not always the case.
Isn't FORTIFY_SOURCE disabled with KASAN?
========================================-
The string headers on all arches supporting KASAN disable fortify with
kasan, but only when address sanitisation is _also_ disabled. For example
from x86:
#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
/*
* For files that are not instrumented (e.g. mm/slub.c) we
* should use not instrumented version of mem* functions.
*/
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
#ifndef __NO_FORTIFY
#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
#endif
#endif
This comes from commit 6974f0c4555e ("include/linux/string.h: add the
option of fortified string.h functions"), and doesn't work when KASAN is
enabled and the file is supposed to be sanitised - as with test_kasan.c
I'm pretty sure this is not wrong, but not as expansive it should be:
* we shouldn't use __builtin_memcpy etc in files where we don't have
instrumentation - it could devolve into a function call to memcpy,
which will be instrumented. Rather, we should use __memcpy which
by convention is not instrumented.
* we also shouldn't be using __builtin_memcpy when we have a KASAN
instrumented file, because it could be replaced with inline asm
that will not be instrumented.
What is correct behaviour?
==========================
Firstly, there is some overlap between fortification and KASAN: both
provide some level of _runtime_ checking. Only fortify provides
compile-time checking.
KASAN and fortify can pick up different things at runtime:
- Some fortify functions, notably the string functions, could easily be
modified to consider sub-object sizes (e.g. members within a struct),
and I have some WIP patches to do this. KASAN cannot detect these
because it cannot insert poision between members of a struct.
- KASAN can detect many over-reads/over-writes when the sizes of both
operands are unknown, which fortify cannot.
So there are a couple of options:
1) Flip the test: disable fortify in santised files and enable it in
unsanitised files. This at least stops us missing KASAN checking, but
we lose the fortify checking.
2) Make the fortify code always call out to real versions. Do this only
for KASAN, for fear of losing the inlining opportunities we get from
__builtin_*.
(We can't use kasan_check_{read,write}: because the fortify functions are
_extern inline_, you can't include _static_ inline functions without a
compiler warning. kasan_check_{read,write} are static inline so we can't
use them even when they would otherwise be suitable.)
Take approach 2 and call out to real versions when KASAN is enabled.
Use __underlying_foo to distinguish from __real_foo: __real_foo always
refers to the kernel's implementation of foo, __underlying_foo could be
either the kernel implementation or the __builtin_foo implementation.
This is sometimes enough to make the memcmp test succeed with
FORTIFY_SOURCE enabled. It is at least enough to get the function call
into the module. One more fix is needed to make it reliable: see the next
patch.
Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions")
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Link: http://lkml.kernel.org/r/20200423154503.5103-3-dja@axtens.net
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-03 22:56:46 +00:00
|
|
|
return __underlying_memset(p, c, size);
|
include/linux/string.h: add the option of fortified string.h functions
This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time. Unlike glibc,
it covers buffer reads in addition to writes.
GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation. They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks. Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.
This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code. There will likely be issues caught in
regular use at runtime too.
Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:
* Some of the fortified string functions (strncpy, strcat), don't yet
place a limit on reads from the source based on __builtin_object_size of
the source buffer.
* Extending coverage to more string functions like strlcat.
* It should be possible to optionally use __builtin_object_size(x, 1) for
some functions (C strings) to detect intra-object overflows (like
glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
approach to avoid likely compatibility issues.
* The compile-time checks should be made available via a separate config
option which can be enabled by default (or always enabled) once enough
time has passed to get the issues it catches fixed.
Kees said:
"This is great to have. While it was out-of-tree code, it would have
blocked at least CVE-2016-3858 from being exploitable (improper size
argument to strlcpy()). I've sent a number of fixes for
out-of-bounds-reads that this detected upstream already"
[arnd@arndb.de: x86: fix fortified memcpy]
Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-07-12 21:36:10 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
__FORTIFY_INLINE void *memcpy(void *p, const void *q, __kernel_size_t size)
|
|
|
|
{
|
|
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
|
|
size_t q_size = __builtin_object_size(q, 0);
|
|
|
|
if (__builtin_constant_p(size)) {
|
|
|
|
if (p_size < size)
|
|
|
|
__write_overflow();
|
|
|
|
if (q_size < size)
|
|
|
|
__read_overflow2();
|
|
|
|
}
|
|
|
|
if (p_size < size || q_size < size)
|
|
|
|
fortify_panic(__func__);
|
string.h: fix incompatibility between FORTIFY_SOURCE and KASAN
The memcmp KASAN self-test fails on a kernel with both KASAN and
FORTIFY_SOURCE.
When FORTIFY_SOURCE is on, a number of functions are replaced with
fortified versions, which attempt to check the sizes of the operands.
However, these functions often directly invoke __builtin_foo() once they
have performed the fortify check. Using __builtins may bypass KASAN
checks if the compiler decides to inline it's own implementation as
sequence of instructions, rather than emit a function call that goes out
to a KASAN-instrumented implementation.
Why is only memcmp affected?
============================
Of the string and string-like functions that kasan_test tests, only memcmp
is replaced by an inline sequence of instructions in my testing on x86
with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2).
I believe this is due to compiler heuristics. For example, if I annotate
kmalloc calls with the alloc_size annotation (and disable some fortify
compile-time checking!), the compiler will replace every memset except the
one in kmalloc_uaf_memset with inline instructions. (I have some WIP
patches to add this annotation.)
Does this affect other functions in string.h?
=============================================
Yes. Anything that uses __builtin_* rather than __real_* could be
affected. This looks like:
- strncpy
- strcat
- strlen
- strlcpy maybe, under some circumstances?
- strncat under some circumstances
- memset
- memcpy
- memmove
- memcmp (as noted)
- memchr
- strcpy
Whether a function call is emitted always depends on the compiler. Most
bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows
that this is not always the case.
