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
|
|
|
/* SPDX-License-Identifier: GPL-2.0 */
|
kasan: add kernel address sanitizer infrastructure
Kernel Address sanitizer (KASan) is a dynamic memory error detector. It
provides fast and comprehensive solution for finding use-after-free and
out-of-bounds bugs.
KASAN uses compile-time instrumentation for checking every memory access,
therefore GCC > v4.9.2 required. v4.9.2 almost works, but has issues with
putting symbol aliases into the wrong section, which breaks kasan
instrumentation of globals.
This patch only adds infrastructure for kernel address sanitizer. It's
not available for use yet. The idea and some code was borrowed from [1].
Basic idea:
The main idea of KASAN is to use shadow memory to record whether each byte
of memory is safe to access or not, and use compiler's instrumentation to
check the shadow memory on each memory access.
Address sanitizer uses 1/8 of the memory addressable in kernel for shadow
memory and uses direct mapping with a scale and offset to translate a
memory address to its corresponding shadow address.
Here is function to translate address to corresponding shadow address:
unsigned long kasan_mem_to_shadow(unsigned long addr)
{
return (addr >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET;
}
where KASAN_SHADOW_SCALE_SHIFT = 3.
So for every 8 bytes there is one corresponding byte of shadow memory.
The following encoding used for each shadow byte: 0 means that all 8 bytes
of the corresponding memory region are valid for access; k (1 <= k <= 7)
means that the first k bytes are valid for access, and other (8 - k) bytes
are not; Any negative value indicates that the entire 8-bytes are
inaccessible. Different negative values used to distinguish between
different kinds of inaccessible memory (redzones, freed memory) (see
mm/kasan/kasan.h).
To be able to detect accesses to bad memory we need a special compiler.
Such compiler inserts a specific function calls (__asan_load*(addr),
__asan_store*(addr)) before each memory access of size 1, 2, 4, 8 or 16.
These functions check whether memory region is valid to access or not by
checking corresponding shadow memory. If access is not valid an error
printed.
Historical background of the address sanitizer from Dmitry Vyukov:
"We've developed the set of tools, AddressSanitizer (Asan),
ThreadSanitizer and MemorySanitizer, for user space. We actively use
them for testing inside of Google (continuous testing, fuzzing,
running prod services). To date the tools have found more than 10'000
scary bugs in Chromium, Google internal codebase and various
open-source projects (Firefox, OpenSSL, gcc, clang, ffmpeg, MySQL and
lots of others): [2] [3] [4].
The tools are part of both gcc and clang compilers.
We have not yet done massive testing under the Kernel AddressSanitizer
(it's kind of chicken and egg problem, you need it to be upstream to
start applying it extensively). To date it has found about 50 bugs.
Bugs that we've found in upstream kernel are listed in [5].
We've also found ~20 bugs in out internal version of the kernel. Also
people from Samsung and Oracle have found some.
[...]
As others noted, the main feature of AddressSanitizer is its
performance due to inline compiler instrumentation and simple linear
shadow memory. User-space Asan has ~2x slowdown on computational
programs and ~2x memory consumption increase. Taking into account that
kernel usually consumes only small fraction of CPU and memory when
running real user-space programs, I would expect that kernel Asan will
have ~10-30% slowdown and similar memory consumption increase (when we
finish all tuning).
I agree that Asan can well replace kmemcheck. We have plans to start
working on Kernel MemorySanitizer that finds uses of unitialized
memory. Asan+Msan will provide feature-parity with kmemcheck. As
others noted, Asan will unlikely replace debug slab and pagealloc that
can be enabled at runtime. Asan uses compiler instrumentation, so even
if it is disabled, it still incurs visible overheads.
Asan technology is easily portable to other architectures. Compiler
instrumentation is fully portable. Runtime has some arch-dependent
parts like shadow mapping and atomic operation interception. They are
relatively easy to port."
Comparison with other debugging features:
========================================
KMEMCHECK:
- KASan can do almost everything that kmemcheck can. KASan uses
compile-time instrumentation, which makes it significantly faster than
kmemcheck. The only advantage of kmemcheck over KASan is detection of
uninitialized memory reads.
Some brief performance testing showed that kasan could be
x500-x600 times faster than kmemcheck:
$ netperf -l 30
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost (127.0.0.1) port 0 AF_INET
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec
no debug: 87380 16384 16384 30.00 41624.72
kasan inline: 87380 16384 16384 30.00 12870.54
kasan outline: 87380 16384 16384 30.00 10586.39
kmemcheck: 87380 16384 16384 30.03 20.23
- Also kmemcheck couldn't work on several CPUs. It always sets
number of CPUs to 1. KASan doesn't have such limitation.
DEBUG_PAGEALLOC:
- KASan is slower than DEBUG_PAGEALLOC, but KASan works on sub-page
granularity level, so it able to find more bugs.
SLUB_DEBUG (poisoning, redzones):
- SLUB_DEBUG has lower overhead than KASan.
- SLUB_DEBUG in most cases are not able to detect bad reads,
KASan able to detect both reads and writes.
- In some cases (e.g. redzone overwritten) SLUB_DEBUG detect
bugs only on allocation/freeing of object. KASan catch
bugs right before it will happen, so we always know exact
place of first bad read/write.
[1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel
[2] https://code.google.com/p/address-sanitizer/wiki/FoundBugs
[3] https://code.google.com/p/thread-sanitizer/wiki/FoundBugs
[4] https://code.google.com/p/memory-sanitizer/wiki/FoundBugs
[5] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel#Trophies
Based on work by Andrey Konovalov.
Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Acked-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrey Konovalov <adech.fo@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Serebryany <kcc@google.com>
Cc: Dmitry Chernenkov <dmitryc@google.com>
Cc: Yuri Gribov <tetra2005@gmail.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-13 22:39:17 +00:00
|
|
|
#ifndef _LINUX_KASAN_H
|
|
|
|
|
#define _LINUX_KASAN_H
|
|
|
|
|
|
2020-12-22 20:03:10 +00:00
|
|
|
#include <linux/static_key.h>
|
kasan: add kernel address sanitizer infrastructure
Kernel Address sanitizer (KASan) is a dynamic memory error detector. It
provides fast and comprehensive solution for finding use-after-free and
out-of-bounds bugs.
KASAN uses compile-time instrumentation for checking every memory access,
therefore GCC > v4.9.2 required. v4.9.2 almost works, but has issues with
putting symbol aliases into the wrong section, which breaks kasan
instrumentation of globals.
This patch only adds infrastructure for kernel address sanitizer. It's
not available for use yet. The idea and some code was borrowed from [1].
Basic idea:
The main idea of KASAN is to use shadow memory to record whether each byte
of memory is safe to access or not, and use compiler's instrumentation to
check the shadow memory on each memory access.
Address sanitizer uses 1/8 of the memory addressable in kernel for shadow
memory and uses direct mapping with a scale and offset to translate a
memory address to its corresponding shadow address.
Here is function to translate address to corresponding shadow address:
unsigned long kasan_mem_to_shadow(unsigned long addr)
{
return (addr >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET;
}
where KASAN_SHADOW_SCALE_SHIFT = 3.
So for every 8 bytes there is one corresponding byte of shadow memory.
The following encoding used for each shadow byte: 0 means that all 8 bytes
of the corresponding memory region are valid for access; k (1 <= k <= 7)
means that the first k bytes are valid for access, and other (8 - k) bytes
are not; Any negative value indicates that the entire 8-bytes are
inaccessible. Different negative values used to distinguish between
different kinds of inaccessible memory (redzones, freed memory) (see
mm/kasan/kasan.h).
To be able to detect accesses to bad memory we need a special compiler.
Such compiler inserts a specific function calls (__asan_load*(addr),
__asan_store*(addr)) before each memory access of size 1, 2, 4, 8 or 16.
These functions check whether memory region is valid to access or not by
checking corresponding shadow memory. If access is not valid an error
printed.
Historical background of the address sanitizer from Dmitry Vyukov:
"We've developed the set of tools, AddressSanitizer (Asan),
ThreadSanitizer and MemorySanitizer, for user space. We actively use
them for testing inside of Google (continuous testing, fuzzing,
running prod services). To date the tools have found more than 10'000
scary bugs in Chromium, Google internal codebase and various
open-source projects (Firefox, OpenSSL, gcc, clang, ffmpeg, MySQL and
lots of others): [2] [3] [4].
The tools are part of both gcc and clang compilers.
We have not yet done massive testing under the Kernel AddressSanitizer
(it's kind of chicken and egg problem, you need it to be upstream to
start applying it extensively). To date it has found about 50 bugs.
Bugs that we've found in upstream kernel are listed in [5].
We've also found ~20 bugs in out internal version of the kernel. Also
people from Samsung and Oracle have found some.
[...]
As others noted, the main feature of AddressSanitizer is its
performance due to inline compiler instrumentation and simple linear
shadow memory. User-space Asan has ~2x slowdown on computational
programs and ~2x memory consumption increase. Taking into account that
kernel usually consumes only small fraction of CPU and memory when
running real user-space programs, I would expect that kernel Asan will
have ~10-30% slowdown and similar memory consumption increase (when we
finish all tuning).
I agree that Asan can well replace kmemcheck. We have plans to start
working on Kernel MemorySanitizer that finds uses of unitialized
memory. Asan+Msan will provide feature-parity with kmemcheck. As
others noted, Asan will unlikely replace debug slab and pagealloc that
can be enabled at runtime. Asan uses compiler instrumentation, so even
if it is disabled, it still incurs visible overheads.
Asan technology is easily portable to other architectures. Compiler
instrumentation is fully portable. Runtime has some arch-dependent
parts like shadow mapping and atomic operation interception. They are
relatively easy to port."
Comparison with other debugging features:
========================================
KMEMCHECK:
- KASan can do almost everything that kmemcheck can. KASan uses
compile-time instrumentation, which makes it significantly faster than
kmemcheck. The only advantage of kmemcheck over KASan is detection of
uninitialized memory reads.
Some brief performance testing showed that kasan could be
x500-x600 times faster than kmemcheck:
$ netperf -l 30
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost (127.0.0.1) port 0 AF_INET
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec
no debug: 87380 16384 16384 30.00 41624.72
kasan inline: 87380 16384 16384 30.00 12870.54
kasan outline: 87380 16384 16384 30.00 10586.39
kmemcheck: 87380 16384 16384 30.03 20.23
- Also kmemcheck couldn't work on several CPUs. It always sets
number of CPUs to 1. KASan doesn't have such limitation.
DEBUG_PAGEALLOC:
- KASan is slower than DEBUG_PAGEALLOC, but KASan works on sub-page
granularity level, so it able to find more bugs.
SLUB_DEBUG (poisoning, redzones):
- SLUB_DEBUG has lower overhead than KASan.
- SLUB_DEBUG in most cases are not able to detect bad reads,
KASan able to detect both reads and writes.
- In some cases (e.g. redzone overwritten) SLUB_DEBUG detect
bugs only on allocation/freeing of object. KASan catch
bugs right before it will happen, so we always know exact
place of first bad read/write.
[1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel
[2] https://code.google.com/p/address-sanitizer/wiki/FoundBugs
[3] https://code.google.com/p/thread-sanitizer/wiki/FoundBugs
[4] https://code.google.com/p/memory-sanitizer/wiki/FoundBugs
[5] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel#Trophies
Based on work by Andrey Konovalov.
Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Acked-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrey Konovalov <adech.fo@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Serebryany <kcc@google.com>
Cc: Dmitry Chernenkov <dmitryc@google.com>
Cc: Yuri Gribov <tetra2005@gmail.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-13 22:39:17 +00:00
|
|
|
#include <linux/types.h>
|
|
|
|
|
|
|
|
|
|
struct kmem_cache;
|
|
|
|
|
struct page;
|
2015-03-12 23:26:11 +00:00
|
|
|
struct vm_struct;
|
2017-03-16 23:40:21 +00:00
|
|
|
struct task_struct;
|
kasan: add kernel address sanitizer infrastructure
Kernel Address sanitizer (KASan) is a dynamic memory error detector. It
provides fast and comprehensive solution for finding use-after-free and
out-of-bounds bugs.
KASAN uses compile-time instrumentation for checking every memory access,
therefore GCC > v4.9.2 required. v4.9.2 almost works, but has issues with
putting symbol aliases into the wrong section, which breaks kasan
instrumentation of globals.
This patch only adds infrastructure for kernel address sanitizer. It's
not available for use yet. The idea and some code was borrowed from [1].
Basic idea:
The main idea of KASAN is to use shadow memory to record whether each byte
of memory is safe to access or not, and use compiler's instrumentation to
check the shadow memory on each memory access.
Address sanitizer uses 1/8 of the memory addressable in kernel for shadow
memory and uses direct mapping with a scale and offset to translate a
memory address to its corresponding shadow address.
Here is function to translate address to corresponding shadow address:
unsigned long kasan_mem_to_shadow(unsigned long addr)
{
return (addr >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET;
}
where KASAN_SHADOW_SCALE_SHIFT = 3.
So for every 8 bytes there is one corresponding byte of shadow memory.
The following encoding used for each shadow byte: 0 means that all 8 bytes
of the corresponding memory region are valid for access; k (1 <= k <= 7)
means that the first k bytes are valid for access, and other (8 - k) bytes
are not; Any negative value indicates that the entire 8-bytes are
inaccessible. Different negative values used to distinguish between
different kinds of inaccessible memory (redzones, freed memory) (see
mm/kasan/kasan.h).
To be able to detect accesses to bad memory we need a special compiler.
Such compiler inserts a specific function calls (__asan_load*(addr),
__asan_store*(addr)) before each memory access of size 1, 2, 4, 8 or 16.
These functions check whether memory region is valid to access or not by
checking corresponding shadow memory. If access is not valid an error
printed.
Historical background of the address sanitizer from Dmitry Vyukov:
"We've developed the set of tools, AddressSanitizer (Asan),
ThreadSanitizer and MemorySanitizer, for user space. We actively use
them for testing inside of Google (continuous testing, fuzzing,
running prod services). To date the tools have found more than 10'000
scary bugs in Chromium, Google internal codebase and various
open-source projects (Firefox, OpenSSL, gcc, clang, ffmpeg, MySQL and
lots of others): [2] [3] [4].
The tools are part of both gcc and clang compilers.
We have not yet done massive testing under the Kernel AddressSanitizer
(it's kind of chicken and egg problem, you need it to be upstream to
start applying it extensively). To date it has found about 50 bugs.
Bugs that we've found in upstream kernel are listed in [5].
We've also found ~20 bugs in out internal version of the kernel. Also
people from Samsung and Oracle have found some.
[...]
As others noted, the main feature of AddressSanitizer is its
performance due to inline compiler instrumentation and simple linear
shadow memory. User-space Asan has ~2x slowdown on computational
programs and ~2x memory consumption increase. Taking into account that
kernel usually consumes only small fraction of CPU and memory when
running real user-space programs, I would expect that kernel Asan will
have ~10-30% slowdown and similar memory consumption increase (when we
finish all tuning).
I agree that Asan can well replace kmemcheck. We have plans to start
working on Kernel MemorySanitizer that finds uses of unitialized
memory. Asan+Msan will provide feature-parity with kmemcheck. As
others noted, Asan will unlikely replace debug slab and pagealloc that
can be enabled at runtime. Asan uses compiler instrumentation, so even
if it is disabled, it still incurs visible overheads.
Asan technology is easily portable to other architectures. Compiler
instrumentation is fully portable. Runtime has some arch-dependent
parts like shadow mapping and atomic operation interception. They are
relatively easy to port."
Comparison with other debugging features:
========================================
KMEMCHECK:
- KASan can do almost everything that kmemcheck can. KASan uses
compile-time instrumentation, which makes it significantly faster than
kmemcheck. The only advantage of kmemcheck over KASan is detection of
uninitialized memory reads.
Some brief performance testing showed that kasan could be
x500-x600 times faster than kmemcheck:
$ netperf -l 30
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost (127.0.0.1) port 0 AF_INET
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec
no debug: 87380 16384 16384 30.00 41624.72
kasan inline: 87380 16384 16384 30.00 12870.54
kasan outline: 87380 16384 16384 30.00 10586.39
kmemcheck: 87380 16384 16384 30.03 20.23
- Also kmemcheck couldn't work on several CPUs. It always sets
number of CPUs to 1. KASan doesn't have such limitation.
DEBUG_PAGEALLOC:
- KASan is slower than DEBUG_PAGEALLOC, but KASan works on sub-page
granularity level, so it able to find more bugs.
SLUB_DEBUG (poisoning, redzones):
- SLUB_DEBUG has lower overhead than KASan.
- SLUB_DEBUG in most cases are not able to detect bad reads,
KASan able to detect both reads and writes.
- In some cases (e.g. redzone overwritten) SLUB_DEBUG detect
bugs only on allocation/freeing of object. KASan catch
bugs right before it will happen, so we always know exact
place of first bad read/write.
[1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel
[2] https://code.google.com/p/address-sanitizer/wiki/FoundBugs
[3] https://code.google.com/p/thread-sanitizer/wiki/FoundBugs
[4] https://code.google.com/p/memory-sanitizer/wiki/FoundBugs
[5] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel#Trophies
Based on work by Andrey Konovalov.
Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Acked-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrey Konovalov <adech.fo@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Serebryany <kcc@google.com>
Cc: Dmitry Chernenkov <dmitryc@google.com>
Cc: Yuri Gribov <tetra2005@gmail.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-13 22:39:17 +00:00
|
|
|
|
|
|
|
|
#ifdef CONFIG_KASAN
|
|
|
|
|
|
2020-12-22 20:00:17 +00:00
|
|
|
#include <linux/linkage.h>
|
2020-06-09 04:32:42 +00:00
|
|
|
#include <asm/kasan.h>
|
kasan: add kernel address sanitizer infrastructure
Kernel Address sanitizer (KASan) is a dynamic memory error detector. It
provides fast and comprehensive solution for finding use-after-free and
out-of-bounds bugs.
KASAN uses compile-time instrumentation for checking every memory access,
therefore GCC > v4.9.2 required. v4.9.2 almost works, but has issues with
putting symbol aliases into the wrong section, which breaks kasan
instrumentation of globals.
This patch only adds infrastructure for kernel address sanitizer. It's
not available for use yet. The idea and some code was borrowed from [1].
Basic idea:
The main idea of KASAN is to use shadow memory to record whether each byte
of memory is safe to access or not, and use compiler's instrumentation to
check the shadow memory on each memory access.
Address sanitizer uses 1/8 of the memory addressable in kernel for shadow
memory and uses direct mapping with a scale and offset to translate a
memory address to its corresponding shadow address.
Here is function to translate address to corresponding shadow address:
unsigned long kasan_mem_to_shadow(unsigned long addr)
{
return (addr >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET;
}
where KASAN_SHADOW_SCALE_SHIFT = 3.
So for every 8 bytes there is one corresponding byte of shadow memory.
The following encoding used for each shadow byte: 0 means that all 8 bytes
of the corresponding memory region are valid for access; k (1 <= k <= 7)
means that the first k bytes are valid for access, and other (8 - k) bytes
are not; Any negative value indicates that the entire 8-bytes are
inaccessible. Different negative values used to distinguish between
different kinds of inaccessible memory (redzones, freed memory) (see
mm/kasan/kasan.h).
To be able to detect accesses to bad memory we need a special compiler.
Such compiler inserts a specific function calls (__asan_load*(addr),
__asan_store*(addr)) before each memory access of size 1, 2, 4, 8 or 16.
These functions check whether memory region is valid to access or not by
checking corresponding shadow memory. If access is not valid an error
printed.
Historical background of the address sanitizer from Dmitry Vyukov:
"We've developed the set of tools, AddressSanitizer (Asan),
ThreadSanitizer and MemorySanitizer, for user space. We actively use
them for testing inside of Google (continuous testing, fuzzing,
running prod services). To date the tools have found more than 10'000
scary bugs in Chromium, Google internal codebase and various
open-source projects (Firefox, OpenSSL, gcc, clang, ffmpeg, MySQL and
lots of others): [2] [3] [4].
The tools are part of both gcc and clang compilers.
We have not yet done massive testing under the Kernel AddressSanitizer
(it's kind of chicken and egg problem, you need it to be upstream to
start applying it extensively). To date it has found about 50 bugs.
Bugs that we've found in upstream kernel are listed in [5].
We've also found ~20 bugs in out internal version of the kernel. Also
people from Samsung and Oracle have found some.
[...]
As others noted, the main feature of AddressSanitizer is its
performance due to inline compiler instrumentation and simple linear
shadow memory. User-space Asan has ~2x slowdown on computational
programs and ~2x memory consumption increase. Taking into account that
kernel usually consumes only small fraction of CPU and memory when
running real user-space programs, I would expect that kernel Asan will
have ~10-30% slowdown and similar memory consumption increase (when we
finish all tuning).
I agree that Asan can well replace kmemcheck. We have plans to start
working on Kernel MemorySanitizer that finds uses of unitialized
memory. Asan+Msan will provide feature-parity with kmemcheck. As
others noted, Asan will unlikely replace debug slab and pagealloc that
can be enabled at runtime. Asan uses compiler instrumentation, so even
if it is disabled, it still incurs visible overheads.
Asan technology is easily portable to other architectures. Compiler
instrumentation is fully portable. Runtime has some arch-dependent
parts like shadow mapping and atomic operation interception. They are
relatively easy to port."
Comparison with other debugging features:
========================================
KMEMCHECK:
- KASan can do almost everything that kmemcheck can. KASan uses
compile-time instrumentation, which makes it significantly faster than
kmemcheck. The only advantage of kmemcheck over KASan is detection of
uninitialized memory reads.
Some brief performance testing showed that kasan could be
x500-x600 times faster than kmemcheck:
$ netperf -l 30
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost (127.0.0.1) port 0 AF_INET
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec
no debug: 87380 16384 16384 30.00 41624.72
kasan inline: 87380 16384 16384 30.00 12870.54
kasan outline: 87380 16384 16384 30.00 10586.39
kmemcheck: 87380 16384 16384 30.03 20.23
- Also kmemcheck couldn't work on several CPUs. It always sets
number of CPUs to 1. KASan doesn't have such limitation.