Isn't FORTIFY_SOURCE disabled with KASAN?
========================================-
The string headers on all arches supporting KASAN disable fortify with
kasan, but only when address sanitisation is _also_ disabled. For example
from x86:
#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
/*
* For files that are not instrumented (e.g. mm/slub.c) we
* should use not instrumented version of mem* functions.
*/
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
#ifndef __NO_FORTIFY
#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
#endif
#endif
This comes from commit 6974f0c4555e ("include/linux/string.h: add the
option of fortified string.h functions"), and doesn't work when KASAN is
enabled and the file is supposed to be sanitised - as with test_kasan.c
I'm pretty sure this is not wrong, but not as expansive it should be:
* we shouldn't use __builtin_memcpy etc in files where we don't have
instrumentation - it could devolve into a function call to memcpy,
which will be instrumented. Rather, we should use __memcpy which
by convention is not instrumented.
* we also shouldn't be using __builtin_memcpy when we have a KASAN
instrumented file, because it could be replaced with inline asm
that will not be instrumented.
What is correct behaviour?
==========================
Firstly, there is some overlap between fortification and KASAN: both
provide some level of _runtime_ checking. Only fortify provides
compile-time checking.
KASAN and fortify can pick up different things at runtime:
- Some fortify functions, notably the string functions, could easily be
modified to consider sub-object sizes (e.g. members within a struct),
and I have some WIP patches to do this. KASAN cannot detect these
because it cannot insert poision between members of a struct.
- KASAN can detect many over-reads/over-writes when the sizes of both
operands are unknown, which fortify cannot.
So there are a couple of options:
1) Flip the test: disable fortify in santised files and enable it in
unsanitised files. This at least stops us missing KASAN checking, but
we lose the fortify checking.
2) Make the fortify code always call out to real versions. Do this only
for KASAN, for fear of losing the inlining opportunities we get from
__builtin_*.
(We can't use kasan_check_{read,write}: because the fortify functions are
_extern inline_, you can't include _static_ inline functions without a
compiler warning. kasan_check_{read,write} are static inline so we can't
use them even when they would otherwise be suitable.)
Take approach 2 and call out to real versions when KASAN is enabled.
Use __underlying_foo to distinguish from __real_foo: __real_foo always
refers to the kernel's implementation of foo, __underlying_foo could be
either the kernel implementation or the __builtin_foo implementation.
This is sometimes enough to make the memcmp test succeed with
FORTIFY_SOURCE enabled. It is at least enough to get the function call
into the module. One more fix is needed to make it reliable: see the next
patch.
Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions")
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Link: http://lkml.kernel.org/r/20200423154503.5103-3-dja@axtens.net
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-03 22:56:46 +00:00
|
|
|
return __underlying_memcpy(p, q, size);
|
include/linux/string.h: add the option of fortified string.h functions
This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time. Unlike glibc,
it covers buffer reads in addition to writes.
GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation. They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks. Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.
This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code. There will likely be issues caught in
regular use at runtime too.
Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:
* Some of the fortified string functions (strncpy, strcat), don't yet
place a limit on reads from the source based on __builtin_object_size of
the source buffer.
* Extending coverage to more string functions like strlcat.
* It should be possible to optionally use __builtin_object_size(x, 1) for
some functions (C strings) to detect intra-object overflows (like
glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
approach to avoid likely compatibility issues.
* The compile-time checks should be made available via a separate config
option which can be enabled by default (or always enabled) once enough
time has passed to get the issues it catches fixed.
Kees said:
"This is great to have. While it was out-of-tree code, it would have
blocked at least CVE-2016-3858 from being exploitable (improper size
argument to strlcpy()). I've sent a number of fixes for
out-of-bounds-reads that this detected upstream already"
[arnd@arndb.de: x86: fix fortified memcpy]
Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-07-12 21:36:10 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
__FORTIFY_INLINE void *memmove(void *p, const void *q, __kernel_size_t size)
|
|
|
|
{
|
|
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
|
|
size_t q_size = __builtin_object_size(q, 0);
|
|
|
|
if (__builtin_constant_p(size)) {
|
|
|
|
if (p_size < size)
|
|
|
|
__write_overflow();
|
|
|
|
if (q_size < size)
|
|
|
|
__read_overflow2();
|
|
|
|
}
|
|
|
|
if (p_size < size || q_size < size)
|
|
|
|
fortify_panic(__func__);
|
string.h: fix incompatibility between FORTIFY_SOURCE and KASAN
The memcmp KASAN self-test fails on a kernel with both KASAN and
FORTIFY_SOURCE.
When FORTIFY_SOURCE is on, a number of functions are replaced with
fortified versions, which attempt to check the sizes of the operands.
However, these functions often directly invoke __builtin_foo() once they
have performed the fortify check. Using __builtins may bypass KASAN
checks if the compiler decides to inline it's own implementation as
sequence of instructions, rather than emit a function call that goes out
to a KASAN-instrumented implementation.
Why is only memcmp affected?
============================
Of the string and string-like functions that kasan_test tests, only memcmp
is replaced by an inline sequence of instructions in my testing on x86
with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2).
I believe this is due to compiler heuristics. For example, if I annotate
kmalloc calls with the alloc_size annotation (and disable some fortify
compile-time checking!), the compiler will replace every memset except the
one in kmalloc_uaf_memset with inline instructions. (I have some WIP
patches to add this annotation.)
Does this affect other functions in string.h?
=============================================
Yes. Anything that uses __builtin_* rather than __real_* could be
affected. This looks like:
- strncpy
- strcat
- strlen
- strlcpy maybe, under some circumstances?
- strncat under some circumstances
- memset
- memcpy
- memmove
- memcmp (as noted)
- memchr
- strcpy
Whether a function call is emitted always depends on the compiler. Most
bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows
that this is not always the case.