DEBUG_PAGEALLOC:
- KASan is slower than DEBUG_PAGEALLOC, but KASan works on sub-page
granularity level, so it able to find more bugs.
SLUB_DEBUG (poisoning, redzones):
- SLUB_DEBUG has lower overhead than KASan.
- SLUB_DEBUG in most cases are not able to detect bad reads,
KASan able to detect both reads and writes.
- In some cases (e.g. redzone overwritten) SLUB_DEBUG detect
bugs only on allocation/freeing of object. KASan catch
bugs right before it will happen, so we always know exact
place of first bad read/write.
[1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel
[2] https://code.google.com/p/address-sanitizer/wiki/FoundBugs
[3] https://code.google.com/p/thread-sanitizer/wiki/FoundBugs
[4] https://code.google.com/p/memory-sanitizer/wiki/FoundBugs
[5] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel#Trophies
Based on work by Andrey Konovalov.
Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Acked-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrey Konovalov <adech.fo@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Serebryany <kcc@google.com>
Cc: Dmitry Chernenkov <dmitryc@google.com>
Cc: Yuri Gribov <tetra2005@gmail.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-13 22:39:17 +00:00
|
|
|
|
2020-10-13 23:55:02 +00:00
|
|
|
/* kasan_data struct is used in KUnit tests for KASAN expected failures */
|
|
|
|
|
struct kunit_kasan_expectation {
|
|
|
|
|
bool report_expected;
|
|
|
|
|
bool report_found;
|
|
|
|
|
};
|
|
|
|
|
|
2020-12-22 20:00:17 +00:00
|
|
|
#endif
|
|
|
|
|
|
|
|
|
|
#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
|
|
|
|
|
|
|
|
|
|
#include <linux/pgtable.h>
|
|
|
|
|
|
|
|
|
|
/* Software KASAN implementations use shadow memory. */
|
|
|
|
|
|
|
|
|
|
#ifdef CONFIG_KASAN_SW_TAGS
|
|
|
|
|
#define KASAN_SHADOW_INIT 0xFF
|
|
|
|
|
#else
|
|
|
|
|
#define KASAN_SHADOW_INIT 0
|
|
|
|
|
#endif
|
|
|
|
|
|
2018-12-28 08:30:01 +00:00
|
|
|
extern unsigned char kasan_early_shadow_page[PAGE_SIZE];
|
|
|
|
|
extern pte_t kasan_early_shadow_pte[PTRS_PER_PTE];
|
|
|
|
|
extern pmd_t kasan_early_shadow_pmd[PTRS_PER_PMD];
|
|
|
|
|
extern pud_t kasan_early_shadow_pud[PTRS_PER_PUD];
|
|
|
|
|
extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
|
2015-08-13 05:37:24 +00:00
|
|
|
|
2018-12-28 08:30:01 +00:00
|
|
|
int kasan_populate_early_shadow(const void *shadow_start,
|
2015-08-13 05:37:24 +00:00
|
|
|
const void *shadow_end);
|
|
|
|
|
|
kasan: add kernel address sanitizer infrastructure
Kernel Address sanitizer (KASan) is a dynamic memory error detector. It
provides fast and comprehensive solution for finding use-after-free and
out-of-bounds bugs.
KASAN uses compile-time instrumentation for checking every memory access,
therefore GCC > v4.9.2 required. v4.9.2 almost works, but has issues with
putting symbol aliases into the wrong section, which breaks kasan
instrumentation of globals.
This patch only adds infrastructure for kernel address sanitizer. It's
not available for use yet. The idea and some code was borrowed from [1].
Basic idea:
The main idea of KASAN is to use shadow memory to record whether each byte
of memory is safe to access or not, and use compiler's instrumentation to
check the shadow memory on each memory access.
Address sanitizer uses 1/8 of the memory addressable in kernel for shadow
memory and uses direct mapping with a scale and offset to translate a
memory address to its corresponding shadow address.
Here is function to translate address to corresponding shadow address:
unsigned long kasan_mem_to_shadow(unsigned long addr)
{
return (addr >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET;
}
where KASAN_SHADOW_SCALE_SHIFT = 3.
So for every 8 bytes there is one corresponding byte of shadow memory.
The following encoding used for each shadow byte: 0 means that all 8 bytes
of the corresponding memory region are valid for access; k (1 <= k <= 7)
means that the first k bytes are valid for access, and other (8 - k) bytes
are not; Any negative value indicates that the entire 8-bytes are
inaccessible. Different negative values used to distinguish between
different kinds of inaccessible memory (redzones, freed memory) (see
mm/kasan/kasan.h).
To be able to detect accesses to bad memory we need a special compiler.
Such compiler inserts a specific function calls (__asan_load*(addr),
__asan_store*(addr)) before each memory access of size 1, 2, 4, 8 or 16.
These functions check whether memory region is valid to access or not by
checking corresponding shadow memory. If access is not valid an error
printed.
Historical background of the address sanitizer from Dmitry Vyukov:
"We've developed the set of tools, AddressSanitizer (Asan),
ThreadSanitizer and MemorySanitizer, for user space. We actively use
them for testing inside of Google (continuous testing, fuzzing,
running prod services). To date the tools have found more than 10'000
scary bugs in Chromium, Google internal codebase and various
open-source projects (Firefox, OpenSSL, gcc, clang, ffmpeg, MySQL and
lots of others): [2] [3] [4].
The tools are part of both gcc and clang compilers.
We have not yet done massive testing under the Kernel AddressSanitizer
(it's kind of chicken and egg problem, you need it to be upstream to
start applying it extensively). To date it has found about 50 bugs.
Bugs that we've found in upstream kernel are listed in [5].
We've also found ~20 bugs in out internal version of the kernel. Also
people from Samsung and Oracle have found some.
[...]
As others noted, the main feature of AddressSanitizer is its
performance due to inline compiler instrumentation and simple linear
shadow memory. User-space Asan has ~2x slowdown on computational
programs and ~2x memory consumption increase. Taking into account that
kernel usually consumes only small fraction of CPU and memory when
running real user-space programs, I would expect that kernel Asan will
have ~10-30% slowdown and similar memory consumption increase (when we
finish all tuning).
I agree that Asan can well replace kmemcheck. We have plans to start
working on Kernel MemorySanitizer that finds uses of unitialized
memory. Asan+Msan will provide feature-parity with kmemcheck. As
others noted, Asan will unlikely replace debug slab and pagealloc that
can be enabled at runtime. Asan uses compiler instrumentation, so even
if it is disabled, it still incurs visible overheads.
Asan technology is easily portable to other architectures. Compiler
instrumentation is fully portable. Runtime has some arch-dependent
parts like shadow mapping and atomic operation interception. They are
relatively easy to port."
Comparison with other debugging features:
========================================
KMEMCHECK:
- KASan can do almost everything that kmemcheck can. KASan uses
compile-time instrumentation, which makes it significantly faster than
kmemcheck. The only advantage of kmemcheck over KASan is detection of
uninitialized memory reads.
Some brief performance testing showed that kasan could be
x500-x600 times faster than kmemcheck:
$ netperf -l 30
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost (127.0.0.1) port 0 AF_INET
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec
no debug: 87380 16384 16384 30.00 41624.72
kasan inline: 87380 16384 16384 30.00 12870.54
kasan outline: 87380 16384 16384 30.00 10586.39
kmemcheck: 87380 16384 16384 30.03 20.23
- Also kmemcheck couldn't work on several CPUs. It always sets
number of CPUs to 1. KASan doesn't have such limitation.
DEBUG_PAGEALLOC:
- KASan is slower than DEBUG_PAGEALLOC, but KASan works on sub-page
granularity level, so it able to find more bugs.
SLUB_DEBUG (poisoning, redzones):
- SLUB_DEBUG has lower overhead than KASan.
- SLUB_DEBUG in most cases are not able to detect bad reads,
KASan able to detect both reads and writes.
- In some cases (e.g. redzone overwritten) SLUB_DEBUG detect
bugs only on allocation/freeing of object. KASan catch
bugs right before it will happen, so we always know exact
place of first bad read/write.
[1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel
[2] https://code.google.com/p/address-sanitizer/wiki/FoundBugs
[3] https://code.google.com/p/thread-sanitizer/wiki/FoundBugs
[4] https://code.google.com/p/memory-sanitizer/wiki/FoundBugs
[5] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel#Trophies
Based on work by Andrey Konovalov.
Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Acked-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrey Konovalov <adech.fo@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Serebryany <kcc@google.com>
Cc: Dmitry Chernenkov <dmitryc@google.com>
Cc: Yuri Gribov <tetra2005@gmail.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-13 22:39:17 +00:00
|
|
|
static inline void *kasan_mem_to_shadow(const void *addr)
|
|
|
|
|
{
|
|
|
|
|
return (void *)((unsigned long)addr >> KASAN_SHADOW_SCALE_SHIFT)
|
|
|
|
|
+ KASAN_SHADOW_OFFSET;
|
|
|
|
|
}
|
|
|
|
|
|
2020-12-22 20:00:17 +00:00
|
|
|
int kasan_add_zero_shadow(void *start, unsigned long size);
|
|
|
|
|
void kasan_remove_zero_shadow(void *start, unsigned long size);
|
|
|
|
|
|
2020-12-22 20:00:56 +00:00
|
|
|
/* Enable reporting bugs after kasan_disable_current() */
|
|
|
|
|
extern void kasan_enable_current(void);
|
|
|
|
|
|
|
|
|
|
/* Disable reporting bugs for current task */
|
|
|
|
|
extern void kasan_disable_current(void);
|
|
|
|
|
|
2020-12-22 20:00:17 +00:00
|
|
|
#else /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
|
|
|
|
|
|
|
|
|
|
static inline int kasan_add_zero_shadow(void *start, unsigned long size)
|
|
|
|
|
{
|
|
|
|
|
return 0;
|
|
|
|
|
}
|
|
|
|
|
static inline void kasan_remove_zero_shadow(void *start,
|
|
|
|
|
unsigned long size)
|
|
|
|
|
{}
|
|
|
|
|
|
2020-12-22 20:00:56 +00:00
|
|
|
static inline void kasan_enable_current(void) {}
|
|
|
|
|
static inline void kasan_disable_current(void) {}
|
|
|
|
|
|
2020-12-22 20:00:17 +00:00
|
|
|
#endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
|
|
|
|
|
|
|
|
|
|
#ifdef CONFIG_KASAN
|
|
|
|
|
|
2020-12-22 20:03:10 +00:00
|
|
|
struct kasan_cache {
|
|
|
|
|
int alloc_meta_offset;
|
|
|
|
|
int free_meta_offset;
|
|
|
|
|
};
|
kasan: add kernel address sanitizer infrastructure
Kernel Address sanitizer (KASan) is a dynamic memory error detector. It
provides fast and comprehensive solution for finding use-after-free and
out-of-bounds bugs.
KASAN uses compile-time instrumentation for checking every memory access,
therefore GCC > v4.9.2 required. v4.9.2 almost works, but has issues with
putting symbol aliases into the wrong section, which breaks kasan
instrumentation of globals.
This patch only adds infrastructure for kernel address sanitizer. It's
not available for use yet. The idea and some code was borrowed from [1].
Basic idea:
The main idea of KASAN is to use shadow memory to record whether each byte
of memory is safe to access or not, and use compiler's instrumentation to
check the shadow memory on each memory access.
Address sanitizer uses 1/8 of the memory addressable in kernel for shadow
memory and uses direct mapping with a scale and offset to translate a
memory address to its corresponding shadow address.
Here is function to translate address to corresponding shadow address:
unsigned long kasan_mem_to_shadow(unsigned long addr)
{
return (addr >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET;
}
where KASAN_SHADOW_SCALE_SHIFT = 3.
So for every 8 bytes there is one corresponding byte of shadow memory.
The following encoding used for each shadow byte: 0 means that all 8 bytes
of the corresponding memory region are valid for access; k (1 <= k <= 7)
means that the first k bytes are valid for access, and other (8 - k) bytes
are not; Any negative value indicates that the entire 8-bytes are
inaccessible. Different negative values used to distinguish between
different kinds of inaccessible memory (redzones, freed memory) (see
mm/kasan/kasan.h).
To be able to detect accesses to bad memory we need a special compiler.
Such compiler inserts a specific function calls (__asan_load*(addr),
__asan_store*(addr)) before each memory access of size 1, 2, 4, 8 or 16.
These functions check whether memory region is valid to access or not by
checking corresponding shadow memory. If access is not valid an error
printed.
Historical background of the address sanitizer from Dmitry Vyukov:
"We've developed the set of tools, AddressSanitizer (Asan),
ThreadSanitizer and MemorySanitizer, for user space. We actively use
them for testing inside of Google (continuous testing, fuzzing,
running prod services). To date the tools have found more than 10'000
scary bugs in Chromium, Google internal codebase and various
open-source projects (Firefox, OpenSSL, gcc, clang, ffmpeg, MySQL and
lots of others): [2] [3] [4].
The tools are part of both gcc and clang compilers.
We have not yet done massive testing under the Kernel AddressSanitizer
(it's kind of chicken and egg problem, you need it to be upstream to
start applying it extensively). To date it has found about 50 bugs.
Bugs that we've found in upstream kernel are listed in [5].
We've also found ~20 bugs in out internal version of the kernel. Also
people from Samsung and Oracle have found some.
[...]
As others noted, the main feature of AddressSanitizer is its
performance due to inline compiler instrumentation and simple linear
shadow memory. User-space Asan has ~2x slowdown on computational
programs and ~2x memory consumption increase. Taking into account that
kernel usually consumes only small fraction of CPU and memory when
running real user-space programs, I would expect that kernel Asan will
have ~10-30% slowdown and similar memory consumption increase (when we
finish all tuning).
I agree that Asan can well replace kmemcheck. We have plans to start
working on Kernel MemorySanitizer that finds uses of unitialized
memory. Asan+Msan will provide feature-parity with kmemcheck. As
others noted, Asan will unlikely replace debug slab and pagealloc that
can be enabled at runtime. Asan uses compiler instrumentation, so even
if it is disabled, it still incurs visible overheads.
Asan technology is easily portable to other architectures. Compiler
instrumentation is fully portable. Runtime has some arch-dependent
parts like shadow mapping and atomic operation interception. They are
relatively easy to port."
Comparison with other debugging features:
========================================
KMEMCHECK:
- KASan can do almost everything that kmemcheck can. KASan uses
compile-time instrumentation, which makes it significantly faster than
kmemcheck. The only advantage of kmemcheck over KASan is detection of
uninitialized memory reads.
Some brief performance testing showed that kasan could be
x500-x600 times faster than kmemcheck:
$ netperf -l 30
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost (127.0.0.1) port 0 AF_INET
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec
no debug: 87380 16384 16384 30.00 41624.72
kasan inline: 87380 16384 16384 30.00 12870.54
kasan outline: 87380 16384 16384 30.00 10586.39
kmemcheck: 87380 16384 16384 30.03 20.23
- Also kmemcheck couldn't work on several CPUs. It always sets
number of CPUs to 1. KASan doesn't have such limitation.
DEBUG_PAGEALLOC:
- KASan is slower than DEBUG_PAGEALLOC, but KASan works on sub-page
granularity level, so it able to find more bugs.
SLUB_DEBUG (poisoning, redzones):
- SLUB_DEBUG has lower overhead than KASan.
- SLUB_DEBUG in most cases are not able to detect bad reads,
KASan able to detect both reads and writes.
- In some cases (e.g. redzone overwritten) SLUB_DEBUG detect
bugs only on allocation/freeing of object. KASan catch
bugs right before it will happen, so we always know exact
place of first bad read/write.
[1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel
[2] https://code.google.com/p/address-sanitizer/wiki/FoundBugs
[3] https://code.google.com/p/thread-sanitizer/wiki/FoundBugs
[4] https://code.google.com/p/memory-sanitizer/wiki/FoundBugs
[5] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel#Trophies
Based on work by Andrey Konovalov.
Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Acked-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrey Konovalov <adech.fo@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Serebryany <kcc@google.com>
Cc: Dmitry Chernenkov <dmitryc@google.com>
Cc: Yuri Gribov <tetra2005@gmail.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-13 22:39:17 +00:00
|
|
|
|
2020-12-22 20:03:10 +00:00
|
|
|
#ifdef CONFIG_KASAN_HW_TAGS
|
|
|
|
|
DECLARE_STATIC_KEY_FALSE(kasan_flag_enabled);
|
|
|
|
|
static __always_inline bool kasan_enabled(void)
|
|
|
|
|
{
|
|
|
|
|
return static_branch_likely(&kasan_flag_enabled);
|
|
|
|
|
}
|
|
|
|
|
#else
|
|
|
|
|
static inline bool kasan_enabled(void)
|
|
|
|
|
{
|
|
|
|
|
return true;
|
|
|
|
|
}
|
|
|
|
|
#endif
|
2015-02-13 22:39:28 +00:00
|
|
|
|
2020-12-22 20:03:10 +00:00
|
|
|
void __kasan_unpoison_range(const void *addr, size_t size);
|
|
|
|
|
static __always_inline void kasan_unpoison_range(const void *addr, size_t size)
|
|
|
|
|
{
|
|
|
|
|
if (kasan_enabled())
|
|
|
|
|
__kasan_unpoison_range(addr, size);
|
|
|
|
|
}
|
2016-03-25 21:21:59 +00:00
|
|
|
|
2020-12-22 20:03:10 +00:00
|
|
|
void __kasan_alloc_pages(struct page *page, unsigned int order);
|
|
|
|
|
static __always_inline void kasan_alloc_pages(struct page *page,
|
|
|
|
|
unsigned int order)
|
|
|
|
|
{
|
|
|
|
|
if (kasan_enabled())
|
|
|
|
|
__kasan_alloc_pages(page, order);
|
|
|
|
|
}
|
2015-02-13 22:39:42 +00:00
|
|
|
|
2020-12-22 20:03:10 +00:00
|
|
|
void __kasan_free_pages(struct page *page, unsigned int order);
|
|
|
|
|
static __always_inline void kasan_free_pages(struct page *page,
|
|
|
|
|
unsigned int order)
|
|
|
|
|
{
|
|
|
|
|
if (kasan_enabled())
|
|
|
|
|
__kasan_free_pages(page, order);
|
|
|
|
|
}
|
2015-02-13 22:39:42 +00:00
|
|
|
|
2020-12-22 20:03:10 +00:00
|
|
|
void __kasan_cache_create(struct kmem_cache *cache, unsigned int *size,
|
|
|
|
|
slab_flags_t *flags);
|
|
|
|
|
static __always_inline void kasan_cache_create(struct kmem_cache *cache,
|
|
|
|
|
unsigned int *size, slab_flags_t *flags)
|
|
|
|
|
{
|
|
|
|
|
if (kasan_enabled())
|
|
|
|
|
__kasan_cache_create(cache, size, flags);
|
|
|
|
|
}
|
2015-02-13 22:39:42 +00:00
|
|
|
|
2020-12-22 20:03:10 +00:00
|
|
|
size_t __kasan_metadata_size(struct kmem_cache *cache);
|
|
|
|
|
static __always_inline size_t kasan_metadata_size(struct kmem_cache *cache)
|
|
|
|
|
{
|
|
|
|
|
if (kasan_enabled())
|
|
|
|
|
return __kasan_metadata_size(cache);
|
|
|
|
|
return 0;
|
|
|
|
|
}
|
2016-03-25 21:21:59 +00:00
|
|
|
|
2020-12-22 20:03:10 +00:00
|
|
|
void __kasan_poison_slab(struct page *page);
|
|
|
|
|
static __always_inline void kasan_poison_slab(struct page *page)
|
|
|
|
|
{
|
|
|
|
|
if (kasan_enabled())
|
|
|
|
|
__kasan_poison_slab(page);
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
void __kasan_unpoison_object_data(struct kmem_cache *cache, void *object);
|
|
|
|
|
static __always_inline void kasan_unpoison_object_data(struct kmem_cache *cache,
|
|
|
|
|
void *object)
|
|
|
|
|
{
|
|
|
|
|
if (kasan_enabled())
|
|
|
|
|
__kasan_unpoison_object_data(cache, object);
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
void __kasan_poison_object_data(struct kmem_cache *cache, void *object);
|
|
|
|
|
static __always_inline void kasan_poison_object_data(struct kmem_cache *cache,
|
|
|
|
|
void *object)
|
|
|
|
|
{
|
|
|
|
|
if (kasan_enabled())
|
|
|
|
|
__kasan_poison_object_data(cache, object);
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
void * __must_check __kasan_init_slab_obj(struct kmem_cache *cache,
|
|
|
|
|
const void *object);
|
|
|
|
|
static __always_inline void * __must_check kasan_init_slab_obj(
|
|
|
|
|
struct kmem_cache *cache, const void *object)
|
|
|
|
|
{
|
|
|
|
|
if (kasan_enabled())
|
|
|
|
|
return __kasan_init_slab_obj(cache, object);
|
|
|
|
|
return (void *)object;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
bool __kasan_slab_free(struct kmem_cache *s, void *object, unsigned long ip);
|
|
|
|
|
static __always_inline bool kasan_slab_free(struct kmem_cache *s, void *object,
|
|
|
|
|
unsigned long ip)
|
|
|
|
|
{
|
|
|
|
|
if (kasan_enabled())
|
|
|
|
|
return __kasan_slab_free(s, object, ip);
|
|
|
|
|
return false;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
void * __must_check __kasan_slab_alloc(struct kmem_cache *s,
|
|
|
|
|
void *object, gfp_t flags);
|
|
|
|
|
static __always_inline void * __must_check kasan_slab_alloc(
|
|
|
|
|
struct kmem_cache *s, void *object, gfp_t flags)
|
|
|
|
|
{
|
|
|
|
|
if (kasan_enabled())
|
|
|
|
|
return __kasan_slab_alloc(s, object, flags);
|
|
|
|
|
return object;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
void * __must_check __kasan_kmalloc(struct kmem_cache *s, const void *object,
|
|
|
|
|
size_t size, gfp_t flags);
|
|
|
|
|
static __always_inline void * __must_check kasan_kmalloc(struct kmem_cache *s,
|
|
|
|
|
const void *object, size_t size, gfp_t flags)
|
|
|
|
|
{
|
|
|
|
|
if (kasan_enabled())
|
|
|
|
|
return __kasan_kmalloc(s, object, size, flags);
|
|
|
|
|
return (void *)object;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
void * __must_check __kasan_kmalloc_large(const void *ptr,
|
|
|
|
|
size_t size, gfp_t flags);
|
|
|
|
|
static __always_inline void * __must_check kasan_kmalloc_large(const void *ptr,
|
|
|
|
|
size_t size, gfp_t flags)
|
|
|
|
|
{
|
|
|
|
|
if (kasan_enabled())
|
|
|
|
|
return __kasan_kmalloc_large(ptr, size, flags);
|
|
|
|
|
return (void *)ptr;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
void * __must_check __kasan_krealloc(const void *object,
|
|
|
|
|
size_t new_size, gfp_t flags);
|
|
|
|
|
static __always_inline void * __must_check kasan_krealloc(const void *object,
|
|
|
|
|
size_t new_size, gfp_t flags)
|
|
|
|
|
{
|
|
|
|
|
if (kasan_enabled())
|
|
|
|
|
return __kasan_krealloc(object, new_size, flags);
|
|
|
|
|
return (void *)object;
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
void __kasan_poison_kfree(void *ptr, unsigned long ip);
|
|
|
|
|
static __always_inline void kasan_poison_kfree(void *ptr, unsigned long ip)
|
|
|
|
|
{
|
|
|
|
|
if (kasan_enabled())
|
|
|
|
|
__kasan_poison_kfree(ptr, ip);
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
void __kasan_kfree_large(void *ptr, unsigned long ip);
|
|
|
|
|
static __always_inline void kasan_kfree_large(void *ptr, unsigned long ip)
|
|
|
|
|
{
|
|
|
|
|
if (kasan_enabled())
|
|
|
|
|
__kasan_kfree_large(ptr, ip);
|
|
|
|
|
}
|
2016-06-24 21:49:34 +00:00
|
|
|
|
2017-03-31 22:12:04 +00:00
|
|
|
bool kasan_save_enable_multi_shot(void);
|
|
|
|
|
void kasan_restore_multi_shot(bool enabled);
|
|
|
|
|
|
kasan: add kernel address sanitizer infrastructure
Kernel Address sanitizer (KASan) is a dynamic memory error detector. It
provides fast and comprehensive solution for finding use-after-free and
out-of-bounds bugs.