Isn't FORTIFY_SOURCE disabled with KASAN?
========================================-
The string headers on all arches supporting KASAN disable fortify with
kasan, but only when address sanitisation is _also_ disabled. For example
from x86:
#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
/*
* For files that are not instrumented (e.g. mm/slub.c) we
* should use not instrumented version of mem* functions.
*/
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
#ifndef __NO_FORTIFY
#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
#endif
#endif
This comes from commit 6974f0c4555e ("include/linux/string.h: add the
option of fortified string.h functions"), and doesn't work when KASAN is
enabled and the file is supposed to be sanitised - as with test_kasan.c
I'm pretty sure this is not wrong, but not as expansive it should be:
* we shouldn't use __builtin_memcpy etc in files where we don't have
instrumentation - it could devolve into a function call to memcpy,
which will be instrumented. Rather, we should use __memcpy which
by convention is not instrumented.
* we also shouldn't be using __builtin_memcpy when we have a KASAN
instrumented file, because it could be replaced with inline asm
that will not be instrumented.
What is correct behaviour?
==========================
Firstly, there is some overlap between fortification and KASAN: both
provide some level of _runtime_ checking. Only fortify provides
compile-time checking.
KASAN and fortify can pick up different things at runtime:
- Some fortify functions, notably the string functions, could easily be
modified to consider sub-object sizes (e.g. members within a struct),
and I have some WIP patches to do this. KASAN cannot detect these
because it cannot insert poision between members of a struct.
- KASAN can detect many over-reads/over-writes when the sizes of both
operands are unknown, which fortify cannot.
So there are a couple of options:
1) Flip the test: disable fortify in santised files and enable it in
unsanitised files. This at least stops us missing KASAN checking, but
we lose the fortify checking.
2) Make the fortify code always call out to real versions. Do this only
for KASAN, for fear of losing the inlining opportunities we get from
__builtin_*.
(We can't use kasan_check_{read,write}: because the fortify functions are
_extern inline_, you can't include _static_ inline functions without a
compiler warning. kasan_check_{read,write} are static inline so we can't
use them even when they would otherwise be suitable.)
Take approach 2 and call out to real versions when KASAN is enabled.
Use __underlying_foo to distinguish from __real_foo: __real_foo always
refers to the kernel's implementation of foo, __underlying_foo could be
either the kernel implementation or the __builtin_foo implementation.
This is sometimes enough to make the memcmp test succeed with
FORTIFY_SOURCE enabled. It is at least enough to get the function call
into the module. One more fix is needed to make it reliable: see the next
patch.
Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions")
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Link: http://lkml.kernel.org/r/20200423154503.5103-3-dja@axtens.net
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-03 22:56:46 +00:00
|
|
|
return __underlying_memmove(p, q, size);
|
include/linux/string.h: add the option of fortified string.h functions
This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time. Unlike glibc,
it covers buffer reads in addition to writes.
GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation. They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks. Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.
This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code. There will likely be issues caught in
regular use at runtime too.
Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:
* Some of the fortified string functions (strncpy, strcat), don't yet
place a limit on reads from the source based on __builtin_object_size of
the source buffer.
* Extending coverage to more string functions like strlcat.
* It should be possible to optionally use __builtin_object_size(x, 1) for
some functions (C strings) to detect intra-object overflows (like
glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
approach to avoid likely compatibility issues.
* The compile-time checks should be made available via a separate config
option which can be enabled by default (or always enabled) once enough
time has passed to get the issues it catches fixed.
Kees said:
"This is great to have. While it was out-of-tree code, it would have
blocked at least CVE-2016-3858 from being exploitable (improper size
argument to strlcpy()). I've sent a number of fixes for
out-of-bounds-reads that this detected upstream already"
[arnd@arndb.de: x86: fix fortified memcpy]
Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-07-12 21:36:10 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan);
|
|
|
|
__FORTIFY_INLINE void *memscan(void *p, int c, __kernel_size_t size)
|
|
|
|
{
|
|
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
|
|
if (__builtin_constant_p(size) && p_size < size)
|
|
|
|
__read_overflow();
|
|
|
|
if (p_size < size)
|
|
|
|
fortify_panic(__func__);
|
|
|
|
return __real_memscan(p, c, size);
|
|
|
|
}
|
|
|
|
|
|
|
|
__FORTIFY_INLINE int memcmp(const void *p, const void *q, __kernel_size_t size)
|
|
|
|
{
|
|
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
|
|
size_t q_size = __builtin_object_size(q, 0);
|
|
|
|
if (__builtin_constant_p(size)) {
|
|
|
|
if (p_size < size)
|
|
|
|
__read_overflow();
|
|
|
|
if (q_size < size)
|
|
|
|
__read_overflow2();
|
|
|
|
}
|
|
|
|
if (p_size < size || q_size < size)
|
|
|
|
fortify_panic(__func__);
|
string.h: fix incompatibility between FORTIFY_SOURCE and KASAN
The memcmp KASAN self-test fails on a kernel with both KASAN and
FORTIFY_SOURCE.
When FORTIFY_SOURCE is on, a number of functions are replaced with
fortified versions, which attempt to check the sizes of the operands.
However, these functions often directly invoke __builtin_foo() once they
have performed the fortify check. Using __builtins may bypass KASAN
checks if the compiler decides to inline it's own implementation as
sequence of instructions, rather than emit a function call that goes out
to a KASAN-instrumented implementation.
Why is only memcmp affected?
============================
Of the string and string-like functions that kasan_test tests, only memcmp
is replaced by an inline sequence of instructions in my testing on x86
with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2).
I believe this is due to compiler heuristics. For example, if I annotate
kmalloc calls with the alloc_size annotation (and disable some fortify
compile-time checking!), the compiler will replace every memset except the
one in kmalloc_uaf_memset with inline instructions. (I have some WIP
patches to add this annotation.)