KASAN uses compile-time instrumentation for checking every memory access,
therefore GCC > v4.9.2 required. v4.9.2 almost works, but has issues with
putting symbol aliases into the wrong section, which breaks kasan
instrumentation of globals.
This patch only adds infrastructure for kernel address sanitizer. It's
not available for use yet. The idea and some code was borrowed from [1].
Basic idea:
The main idea of KASAN is to use shadow memory to record whether each byte
of memory is safe to access or not, and use compiler's instrumentation to
check the shadow memory on each memory access.
Address sanitizer uses 1/8 of the memory addressable in kernel for shadow
memory and uses direct mapping with a scale and offset to translate a
memory address to its corresponding shadow address.
Here is function to translate address to corresponding shadow address:
unsigned long kasan_mem_to_shadow(unsigned long addr)
{
return (addr >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET;
}
where KASAN_SHADOW_SCALE_SHIFT = 3.
So for every 8 bytes there is one corresponding byte of shadow memory.
The following encoding used for each shadow byte: 0 means that all 8 bytes
of the corresponding memory region are valid for access; k (1 <= k <= 7)
means that the first k bytes are valid for access, and other (8 - k) bytes
are not; Any negative value indicates that the entire 8-bytes are
inaccessible. Different negative values used to distinguish between
different kinds of inaccessible memory (redzones, freed memory) (see
mm/kasan/kasan.h).
To be able to detect accesses to bad memory we need a special compiler.
Such compiler inserts a specific function calls (__asan_load*(addr),
__asan_store*(addr)) before each memory access of size 1, 2, 4, 8 or 16.
These functions check whether memory region is valid to access or not by
checking corresponding shadow memory. If access is not valid an error
printed.
Historical background of the address sanitizer from Dmitry Vyukov:
"We've developed the set of tools, AddressSanitizer (Asan),
ThreadSanitizer and MemorySanitizer, for user space. We actively use
them for testing inside of Google (continuous testing, fuzzing,
running prod services). To date the tools have found more than 10'000
scary bugs in Chromium, Google internal codebase and various
open-source projects (Firefox, OpenSSL, gcc, clang, ffmpeg, MySQL and
lots of others): [2] [3] [4].
The tools are part of both gcc and clang compilers.
We have not yet done massive testing under the Kernel AddressSanitizer
(it's kind of chicken and egg problem, you need it to be upstream to
start applying it extensively). To date it has found about 50 bugs.
Bugs that we've found in upstream kernel are listed in [5].
We've also found ~20 bugs in out internal version of the kernel. Also
people from Samsung and Oracle have found some.
[...]
As others noted, the main feature of AddressSanitizer is its
performance due to inline compiler instrumentation and simple linear
shadow memory. User-space Asan has ~2x slowdown on computational
programs and ~2x memory consumption increase. Taking into account that
kernel usually consumes only small fraction of CPU and memory when
running real user-space programs, I would expect that kernel Asan will
have ~10-30% slowdown and similar memory consumption increase (when we
finish all tuning).
I agree that Asan can well replace kmemcheck. We have plans to start
working on Kernel MemorySanitizer that finds uses of unitialized
memory. Asan+Msan will provide feature-parity with kmemcheck. As
others noted, Asan will unlikely replace debug slab and pagealloc that
can be enabled at runtime. Asan uses compiler instrumentation, so even
if it is disabled, it still incurs visible overheads.
Asan technology is easily portable to other architectures. Compiler
instrumentation is fully portable. Runtime has some arch-dependent
parts like shadow mapping and atomic operation interception. They are
relatively easy to port."
Comparison with other debugging features:
========================================
KMEMCHECK:
- KASan can do almost everything that kmemcheck can. KASan uses
compile-time instrumentation, which makes it significantly faster than
kmemcheck. The only advantage of kmemcheck over KASan is detection of
uninitialized memory reads.
Some brief performance testing showed that kasan could be
x500-x600 times faster than kmemcheck:
$ netperf -l 30
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost (127.0.0.1) port 0 AF_INET
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec
no debug: 87380 16384 16384 30.00 41624.72
kasan inline: 87380 16384 16384 30.00 12870.54
kasan outline: 87380 16384 16384 30.00 10586.39
kmemcheck: 87380 16384 16384 30.03 20.23
- Also kmemcheck couldn't work on several CPUs. It always sets
number of CPUs to 1. KASan doesn't have such limitation.
DEBUG_PAGEALLOC:
- KASan is slower than DEBUG_PAGEALLOC, but KASan works on sub-page
granularity level, so it able to find more bugs.
SLUB_DEBUG (poisoning, redzones):
- SLUB_DEBUG has lower overhead than KASan.
- SLUB_DEBUG in most cases are not able to detect bad reads,
KASan able to detect both reads and writes.
- In some cases (e.g. redzone overwritten) SLUB_DEBUG detect
bugs only on allocation/freeing of object. KASan catch
bugs right before it will happen, so we always know exact
place of first bad read/write.
[1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel
[2] https://code.google.com/p/address-sanitizer/wiki/FoundBugs
[3] https://code.google.com/p/thread-sanitizer/wiki/FoundBugs
[4] https://code.google.com/p/memory-sanitizer/wiki/FoundBugs
[5] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel#Trophies
Based on work by Andrey Konovalov.
Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Acked-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrey Konovalov <adech.fo@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Serebryany <kcc@google.com>
Cc: Dmitry Chernenkov <dmitryc@google.com>
Cc: Yuri Gribov <tetra2005@gmail.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-13 22:39:17 +00:00
|
|
|
#else /* CONFIG_KASAN */
|
|
|
|
|
|
2020-12-22 20:03:10 +00:00
|
|
|
static inline bool kasan_enabled(void)
|
|
|
|
|
{
|
|
|
|
|
return false;
|
|
|
|
|
}
|
2020-12-22 20:00:21 +00:00
|
|
|
static inline void kasan_unpoison_range(const void *address, size_t size) {}
|
2015-02-13 22:39:28 +00:00
|
|
|
static inline void kasan_alloc_pages(struct page *page, unsigned int order) {}
|
|
|
|
|
static inline void kasan_free_pages(struct page *page, unsigned int order) {}
|
2016-03-25 21:21:59 +00:00
|
|
|
static inline void kasan_cache_create(struct kmem_cache *cache,
|
2018-04-05 23:21:28 +00:00
|
|
|
unsigned int *size,
|
2017-11-16 01:32:18 +00:00
|
|
|
slab_flags_t *flags) {}
|
2020-12-22 20:03:10 +00:00
|
|
|
static inline size_t kasan_metadata_size(struct kmem_cache *cache) { return 0; }
|
2015-02-13 22:39:42 +00:00
|
|
|
static inline void kasan_poison_slab(struct page *page) {}
|
|
|
|
|
static inline void kasan_unpoison_object_data(struct kmem_cache *cache,
|
|
|
|
|
void *object) {}
|
|
|
|
|
static inline void kasan_poison_object_data(struct kmem_cache *cache,
|
|
|
|
|
void *object) {}
|
kasan, mm: change hooks signatures
Patch series "kasan: add software tag-based mode for arm64", v13.
This patchset adds a new software tag-based mode to KASAN [1]. (Initially
this mode was called KHWASAN, but it got renamed, see the naming rationale
at the end of this section).
The plan is to implement HWASan [2] for the kernel with the incentive,
that it's going to have comparable to KASAN performance, but in the same
time consume much less memory, trading that off for somewhat imprecise bug
detection and being supported only for arm64.
The underlying ideas of the approach used by software tag-based KASAN are:
1. By using the Top Byte Ignore (TBI) arm64 CPU feature, we can store
pointer tags in the top byte of each kernel pointer.
2. Using shadow memory, we can store memory tags for each chunk of kernel
memory.
3. On each memory allocation, we can generate a random tag, embed it into
the returned pointer and set the memory tags that correspond to this
chunk of memory to the same value.
4. By using compiler instrumentation, before each memory access we can add
a check that the pointer tag matches the tag of the memory that is being
accessed.
5. On a tag mismatch we report an error.
With this patchset the existing KASAN mode gets renamed to generic KASAN,
with the word "generic" meaning that the implementation can be supported
by any architecture as it is purely software.
The new mode this patchset adds is called software tag-based KASAN. The
word "tag-based" refers to the fact that this mode uses tags embedded into
the top byte of kernel pointers and the TBI arm64 CPU feature that allows
to dereference such pointers. The word "software" here means that shadow
memory manipulation and tag checking on pointer dereference is done in
software. As it is the only tag-based implementation right now, "software
tag-based" KASAN is sometimes referred to as simply "tag-based" in this
patchset.
A potential expansion of this mode is a hardware tag-based mode, which
would use hardware memory tagging support (announced by Arm [3]) instead
of compiler instrumentation and manual shadow memory manipulation.
Same as generic KASAN, software tag-based KASAN is strictly a debugging
feature.
[1] https://www.kernel.org/doc/html/latest/dev-tools/kasan.html
[2] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html
[3] https://community.arm.com/processors/b/blog/posts/arm-a-profile-architecture-2018-developments-armv85a
====== Rationale
On mobile devices generic KASAN's memory usage is significant problem.
One of the main reasons to have tag-based KASAN is to be able to perform a
similar set of checks as the generic one does, but with lower memory
requirements.
Comment from Vishwath Mohan <vishwath@google.com>:
I don't have data on-hand, but anecdotally both ASAN and KASAN have proven
problematic to enable for environments that don't tolerate the increased
memory pressure well. This includes
(a) Low-memory form factors - Wear, TV, Things, lower-tier phones like Go,
(c) Connected components like Pixel's visual core [1].
These are both places I'd love to have a low(er) memory footprint option at
my disposal.
Comment from Evgenii Stepanov <eugenis@google.com>:
Looking at a live Android device under load, slab (according to
/proc/meminfo) + kernel stack take 8-10% available RAM (~350MB). KASAN's
overhead of 2x - 3x on top of it is not insignificant.
Not having this overhead enables near-production use - ex. running
KASAN/KHWASAN kernel on a personal, daily-use device to catch bugs that do
not reproduce in test configuration. These are the ones that often cost
the most engineering time to track down.
CPU overhead is bad, but generally tolerable. RAM is critical, in our
experience. Once it gets low enough, OOM-killer makes your life
miserable.
[1] https://www.blog.google/products/pixel/pixel-visual-core-image-processing-and-machine-learning-pixel-2/
====== Technical details
Software tag-based KASAN mode is implemented in a very similar way to the
generic one. This patchset essentially does the following:
1. TCR_TBI1 is set to enable Top Byte Ignore.
2. Shadow memory is used (with a different scale, 1:16, so each shadow
byte corresponds to 16 bytes of kernel memory) to store memory tags.
3. All slab objects are aligned to shadow scale, which is 16 bytes.
4. All pointers returned from the slab allocator are tagged with a random
tag and the corresponding shadow memory is poisoned with the same value.
5. Compiler instrumentation is used to insert tag checks. Either by
calling callbacks or by inlining them (CONFIG_KASAN_OUTLINE and
CONFIG_KASAN_INLINE flags are reused).
6. When a tag mismatch is detected in callback instrumentation mode
KASAN simply prints a bug report. In case of inline instrumentation,
clang inserts a brk instruction, and KASAN has it's own brk handler,
which reports the bug.
7. The memory in between slab objects is marked with a reserved tag, and
acts as a redzone.
8. When a slab object is freed it's marked with a reserved tag.
Bug detection is imprecise for two reasons:
1. We won't catch some small out-of-bounds accesses, that fall into the
same shadow cell, as the last byte of a slab object.
2. We only have 1 byte to store tags, which means we have a 1/256
probability of a tag match for an incorrect access (actually even
slightly less due to reserved tag values).
Despite that there's a particular type of bugs that tag-based KASAN can
detect compared to generic KASAN: use-after-free after the object has been
allocated by someone else.
====== Testing
Some kernel developers voiced a concern that changing the top byte of
kernel pointers may lead to subtle bugs that are difficult to discover.
To address this concern deliberate testing has been performed.
It doesn't seem feasible to do some kind of static checking to find
potential issues with pointer tagging, so a dynamic approach was taken.
All pointer comparisons/subtractions have been instrumented in an LLVM
compiler pass and a kernel module that would print a bug report whenever
two pointers with different tags are being compared/subtracted (ignoring
comparisons with NULL pointers and with pointers obtained by casting an
error code to a pointer type) has been used. Then the kernel has been
booted in QEMU and on an Odroid C2 board and syzkaller has been run.
This yielded the following results.
The two places that look interesting are:
is_vmalloc_addr in include/linux/mm.h
is_kernel_rodata in mm/util.c
Here we compare a pointer with some fixed untagged values to make sure
that the pointer lies in a particular part of the kernel address space.
Since tag-based KASAN doesn't add tags to pointers that belong to rodata
or vmalloc regions, this should work as is. To make sure debug checks to
those two functions that check that the result doesn't change whether we
operate on pointers with or without untagging has been added.
A few other cases that don't look that interesting:
Comparing pointers to achieve unique sorting order of pointee objects
(e.g. sorting locks addresses before performing a double lock):
tty_ldisc_lock_pair_timeout in drivers/tty/tty_ldisc.c
pipe_double_lock in fs/pipe.c
unix_state_double_lock in net/unix/af_unix.c
lock_two_nondirectories in fs/inode.c
mutex_lock_double in kernel/events/core.c
ep_cmp_ffd in fs/eventpoll.c
fsnotify_compare_groups fs/notify/mark.c
Nothing needs to be done here, since the tags embedded into pointers
don't change, so the sorting order would still be unique.
Checks that a pointer belongs to some particular allocation:
is_sibling_entry in lib/radix-tree.c
object_is_on_stack in include/linux/sched/task_stack.h
Nothing needs to be done here either, since two pointers can only belong
to the same allocation if they have the same tag.
Overall, since the kernel boots and works, there are no critical bugs.
As for the rest, the traditional kernel testing way (use until fails) is
the only one that looks feasible.
Another point here is that tag-based KASAN is available under a separate
config option that needs to be deliberately enabled. Even though it might
be used in a "near-production" environment to find bugs that are not found
during fuzzing or running tests, it is still a debug tool.
====== Benchmarks
The following numbers were collected on Odroid C2 board. Both generic and
tag-based KASAN were used in inline instrumentation mode.
Boot time [1]:
* ~1.7 sec for clean kernel
* ~5.0 sec for generic KASAN
* ~5.0 sec for tag-based KASAN
Network performance [2]:
* 8.33 Gbits/sec for clean kernel
* 3.17 Gbits/sec for generic KASAN
* 2.85 Gbits/sec for tag-based KASAN
Slab memory usage after boot [3]:
* ~40 kb for clean kernel
* ~105 kb (~260% overhead) for generic KASAN
* ~47 kb (~20% overhead) for tag-based KASAN
KASAN memory overhead consists of three main parts:
1. Increased slab memory usage due to redzones.
2. Shadow memory (the whole reserved once during boot).
3. Quaratine (grows gradually until some preset limit; the more the limit,
the more the chance to detect a use-after-free).
Comparing tag-based vs generic KASAN for each of these points:
1. 20% vs 260% overhead.
2. 1/16th vs 1/8th of physical memory.
3. Tag-based KASAN doesn't require quarantine.
[1] Time before the ext4 driver is initialized.
[2] Measured as `iperf -s & iperf -c 127.0.0.1 -t 30`.
[3] Measured as `cat /proc/meminfo | grep Slab`.
====== Some notes
A few notes:
1. The patchset can be found here:
https://github.com/xairy/kasan-prototype/tree/khwasan
2. Building requires a recent Clang version (7.0.0 or later).
3. Stack instrumentation is not supported yet and will be added later.
This patch (of 25):
Tag-based KASAN changes the value of the top byte of pointers returned
from the kernel allocation functions (such as kmalloc). This patch
updates KASAN hooks signatures and their usage in SLAB and SLUB code to
reflect that.
Link: http://lkml.kernel.org/r/aec2b5e3973781ff8a6bb6760f8543643202c451.1544099024.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-12-28 08:29:37 +00:00
|
|
|
static inline void *kasan_init_slab_obj(struct kmem_cache *cache,
|
|
|
|
|
const void *object)
|
|
|
|
|
{
|
|
|
|
|
return (void *)object;
|
|
|
|
|
}
|
2020-12-22 20:03:10 +00:00
|
|
|
static inline bool kasan_slab_free(struct kmem_cache *s, void *object,
|
|
|
|
|
unsigned long ip)
|
|
|
|
|
{
|
|
|
|
|
return false;
|
|
|
|
|
}
|
|
|
|
|
static inline void *kasan_slab_alloc(struct kmem_cache *s, void *object,
|
|
|
|
|
gfp_t flags)
|
kasan, mm: change hooks signatures
Patch series "kasan: add software tag-based mode for arm64", v13.
This patchset adds a new software tag-based mode to KASAN [1]. (Initially
this mode was called KHWASAN, but it got renamed, see the naming rationale
at the end of this section).
The plan is to implement HWASan [2] for the kernel with the incentive,
that it's going to have comparable to KASAN performance, but in the same
time consume much less memory, trading that off for somewhat imprecise bug
detection and being supported only for arm64.
The underlying ideas of the approach used by software tag-based KASAN are:
1. By using the Top Byte Ignore (TBI) arm64 CPU feature, we can store
pointer tags in the top byte of each kernel pointer.
2. Using shadow memory, we can store memory tags for each chunk of kernel
memory.
3. On each memory allocation, we can generate a random tag, embed it into
the returned pointer and set the memory tags that correspond to this
chunk of memory to the same value.
4. By using compiler instrumentation, before each memory access we can add
a check that the pointer tag matches the tag of the memory that is being
accessed.
5. On a tag mismatch we report an error.
With this patchset the existing KASAN mode gets renamed to generic KASAN,
with the word "generic" meaning that the implementation can be supported
by any architecture as it is purely software.
The new mode this patchset adds is called software tag-based KASAN. The
word "tag-based" refers to the fact that this mode uses tags embedded into
the top byte of kernel pointers and the TBI arm64 CPU feature that allows
to dereference such pointers. The word "software" here means that shadow
memory manipulation and tag checking on pointer dereference is done in
software. As it is the only tag-based implementation right now, "software
tag-based" KASAN is sometimes referred to as simply "tag-based" in this
patchset.
A potential expansion of this mode is a hardware tag-based mode, which
would use hardware memory tagging support (announced by Arm [3]) instead
of compiler instrumentation and manual shadow memory manipulation.
Same as generic KASAN, software tag-based KASAN is strictly a debugging
feature.
[1] https://www.kernel.org/doc/html/latest/dev-tools/kasan.html
[2] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html
[3] https://community.arm.com/processors/b/blog/posts/arm-a-profile-architecture-2018-developments-armv85a
====== Rationale
On mobile devices generic KASAN's memory usage is significant problem.
One of the main reasons to have tag-based KASAN is to be able to perform a
similar set of checks as the generic one does, but with lower memory
requirements.
Comment from Vishwath Mohan <vishwath@google.com>:
I don't have data on-hand, but anecdotally both ASAN and KASAN have proven
problematic to enable for environments that don't tolerate the increased
memory pressure well. This includes
(a) Low-memory form factors - Wear, TV, Things, lower-tier phones like Go,
(c) Connected components like Pixel's visual core [1].