Does this affect other functions in string.h?
=============================================
Yes. Anything that uses __builtin_* rather than __real_* could be
affected. This looks like:
- strncpy
- strcat
- strlen
- strlcpy maybe, under some circumstances?
- strncat under some circumstances
- memset
- memcpy
- memmove
- memcmp (as noted)
- memchr
- strcpy
Whether a function call is emitted always depends on the compiler. Most
bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows
that this is not always the case.
Isn't FORTIFY_SOURCE disabled with KASAN?
========================================-
The string headers on all arches supporting KASAN disable fortify with
kasan, but only when address sanitisation is _also_ disabled. For example
from x86:
#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
/*
* For files that are not instrumented (e.g. mm/slub.c) we
* should use not instrumented version of mem* functions.
*/
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
#ifndef __NO_FORTIFY
#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
#endif
#endif
This comes from commit 6974f0c4555e ("include/linux/string.h: add the
option of fortified string.h functions"), and doesn't work when KASAN is
enabled and the file is supposed to be sanitised - as with test_kasan.c
I'm pretty sure this is not wrong, but not as expansive it should be:
* we shouldn't use __builtin_memcpy etc in files where we don't have
instrumentation - it could devolve into a function call to memcpy,
which will be instrumented. Rather, we should use __memcpy which
by convention is not instrumented.
* we also shouldn't be using __builtin_memcpy when we have a KASAN
instrumented file, because it could be replaced with inline asm
that will not be instrumented.
What is correct behaviour?
==========================
Firstly, there is some overlap between fortification and KASAN: both
provide some level of _runtime_ checking. Only fortify provides
compile-time checking.
KASAN and fortify can pick up different things at runtime:
- Some fortify functions, notably the string functions, could easily be
modified to consider sub-object sizes (e.g. members within a struct),
and I have some WIP patches to do this. KASAN cannot detect these
because it cannot insert poision between members of a struct.
- KASAN can detect many over-reads/over-writes when the sizes of both
operands are unknown, which fortify cannot.
So there are a couple of options:
1) Flip the test: disable fortify in santised files and enable it in
unsanitised files. This at least stops us missing KASAN checking, but
we lose the fortify checking.
2) Make the fortify code always call out to real versions. Do this only
for KASAN, for fear of losing the inlining opportunities we get from
__builtin_*.
(We can't use kasan_check_{read,write}: because the fortify functions are
_extern inline_, you can't include _static_ inline functions without a
compiler warning. kasan_check_{read,write} are static inline so we can't
use them even when they would otherwise be suitable.)
Take approach 2 and call out to real versions when KASAN is enabled.
Use __underlying_foo to distinguish from __real_foo: __real_foo always
refers to the kernel's implementation of foo, __underlying_foo could be
either the kernel implementation or the __builtin_foo implementation.
This is sometimes enough to make the memcmp test succeed with
FORTIFY_SOURCE enabled. It is at least enough to get the function call
into the module. One more fix is needed to make it reliable: see the next
patch.
Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions")
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Link: http://lkml.kernel.org/r/20200423154503.5103-3-dja@axtens.net
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-03 22:56:46 +00:00
|
|
|
return __underlying_memcmp(p, q, size);
|
include/linux/string.h: add the option of fortified string.h functions
This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time. Unlike glibc,
it covers buffer reads in addition to writes.
GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation. They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks. Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.
This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code. There will likely be issues caught in
regular use at runtime too.
Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:
* Some of the fortified string functions (strncpy, strcat), don't yet
place a limit on reads from the source based on __builtin_object_size of
the source buffer.
* Extending coverage to more string functions like strlcat.
* It should be possible to optionally use __builtin_object_size(x, 1) for
some functions (C strings) to detect intra-object overflows (like
glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
approach to avoid likely compatibility issues.
* The compile-time checks should be made available via a separate config
option which can be enabled by default (or always enabled) once enough
time has passed to get the issues it catches fixed.
Kees said:
"This is great to have. While it was out-of-tree code, it would have
blocked at least CVE-2016-3858 from being exploitable (improper size
argument to strlcpy()). I've sent a number of fixes for
out-of-bounds-reads that this detected upstream already"
[arnd@arndb.de: x86: fix fortified memcpy]
Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-07-12 21:36:10 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
__FORTIFY_INLINE void *memchr(const void *p, int c, __kernel_size_t size)
|
|
|
|
{
|
|
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
|
|
if (__builtin_constant_p(size) && p_size < size)
|
|
|
|
__read_overflow();
|
|
|
|
if (p_size < size)
|
|
|
|
fortify_panic(__func__);
|
string.h: fix incompatibility between FORTIFY_SOURCE and KASAN
The memcmp KASAN self-test fails on a kernel with both KASAN and
FORTIFY_SOURCE.
When FORTIFY_SOURCE is on, a number of functions are replaced with
fortified versions, which attempt to check the sizes of the operands.
However, these functions often directly invoke __builtin_foo() once they
have performed the fortify check. Using __builtins may bypass KASAN
checks if the compiler decides to inline it's own implementation as
sequence of instructions, rather than emit a function call that goes out
to a KASAN-instrumented implementation.
Why is only memcmp affected?
============================
Of the string and string-like functions that kasan_test tests, only memcmp
is replaced by an inline sequence of instructions in my testing on x86
with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2).
I believe this is due to compiler heuristics. For example, if I annotate
kmalloc calls with the alloc_size annotation (and disable some fortify
compile-time checking!), the compiler will replace every memset except the
one in kmalloc_uaf_memset with inline instructions. (I have some WIP
patches to add this annotation.)
Does this affect other functions in string.h?
=============================================
Yes. Anything that uses __builtin_* rather than __real_* could be
affected. This looks like:
- strncpy
- strcat
- strlen
- strlcpy maybe, under some circumstances?
- strncat under some circumstances
- memset
- memcpy
- memmove
- memcmp (as noted)
- memchr
- strcpy
Whether a function call is emitted always depends on the compiler. Most
bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows
that this is not always the case.
Isn't FORTIFY_SOURCE disabled with KASAN?
========================================-
The string headers on all arches supporting KASAN disable fortify with
kasan, but only when address sanitisation is _also_ disabled. For example
from x86:
#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
/*
* For files that are not instrumented (e.g. mm/slub.c) we
* should use not instrumented version of mem* functions.
*/
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
#ifndef __NO_FORTIFY
#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
#endif
#endif
This comes from commit 6974f0c4555e ("include/linux/string.h: add the
option of fortified string.h functions"), and doesn't work when KASAN is
enabled and the file is supposed to be sanitised - as with test_kasan.c
I'm pretty sure this is not wrong, but not as expansive it should be:
* we shouldn't use __builtin_memcpy etc in files where we don't have
instrumentation - it could devolve into a function call to memcpy,
which will be instrumented. Rather, we should use __memcpy which
by convention is not instrumented.
* we also shouldn't be using __builtin_memcpy when we have a KASAN
instrumented file, because it could be replaced with inline asm
that will not be instrumented.
What is correct behaviour?
==========================
Firstly, there is some overlap between fortification and KASAN: both
provide some level of _runtime_ checking. Only fortify provides
compile-time checking.
KASAN and fortify can pick up different things at runtime:
- Some fortify functions, notably the string functions, could easily be
modified to consider sub-object sizes (e.g. members within a struct),
and I have some WIP patches to do this. KASAN cannot detect these
because it cannot insert poision between members of a struct.
- KASAN can detect many over-reads/over-writes when the sizes of both
operands are unknown, which fortify cannot.
So there are a couple of options:
1) Flip the test: disable fortify in santised files and enable it in
unsanitised files. This at least stops us missing KASAN checking, but
we lose the fortify checking.
2) Make the fortify code always call out to real versions. Do this only
for KASAN, for fear of losing the inlining opportunities we get from
__builtin_*.
(We can't use kasan_check_{read,write}: because the fortify functions are
_extern inline_, you can't include _static_ inline functions without a
compiler warning. kasan_check_{read,write} are static inline so we can't
use them even when they would otherwise be suitable.)
Take approach 2 and call out to real versions when KASAN is enabled.
Use __underlying_foo to distinguish from __real_foo: __real_foo always
refers to the kernel's implementation of foo, __underlying_foo could be
either the kernel implementation or the __builtin_foo implementation.
This is sometimes enough to make the memcmp test succeed with
FORTIFY_SOURCE enabled. It is at least enough to get the function call
into the module. One more fix is needed to make it reliable: see the next
patch.
Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions")
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Link: http://lkml.kernel.org/r/20200423154503.5103-3-dja@axtens.net
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-03 22:56:46 +00:00
|
|
|
return __underlying_memchr(p, c, size);
|
include/linux/string.h: add the option of fortified string.h functions
This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time. Unlike glibc,
it covers buffer reads in addition to writes.
GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation. They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks. Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.
This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code. There will likely be issues caught in
regular use at runtime too.
Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:
* Some of the fortified string functions (strncpy, strcat), don't yet
place a limit on reads from the source based on __builtin_object_size of
the source buffer.
* Extending coverage to more string functions like strlcat.
* It should be possible to optionally use __builtin_object_size(x, 1) for
some functions (C strings) to detect intra-object overflows (like
glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
approach to avoid likely compatibility issues.
* The compile-time checks should be made available via a separate config
option which can be enabled by default (or always enabled) once enough
time has passed to get the issues it catches fixed.
Kees said:
"This is great to have. While it was out-of-tree code, it would have
blocked at least CVE-2016-3858 from being exploitable (improper size
argument to strlcpy()). I've sent a number of fixes for
out-of-bounds-reads that this detected upstream already"
[arnd@arndb.de: x86: fix fortified memcpy]
Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-07-12 21:36:10 +00:00
|
|
|
}
|
|
|
|
|
|
|
|
void *__real_memchr_inv(const void *s, int c, size_t n) __RENAME(memchr_inv);
|
|
|
|
__FORTIFY_INLINE void *memchr_inv(const void *p, int c, size_t size)
|
|
|
|
{
|
|
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
|
|
if (__builtin_constant_p(size) && p_size < size)
|
|
|
|
__read_overflow();
|
|
|
|
if (p_size < size)
|
|
|
|
fortify_panic(__func__);
|
|
|
|
return __real_memchr_inv(p, c, size);
|
|
|
|
}
|
|
|
|
|
|
|
|
extern void *__real_kmemdup(const void *src, size_t len, gfp_t gfp) __RENAME(kmemdup);
|
|
|
|
__FORTIFY_INLINE void *kmemdup(const void *p, size_t size, gfp_t gfp)
|
|
|
|
{
|
|
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
|
|
if (__builtin_constant_p(size) && p_size < size)
|
|
|
|
__read_overflow();
|
|
|
|
if (p_size < size)
|
|
|
|
fortify_panic(__func__);
|
|
|
|
return __real_kmemdup(p, size, gfp);
|
|
|
|
}
|
2017-07-14 21:28:12 +00:00
|
|
|
|
|
|
|
/* defined after fortified strlen and memcpy to reuse them */
|
|
|
|
__FORTIFY_INLINE char *strcpy(char *p, const char *q)
|
|
|
|
{
|
|
|
|
size_t p_size = __builtin_object_size(p, 0);
|
|
|
|
size_t q_size = __builtin_object_size(q, 0);
|
|
|
|
if (p_size == (size_t)-1 && q_size == (size_t)-1)
|
string.h: fix incompatibility between FORTIFY_SOURCE and KASAN
The memcmp KASAN self-test fails on a kernel with both KASAN and
FORTIFY_SOURCE.