These are both places I'd love to have a low(er) memory footprint option at
my disposal.
Comment from Evgenii Stepanov <eugenis@google.com>:
Looking at a live Android device under load, slab (according to
/proc/meminfo) + kernel stack take 8-10% available RAM (~350MB). KASAN's
overhead of 2x - 3x on top of it is not insignificant.
Not having this overhead enables near-production use - ex. running
KASAN/KHWASAN kernel on a personal, daily-use device to catch bugs that do
not reproduce in test configuration. These are the ones that often cost
the most engineering time to track down.
CPU overhead is bad, but generally tolerable. RAM is critical, in our
experience. Once it gets low enough, OOM-killer makes your life
miserable.
[1] https://www.blog.google/products/pixel/pixel-visual-core-image-processing-and-machine-learning-pixel-2/
====== Technical details
Software tag-based KASAN mode is implemented in a very similar way to the
generic one. This patchset essentially does the following:
1. TCR_TBI1 is set to enable Top Byte Ignore.
2. Shadow memory is used (with a different scale, 1:16, so each shadow
byte corresponds to 16 bytes of kernel memory) to store memory tags.
3. All slab objects are aligned to shadow scale, which is 16 bytes.
4. All pointers returned from the slab allocator are tagged with a random
tag and the corresponding shadow memory is poisoned with the same value.
5. Compiler instrumentation is used to insert tag checks. Either by
calling callbacks or by inlining them (CONFIG_KASAN_OUTLINE and
CONFIG_KASAN_INLINE flags are reused).
6. When a tag mismatch is detected in callback instrumentation mode
KASAN simply prints a bug report. In case of inline instrumentation,
clang inserts a brk instruction, and KASAN has it's own brk handler,
which reports the bug.
7. The memory in between slab objects is marked with a reserved tag, and
acts as a redzone.
8. When a slab object is freed it's marked with a reserved tag.
Bug detection is imprecise for two reasons:
1. We won't catch some small out-of-bounds accesses, that fall into the
same shadow cell, as the last byte of a slab object.
2. We only have 1 byte to store tags, which means we have a 1/256
probability of a tag match for an incorrect access (actually even
slightly less due to reserved tag values).
Despite that there's a particular type of bugs that tag-based KASAN can
detect compared to generic KASAN: use-after-free after the object has been
allocated by someone else.
====== Testing
Some kernel developers voiced a concern that changing the top byte of
kernel pointers may lead to subtle bugs that are difficult to discover.
To address this concern deliberate testing has been performed.
It doesn't seem feasible to do some kind of static checking to find
potential issues with pointer tagging, so a dynamic approach was taken.
All pointer comparisons/subtractions have been instrumented in an LLVM
compiler pass and a kernel module that would print a bug report whenever
two pointers with different tags are being compared/subtracted (ignoring
comparisons with NULL pointers and with pointers obtained by casting an
error code to a pointer type) has been used. Then the kernel has been
booted in QEMU and on an Odroid C2 board and syzkaller has been run.
This yielded the following results.
The two places that look interesting are:
is_vmalloc_addr in include/linux/mm.h
is_kernel_rodata in mm/util.c
Here we compare a pointer with some fixed untagged values to make sure
that the pointer lies in a particular part of the kernel address space.
Since tag-based KASAN doesn't add tags to pointers that belong to rodata
or vmalloc regions, this should work as is. To make sure debug checks to
those two functions that check that the result doesn't change whether we
operate on pointers with or without untagging has been added.
A few other cases that don't look that interesting:
Comparing pointers to achieve unique sorting order of pointee objects
(e.g. sorting locks addresses before performing a double lock):
tty_ldisc_lock_pair_timeout in drivers/tty/tty_ldisc.c
pipe_double_lock in fs/pipe.c
unix_state_double_lock in net/unix/af_unix.c
lock_two_nondirectories in fs/inode.c
mutex_lock_double in kernel/events/core.c
ep_cmp_ffd in fs/eventpoll.c
fsnotify_compare_groups fs/notify/mark.c
Nothing needs to be done here, since the tags embedded into pointers
don't change, so the sorting order would still be unique.
Checks that a pointer belongs to some particular allocation:
is_sibling_entry in lib/radix-tree.c
object_is_on_stack in include/linux/sched/task_stack.h
Nothing needs to be done here either, since two pointers can only belong
to the same allocation if they have the same tag.
Overall, since the kernel boots and works, there are no critical bugs.
As for the rest, the traditional kernel testing way (use until fails) is
the only one that looks feasible.
Another point here is that tag-based KASAN is available under a separate
config option that needs to be deliberately enabled. Even though it might
be used in a "near-production" environment to find bugs that are not found
during fuzzing or running tests, it is still a debug tool.
====== Benchmarks
The following numbers were collected on Odroid C2 board. Both generic and
tag-based KASAN were used in inline instrumentation mode.
Boot time [1]:
* ~1.7 sec for clean kernel
* ~5.0 sec for generic KASAN
* ~5.0 sec for tag-based KASAN
Network performance [2]:
* 8.33 Gbits/sec for clean kernel
* 3.17 Gbits/sec for generic KASAN
* 2.85 Gbits/sec for tag-based KASAN
Slab memory usage after boot [3]:
* ~40 kb for clean kernel
* ~105 kb (~260% overhead) for generic KASAN
* ~47 kb (~20% overhead) for tag-based KASAN
KASAN memory overhead consists of three main parts:
1. Increased slab memory usage due to redzones.
2. Shadow memory (the whole reserved once during boot).
3. Quaratine (grows gradually until some preset limit; the more the limit,
the more the chance to detect a use-after-free).
Comparing tag-based vs generic KASAN for each of these points:
1. 20% vs 260% overhead.
2. 1/16th vs 1/8th of physical memory.
3. Tag-based KASAN doesn't require quarantine.
[1] Time before the ext4 driver is initialized.
[2] Measured as `iperf -s & iperf -c 127.0.0.1 -t 30`.
[3] Measured as `cat /proc/meminfo | grep Slab`.
====== Some notes
A few notes:
1. The patchset can be found here:
https://github.com/xairy/kasan-prototype/tree/khwasan
2. Building requires a recent Clang version (7.0.0 or later).
3. Stack instrumentation is not supported yet and will be added later.
This patch (of 25):
Tag-based KASAN changes the value of the top byte of pointers returned
from the kernel allocation functions (such as kmalloc). This patch
updates KASAN hooks signatures and their usage in SLAB and SLUB code to
reflect that.
Link: http://lkml.kernel.org/r/aec2b5e3973781ff8a6bb6760f8543643202c451.1544099024.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-12-28 08:29:37 +00:00
|
|
|
{
|
2020-12-22 20:03:10 +00:00
|
|
|
return object;
|
kasan, mm: change hooks signatures
Patch series "kasan: add software tag-based mode for arm64", v13.
This patchset adds a new software tag-based mode to KASAN [1]. (Initially
this mode was called KHWASAN, but it got renamed, see the naming rationale
at the end of this section).
The plan is to implement HWASan [2] for the kernel with the incentive,
that it's going to have comparable to KASAN performance, but in the same
time consume much less memory, trading that off for somewhat imprecise bug
detection and being supported only for arm64.
The underlying ideas of the approach used by software tag-based KASAN are:
1. By using the Top Byte Ignore (TBI) arm64 CPU feature, we can store
pointer tags in the top byte of each kernel pointer.
2. Using shadow memory, we can store memory tags for each chunk of kernel
memory.
3. On each memory allocation, we can generate a random tag, embed it into
the returned pointer and set the memory tags that correspond to this
chunk of memory to the same value.
4. By using compiler instrumentation, before each memory access we can add
a check that the pointer tag matches the tag of the memory that is being
accessed.
5. On a tag mismatch we report an error.
With this patchset the existing KASAN mode gets renamed to generic KASAN,
with the word "generic" meaning that the implementation can be supported
by any architecture as it is purely software.
The new mode this patchset adds is called software tag-based KASAN. The
word "tag-based" refers to the fact that this mode uses tags embedded into
the top byte of kernel pointers and the TBI arm64 CPU feature that allows
to dereference such pointers. The word "software" here means that shadow
memory manipulation and tag checking on pointer dereference is done in
software. As it is the only tag-based implementation right now, "software
tag-based" KASAN is sometimes referred to as simply "tag-based" in this
patchset.
A potential expansion of this mode is a hardware tag-based mode, which
would use hardware memory tagging support (announced by Arm [3]) instead
of compiler instrumentation and manual shadow memory manipulation.
Same as generic KASAN, software tag-based KASAN is strictly a debugging
feature.
[1] https://www.kernel.org/doc/html/latest/dev-tools/kasan.html
[2] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html
[3] https://community.arm.com/processors/b/blog/posts/arm-a-profile-architecture-2018-developments-armv85a
====== Rationale
On mobile devices generic KASAN's memory usage is significant problem.
One of the main reasons to have tag-based KASAN is to be able to perform a
similar set of checks as the generic one does, but with lower memory
requirements.
Comment from Vishwath Mohan <vishwath@google.com>:
I don't have data on-hand, but anecdotally both ASAN and KASAN have proven
problematic to enable for environments that don't tolerate the increased
memory pressure well. This includes
(a) Low-memory form factors - Wear, TV, Things, lower-tier phones like Go,
(c) Connected components like Pixel's visual core [1].
These are both places I'd love to have a low(er) memory footprint option at
my disposal.
Comment from Evgenii Stepanov <eugenis@google.com>:
Looking at a live Android device under load, slab (according to
/proc/meminfo) + kernel stack take 8-10% available RAM (~350MB). KASAN's
overhead of 2x - 3x on top of it is not insignificant.
Not having this overhead enables near-production use - ex. running
KASAN/KHWASAN kernel on a personal, daily-use device to catch bugs that do
not reproduce in test configuration. These are the ones that often cost
the most engineering time to track down.
CPU overhead is bad, but generally tolerable. RAM is critical, in our
experience. Once it gets low enough, OOM-killer makes your life
miserable.
[1] https://www.blog.google/products/pixel/pixel-visual-core-image-processing-and-machine-learning-pixel-2/
====== Technical details
Software tag-based KASAN mode is implemented in a very similar way to the
generic one. This patchset essentially does the following:
1. TCR_TBI1 is set to enable Top Byte Ignore.
2. Shadow memory is used (with a different scale, 1:16, so each shadow
byte corresponds to 16 bytes of kernel memory) to store memory tags.
3. All slab objects are aligned to shadow scale, which is 16 bytes.
4. All pointers returned from the slab allocator are tagged with a random
tag and the corresponding shadow memory is poisoned with the same value.
5. Compiler instrumentation is used to insert tag checks. Either by
calling callbacks or by inlining them (CONFIG_KASAN_OUTLINE and
CONFIG_KASAN_INLINE flags are reused).
6. When a tag mismatch is detected in callback instrumentation mode
KASAN simply prints a bug report. In case of inline instrumentation,
clang inserts a brk instruction, and KASAN has it's own brk handler,
which reports the bug.
7. The memory in between slab objects is marked with a reserved tag, and
acts as a redzone.