When FORTIFY_SOURCE is on, a number of functions are replaced with
fortified versions, which attempt to check the sizes of the operands.
However, these functions often directly invoke __builtin_foo() once they
have performed the fortify check. Using __builtins may bypass KASAN
checks if the compiler decides to inline it's own implementation as
sequence of instructions, rather than emit a function call that goes out
to a KASAN-instrumented implementation.
Why is only memcmp affected?
============================
Of the string and string-like functions that kasan_test tests, only memcmp
is replaced by an inline sequence of instructions in my testing on x86
with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2).
I believe this is due to compiler heuristics. For example, if I annotate
kmalloc calls with the alloc_size annotation (and disable some fortify
compile-time checking!), the compiler will replace every memset except the
one in kmalloc_uaf_memset with inline instructions. (I have some WIP
patches to add this annotation.)
Does this affect other functions in string.h?
=============================================
Yes. Anything that uses __builtin_* rather than __real_* could be
affected. This looks like:
- strncpy
- strcat
- strlen
- strlcpy maybe, under some circumstances?
- strncat under some circumstances
- memset
- memcpy
- memmove
- memcmp (as noted)
- memchr
- strcpy
Whether a function call is emitted always depends on the compiler. Most
bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows
that this is not always the case.
Isn't FORTIFY_SOURCE disabled with KASAN?
========================================-
The string headers on all arches supporting KASAN disable fortify with
kasan, but only when address sanitisation is _also_ disabled. For example
from x86:
#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
/*
* For files that are not instrumented (e.g. mm/slub.c) we
* should use not instrumented version of mem* functions.
*/
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
#ifndef __NO_FORTIFY
#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
#endif
#endif
This comes from commit 6974f0c4555e ("include/linux/string.h: add the
option of fortified string.h functions"), and doesn't work when KASAN is
enabled and the file is supposed to be sanitised - as with test_kasan.c
I'm pretty sure this is not wrong, but not as expansive it should be:
* we shouldn't use __builtin_memcpy etc in files where we don't have
instrumentation - it could devolve into a function call to memcpy,
which will be instrumented. Rather, we should use __memcpy which
by convention is not instrumented.
* we also shouldn't be using __builtin_memcpy when we have a KASAN
instrumented file, because it could be replaced with inline asm
that will not be instrumented.
What is correct behaviour?
==========================
Firstly, there is some overlap between fortification and KASAN: both
provide some level of _runtime_ checking. Only fortify provides
compile-time checking.
KASAN and fortify can pick up different things at runtime:
- Some fortify functions, notably the string functions, could easily be
modified to consider sub-object sizes (e.g. members within a struct),
and I have some WIP patches to do this. KASAN cannot detect these
because it cannot insert poision between members of a struct.
- KASAN can detect many over-reads/over-writes when the sizes of both
operands are unknown, which fortify cannot.
So there are a couple of options:
1) Flip the test: disable fortify in santised files and enable it in
unsanitised files. This at least stops us missing KASAN checking, but
we lose the fortify checking.
2) Make the fortify code always call out to real versions. Do this only
for KASAN, for fear of losing the inlining opportunities we get from
__builtin_*.
(We can't use kasan_check_{read,write}: because the fortify functions are
_extern inline_, you can't include _static_ inline functions without a
compiler warning. kasan_check_{read,write} are static inline so we can't
use them even when they would otherwise be suitable.)
Take approach 2 and call out to real versions when KASAN is enabled.
Use __underlying_foo to distinguish from __real_foo: __real_foo always
refers to the kernel's implementation of foo, __underlying_foo could be
either the kernel implementation or the __builtin_foo implementation.
This is sometimes enough to make the memcmp test succeed with
FORTIFY_SOURCE enabled. It is at least enough to get the function call
into the module. One more fix is needed to make it reliable: see the next
patch.
Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions")
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Link: http://lkml.kernel.org/r/20200423154503.5103-3-dja@axtens.net
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-03 22:56:46 +00:00
|
|
|
return __underlying_strcpy(p, q);
|
2017-07-14 21:28:12 +00:00
|
|
|
memcpy(p, q, strlen(q) + 1);
|
|
|
|
return p;
|
|
|
|
}
|
|
|
|
|
string.h: fix incompatibility between FORTIFY_SOURCE and KASAN
The memcmp KASAN self-test fails on a kernel with both KASAN and
FORTIFY_SOURCE.
When FORTIFY_SOURCE is on, a number of functions are replaced with
fortified versions, which attempt to check the sizes of the operands.
However, these functions often directly invoke __builtin_foo() once they
have performed the fortify check. Using __builtins may bypass KASAN
checks if the compiler decides to inline it's own implementation as
sequence of instructions, rather than emit a function call that goes out
to a KASAN-instrumented implementation.
Why is only memcmp affected?
============================
Of the string and string-like functions that kasan_test tests, only memcmp
is replaced by an inline sequence of instructions in my testing on x86
with gcc version 9.2.1 20191008 (Ubuntu 9.2.1-9ubuntu2).
I believe this is due to compiler heuristics. For example, if I annotate
kmalloc calls with the alloc_size annotation (and disable some fortify
compile-time checking!), the compiler will replace every memset except the
one in kmalloc_uaf_memset with inline instructions. (I have some WIP
patches to add this annotation.)
Does this affect other functions in string.h?
=============================================
Yes. Anything that uses __builtin_* rather than __real_* could be
affected. This looks like:
- strncpy
- strcat
- strlen
- strlcpy maybe, under some circumstances?
- strncat under some circumstances
- memset
- memcpy
- memmove
- memcmp (as noted)
- memchr
- strcpy
Whether a function call is emitted always depends on the compiler. Most
bugs should get caught by FORTIFY_SOURCE, but the missed memcmp test shows
that this is not always the case.
Isn't FORTIFY_SOURCE disabled with KASAN?
========================================-
The string headers on all arches supporting KASAN disable fortify with
kasan, but only when address sanitisation is _also_ disabled. For example
from x86:
#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
/*
* For files that are not instrumented (e.g. mm/slub.c) we
* should use not instrumented version of mem* functions.
*/
#define memcpy(dst, src, len) __memcpy(dst, src, len)
#define memmove(dst, src, len) __memmove(dst, src, len)
#define memset(s, c, n) __memset(s, c, n)
#ifndef __NO_FORTIFY
#define __NO_FORTIFY /* FORTIFY_SOURCE uses __builtin_memcpy, etc. */
#endif
#endif
This comes from commit 6974f0c4555e ("include/linux/string.h: add the
option of fortified string.h functions"), and doesn't work when KASAN is
enabled and the file is supposed to be sanitised - as with test_kasan.c
I'm pretty sure this is not wrong, but not as expansive it should be:
* we shouldn't use __builtin_memcpy etc in files where we don't have
instrumentation - it could devolve into a function call to memcpy,
which will be instrumented. Rather, we should use __memcpy which
by convention is not instrumented.
* we also shouldn't be using __builtin_memcpy when we have a KASAN
instrumented file, because it could be replaced with inline asm
that will not be instrumented.
What is correct behaviour?
==========================
Firstly, there is some overlap between fortification and KASAN: both
provide some level of _runtime_ checking. Only fortify provides
compile-time checking.
KASAN and fortify can pick up different things at runtime:
- Some fortify functions, notably the string functions, could easily be
modified to consider sub-object sizes (e.g. members within a struct),
and I have some WIP patches to do this. KASAN cannot detect these
because it cannot insert poision between members of a struct.
- KASAN can detect many over-reads/over-writes when the sizes of both
operands are unknown, which fortify cannot.
So there are a couple of options:
1) Flip the test: disable fortify in santised files and enable it in
unsanitised files. This at least stops us missing KASAN checking, but
we lose the fortify checking.
2) Make the fortify code always call out to real versions. Do this only
for KASAN, for fear of losing the inlining opportunities we get from
__builtin_*.
(We can't use kasan_check_{read,write}: because the fortify functions are
_extern inline_, you can't include _static_ inline functions without a
compiler warning. kasan_check_{read,write} are static inline so we can't
use them even when they would otherwise be suitable.)
Take approach 2 and call out to real versions when KASAN is enabled.
Use __underlying_foo to distinguish from __real_foo: __real_foo always
refers to the kernel's implementation of foo, __underlying_foo could be
either the kernel implementation or the __builtin_foo implementation.
This is sometimes enough to make the memcmp test succeed with
FORTIFY_SOURCE enabled. It is at least enough to get the function call
into the module. One more fix is needed to make it reliable: see the next
patch.
Fixes: 6974f0c4555e ("include/linux/string.h: add the option of fortified string.h functions")
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: David Gow <davidgow@google.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Link: http://lkml.kernel.org/r/20200423154503.5103-3-dja@axtens.net
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-06-03 22:56:46 +00:00
|
|
|
/* Don't use these outside the FORITFY_SOURCE implementation */
|
|
|
|
#undef __underlying_memchr
|
|
|
|
#undef __underlying_memcmp
|
|
|
|
#undef __underlying_memcpy
|
|
|
|
#undef __underlying_memmove
|
|
|
|
#undef __underlying_memset
|
|
|
|
#undef __underlying_strcat
|
|
|
|
#undef __underlying_strcpy
|
|
|
|
#undef __underlying_strlen
|
|
|
|
#undef __underlying_strncat
|
|
|
|
#undef __underlying_strncpy
|
include/linux/string.h: add the option of fortified string.h functions
This adds support for compiling with a rough equivalent to the glibc
_FORTIFY_SOURCE=1 feature, providing compile-time and runtime buffer
overflow checks for string.h functions when the compiler determines the
size of the source or destination buffer at compile-time. Unlike glibc,
it covers buffer reads in addition to writes.
GNU C __builtin_*_chk intrinsics are avoided because they would force a
much more complex implementation. They aren't designed to detect read
overflows and offer no real benefit when using an implementation based
on inline checks. Inline checks don't add up to much code size and
allow full use of the regular string intrinsics while avoiding the need
for a bunch of _chk functions and per-arch assembly to avoid wrapper
overhead.
This detects various overflows at compile-time in various drivers and
some non-x86 core kernel code. There will likely be issues caught in
regular use at runtime too.
Future improvements left out of initial implementation for simplicity,
as it's all quite optional and can be done incrementally:
* Some of the fortified string functions (strncpy, strcat), don't yet
place a limit on reads from the source based on __builtin_object_size of
the source buffer.
* Extending coverage to more string functions like strlcat.
* It should be possible to optionally use __builtin_object_size(x, 1) for
some functions (C strings) to detect intra-object overflows (like
glibc's _FORTIFY_SOURCE=2), but for now this takes the conservative
approach to avoid likely compatibility issues.
* The compile-time checks should be made available via a separate config
option which can be enabled by default (or always enabled) once enough
time has passed to get the issues it catches fixed.
Kees said:
"This is great to have. While it was out-of-tree code, it would have
blocked at least CVE-2016-3858 from being exploitable (improper size
argument to strlcpy()). I've sent a number of fixes for
out-of-bounds-reads that this detected upstream already"
[arnd@arndb.de: x86: fix fortified memcpy]
Link: http://lkml.kernel.org/r/20170627150047.660360-1-arnd@arndb.de
[keescook@chromium.org: avoid panic() in favor of BUG()]
Link: http://lkml.kernel.org/r/20170626235122.GA25261@beast
[keescook@chromium.org: move from -mm, add ARCH_HAS_FORTIFY_SOURCE, tweak Kconfig help]
Link: http://lkml.kernel.org/r/20170526095404.20439-1-danielmicay@gmail.com
Link: http://lkml.kernel.org/r/1497903987-21002-8-git-send-email-keescook@chromium.org
Signed-off-by: Daniel Micay <danielmicay@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-07-12 21:36:10 +00:00
|
|
|
#endif
|
|
|
|
|
2017-08-14 20:12:38 +00:00
|
|
|
/**
|
|
|
|
* memcpy_and_pad - Copy one buffer to another with padding
|
|
|
|
* @dest: Where to copy to
|
|
|
|
* @dest_len: The destination buffer size
|
|
|
|
* @src: Where to copy from
|
|
|
|
* @count: The number of bytes to copy
|
|
|
|
* @pad: Character to use for padding if space is left in destination.
|
|
|
|
*/
|
2017-09-06 12:36:57 +00:00
|
|
|
static inline void memcpy_and_pad(void *dest, size_t dest_len,
|
|
|
|
const void *src, size_t count, int pad)
|
2017-08-14 20:12:38 +00:00
|
|
|
{
|
|
|
|
if (dest_len > count) {
|
|
|
|
memcpy(dest, src, count);
|
|
|
|
memset(dest + count, pad, dest_len - count);
|
|
|
|
} else
|
|
|
|
memcpy(dest, src, dest_len);
|
|
|
|
}
|
|
|
|
|
string.h: Add str_has_prefix() helper function
A discussion came up in the trace triggers thread about converting a
bunch of:
strncmp(str, "const", sizeof("const") - 1)
use cases into a helper macro. It started with:
strncmp(str, const, sizeof(const) - 1)
But then Joe Perches mentioned that if a const is not used, the
sizeof() will be the size of a pointer, which can be bad. And that
gcc will optimize strlen("const") into "sizeof("const") - 1".
Thinking about this more, a quick grep in the kernel tree found several
(thousands!) of cases that use this construct. A quick grep also
revealed that there's probably several bugs in that use case. Some are
that people forgot the "- 1" (which I found) and others could be that
the constant for the sizeof is different than the constant (although, I
haven't found any of those, but I also didn't look hard).
I figured the best thing to do is to create a helper macro and place it
into include/linux/string.h. And go around and fix all the open coded
versions of it later.
Note, gcc appears to optimize this when we make it into an always_inline
static function, which removes a lot of issues that a macro produces.
Link: http://lkml.kernel.org/r/e3e754f2bd18e56eaa8baf79bee619316ebf4cfc.1545161087.git.tom.zanussi@linux.intel.com
Link: http://lkml.kernel.org/r/20181219211615.2298e781@gandalf.local.home
Link: http://lkml.kernel.org/r/CAHk-=wg_sR-UEC1ggmkZpypOUYanL5CMX4R7ceuaV4QMf5jBtg@mail.gmail.com
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Suggestions-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggestions-by: Joe Perches <joe@perches.com>
Suggestions-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
2018-12-21 23:10:14 +00:00
|
|
|
/**
|
|
|
|
* str_has_prefix - Test if a string has a given prefix
|
|
|
|
* @str: The string to test
|
|
|
|
* @prefix: The string to see if @str starts with
|
|
|
|
*
|
|
|
|
* A common way to test a prefix of a string is to do:
|
|
|
|
* strncmp(str, prefix, sizeof(prefix) - 1)
|
|
|
|
*
|
|
|
|
* But this can lead to bugs due to typos, or if prefix is a pointer
|
|
|
|
* and not a constant. Instead use str_has_prefix().
|
|
|
|
*
|
2019-09-25 23:46:13 +00:00
|
|
|
* Returns:
|
|
|
|
* * strlen(@prefix) if @str starts with @prefix
|
|
|
|
* * 0 if @str does not start with @prefix
|
string.h: Add str_has_prefix() helper function
A discussion came up in the trace triggers thread about converting a
bunch of:
strncmp(str, "const", sizeof("const") - 1)
use cases into a helper macro. It started with:
strncmp(str, const, sizeof(const) - 1)
But then Joe Perches mentioned that if a const is not used, the
sizeof() will be the size of a pointer, which can be bad. And that
gcc will optimize strlen("const") into "sizeof("const") - 1".
Thinking about this more, a quick grep in the kernel tree found several
(thousands!) of cases that use this construct. A quick grep also
revealed that there's probably several bugs in that use case. Some are
that people forgot the "- 1" (which I found) and others could be that
the constant for the sizeof is different than the constant (although, I
haven't found any of those, but I also didn't look hard).
I figured the best thing to do is to create a helper macro and place it
into include/linux/string.h. And go around and fix all the open coded
versions of it later.
Note, gcc appears to optimize this when we make it into an always_inline
static function, which removes a lot of issues that a macro produces.
Link: http://lkml.kernel.org/r/e3e754f2bd18e56eaa8baf79bee619316ebf4cfc.1545161087.git.tom.zanussi@linux.intel.com
Link: http://lkml.kernel.org/r/20181219211615.2298e781@gandalf.local.home
Link: http://lkml.kernel.org/r/CAHk-=wg_sR-UEC1ggmkZpypOUYanL5CMX4R7ceuaV4QMf5jBtg@mail.gmail.com
Cc: Tom Zanussi <zanussi@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Suggestions-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggestions-by: Joe Perches <joe@perches.com>
Suggestions-by: Andreas Schwab <schwab@linux-m68k.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
2018-12-21 23:10:14 +00:00
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*/
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static __always_inline size_t str_has_prefix(const char *str, const char *prefix)
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{
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size_t len = strlen(prefix);
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return strncmp(str, prefix, len) == 0 ? len : 0;
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}
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2005-04-16 22:20:36 +00:00
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#endif /* _LINUX_STRING_H_ */
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