8. When a slab object is freed it's marked with a reserved tag.
Bug detection is imprecise for two reasons:
1. We won't catch some small out-of-bounds accesses, that fall into the
same shadow cell, as the last byte of a slab object.
2. We only have 1 byte to store tags, which means we have a 1/256
probability of a tag match for an incorrect access (actually even
slightly less due to reserved tag values).
Despite that there's a particular type of bugs that tag-based KASAN can
detect compared to generic KASAN: use-after-free after the object has been
allocated by someone else.
====== Testing
Some kernel developers voiced a concern that changing the top byte of
kernel pointers may lead to subtle bugs that are difficult to discover.
To address this concern deliberate testing has been performed.
It doesn't seem feasible to do some kind of static checking to find
potential issues with pointer tagging, so a dynamic approach was taken.
All pointer comparisons/subtractions have been instrumented in an LLVM
compiler pass and a kernel module that would print a bug report whenever
two pointers with different tags are being compared/subtracted (ignoring
comparisons with NULL pointers and with pointers obtained by casting an
error code to a pointer type) has been used. Then the kernel has been
booted in QEMU and on an Odroid C2 board and syzkaller has been run.
This yielded the following results.
The two places that look interesting are:
is_vmalloc_addr in include/linux/mm.h
is_kernel_rodata in mm/util.c
Here we compare a pointer with some fixed untagged values to make sure
that the pointer lies in a particular part of the kernel address space.
Since tag-based KASAN doesn't add tags to pointers that belong to rodata
or vmalloc regions, this should work as is. To make sure debug checks to
those two functions that check that the result doesn't change whether we
operate on pointers with or without untagging has been added.
A few other cases that don't look that interesting:
Comparing pointers to achieve unique sorting order of pointee objects
(e.g. sorting locks addresses before performing a double lock):
tty_ldisc_lock_pair_timeout in drivers/tty/tty_ldisc.c
pipe_double_lock in fs/pipe.c
unix_state_double_lock in net/unix/af_unix.c
lock_two_nondirectories in fs/inode.c
mutex_lock_double in kernel/events/core.c
ep_cmp_ffd in fs/eventpoll.c
fsnotify_compare_groups fs/notify/mark.c
Nothing needs to be done here, since the tags embedded into pointers
don't change, so the sorting order would still be unique.
Checks that a pointer belongs to some particular allocation:
is_sibling_entry in lib/radix-tree.c
object_is_on_stack in include/linux/sched/task_stack.h
Nothing needs to be done here either, since two pointers can only belong
to the same allocation if they have the same tag.
Overall, since the kernel boots and works, there are no critical bugs.
As for the rest, the traditional kernel testing way (use until fails) is
the only one that looks feasible.
Another point here is that tag-based KASAN is available under a separate
config option that needs to be deliberately enabled. Even though it might
be used in a "near-production" environment to find bugs that are not found
during fuzzing or running tests, it is still a debug tool.
====== Benchmarks
The following numbers were collected on Odroid C2 board. Both generic and
tag-based KASAN were used in inline instrumentation mode.
Boot time [1]:
* ~1.7 sec for clean kernel
* ~5.0 sec for generic KASAN
* ~5.0 sec for tag-based KASAN
Network performance [2]:
* 8.33 Gbits/sec for clean kernel
* 3.17 Gbits/sec for generic KASAN
* 2.85 Gbits/sec for tag-based KASAN
Slab memory usage after boot [3]:
* ~40 kb for clean kernel
* ~105 kb (~260% overhead) for generic KASAN
* ~47 kb (~20% overhead) for tag-based KASAN
KASAN memory overhead consists of three main parts:
1. Increased slab memory usage due to redzones.
2. Shadow memory (the whole reserved once during boot).
3. Quaratine (grows gradually until some preset limit; the more the limit,
the more the chance to detect a use-after-free).
Comparing tag-based vs generic KASAN for each of these points:
1. 20% vs 260% overhead.
2. 1/16th vs 1/8th of physical memory.
3. Tag-based KASAN doesn't require quarantine.
[1] Time before the ext4 driver is initialized.
[2] Measured as `iperf -s & iperf -c 127.0.0.1 -t 30`.
[3] Measured as `cat /proc/meminfo | grep Slab`.
====== Some notes
A few notes:
1. The patchset can be found here:
https://github.com/xairy/kasan-prototype/tree/khwasan
2. Building requires a recent Clang version (7.0.0 or later).
3. Stack instrumentation is not supported yet and will be added later.
This patch (of 25):
Tag-based KASAN changes the value of the top byte of pointers returned
from the kernel allocation functions (such as kmalloc). This patch
updates KASAN hooks signatures and their usage in SLAB and SLUB code to
reflect that.
Link: http://lkml.kernel.org/r/aec2b5e3973781ff8a6bb6760f8543643202c451.1544099024.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-12-28 08:29:37 +00:00
|
|
|
}
|
|
|
|
|
static inline void *kasan_kmalloc(struct kmem_cache *s, const void *object,
|
|
|
|
|
size_t size, gfp_t flags)
|
|
|
|
|
{
|
|
|
|
|
return (void *)object;
|
|
|
|
|
}
|
2020-12-22 20:03:10 +00:00
|
|
|
static inline void *kasan_kmalloc_large(const void *ptr, size_t size, gfp_t flags)
|
|
|
|
|
{
|
|
|
|
|
return (void *)ptr;
|
|
|
|
|
}
|
kasan, mm: change hooks signatures
Patch series "kasan: add software tag-based mode for arm64", v13.
This patchset adds a new software tag-based mode to KASAN [1]. (Initially
this mode was called KHWASAN, but it got renamed, see the naming rationale
at the end of this section).
The plan is to implement HWASan [2] for the kernel with the incentive,
that it's going to have comparable to KASAN performance, but in the same
time consume much less memory, trading that off for somewhat imprecise bug
detection and being supported only for arm64.
The underlying ideas of the approach used by software tag-based KASAN are:
1. By using the Top Byte Ignore (TBI) arm64 CPU feature, we can store
pointer tags in the top byte of each kernel pointer.
2. Using shadow memory, we can store memory tags for each chunk of kernel
memory.
3. On each memory allocation, we can generate a random tag, embed it into
the returned pointer and set the memory tags that correspond to this
chunk of memory to the same value.
4. By using compiler instrumentation, before each memory access we can add
a check that the pointer tag matches the tag of the memory that is being
accessed.
5. On a tag mismatch we report an error.
With this patchset the existing KASAN mode gets renamed to generic KASAN,
with the word "generic" meaning that the implementation can be supported
by any architecture as it is purely software.
The new mode this patchset adds is called software tag-based KASAN. The
word "tag-based" refers to the fact that this mode uses tags embedded into
the top byte of kernel pointers and the TBI arm64 CPU feature that allows
to dereference such pointers. The word "software" here means that shadow
memory manipulation and tag checking on pointer dereference is done in
software. As it is the only tag-based implementation right now, "software
tag-based" KASAN is sometimes referred to as simply "tag-based" in this
patchset.
A potential expansion of this mode is a hardware tag-based mode, which
would use hardware memory tagging support (announced by Arm [3]) instead
of compiler instrumentation and manual shadow memory manipulation.
Same as generic KASAN, software tag-based KASAN is strictly a debugging
feature.
[1] https://www.kernel.org/doc/html/latest/dev-tools/kasan.html
[2] http://clang.llvm.org/docs/HardwareAssistedAddressSanitizerDesign.html
[3] https://community.arm.com/processors/b/blog/posts/arm-a-profile-architecture-2018-developments-armv85a
====== Rationale
On mobile devices generic KASAN's memory usage is significant problem.
One of the main reasons to have tag-based KASAN is to be able to perform a
similar set of checks as the generic one does, but with lower memory
requirements.
Comment from Vishwath Mohan <vishwath@google.com>:
I don't have data on-hand, but anecdotally both ASAN and KASAN have proven
problematic to enable for environments that don't tolerate the increased
memory pressure well. This includes
(a) Low-memory form factors - Wear, TV, Things, lower-tier phones like Go,
(c) Connected components like Pixel's visual core [1].
These are both places I'd love to have a low(er) memory footprint option at
my disposal.
Comment from Evgenii Stepanov <eugenis@google.com>:
Looking at a live Android device under load, slab (according to
/proc/meminfo) + kernel stack take 8-10% available RAM (~350MB). KASAN's
overhead of 2x - 3x on top of it is not insignificant.
Not having this overhead enables near-production use - ex. running
KASAN/KHWASAN kernel on a personal, daily-use device to catch bugs that do
not reproduce in test configuration. These are the ones that often cost
the most engineering time to track down.
CPU overhead is bad, but generally tolerable. RAM is critical, in our
experience. Once it gets low enough, OOM-killer makes your life
miserable.
[1] https://www.blog.google/products/pixel/pixel-visual-core-image-processing-and-machine-learning-pixel-2/
====== Technical details
Software tag-based KASAN mode is implemented in a very similar way to the
generic one. This patchset essentially does the following:
1. TCR_TBI1 is set to enable Top Byte Ignore.
2. Shadow memory is used (with a different scale, 1:16, so each shadow
byte corresponds to 16 bytes of kernel memory) to store memory tags.
3. All slab objects are aligned to shadow scale, which is 16 bytes.
4. All pointers returned from the slab allocator are tagged with a random
tag and the corresponding shadow memory is poisoned with the same value.
5. Compiler instrumentation is used to insert tag checks. Either by
calling callbacks or by inlining them (CONFIG_KASAN_OUTLINE and
CONFIG_KASAN_INLINE flags are reused).
6. When a tag mismatch is detected in callback instrumentation mode
KASAN simply prints a bug report. In case of inline instrumentation,
clang inserts a brk instruction, and KASAN has it's own brk handler,
which reports the bug.
7. The memory in between slab objects is marked with a reserved tag, and
acts as a redzone.
8. When a slab object is freed it's marked with a reserved tag.
Bug detection is imprecise for two reasons:
1. We won't catch some small out-of-bounds accesses, that fall into the
same shadow cell, as the last byte of a slab object.
2. We only have 1 byte to store tags, which means we have a 1/256
probability of a tag match for an incorrect access (actually even
slightly less due to reserved tag values).
Despite that there's a particular type of bugs that tag-based KASAN can
detect compared to generic KASAN: use-after-free after the object has been
allocated by someone else.
====== Testing
Some kernel developers voiced a concern that changing the top byte of
kernel pointers may lead to subtle bugs that are difficult to discover.
To address this concern deliberate testing has been performed.
It doesn't seem feasible to do some kind of static checking to find
potential issues with pointer tagging, so a dynamic approach was taken.
All pointer comparisons/subtractions have been instrumented in an LLVM
compiler pass and a kernel module that would print a bug report whenever
two pointers with different tags are being compared/subtracted (ignoring
comparisons with NULL pointers and with pointers obtained by casting an
error code to a pointer type) has been used. Then the kernel has been
booted in QEMU and on an Odroid C2 board and syzkaller has been run.
This yielded the following results.
The two places that look interesting are:
is_vmalloc_addr in include/linux/mm.h
is_kernel_rodata in mm/util.c
Here we compare a pointer with some fixed untagged values to make sure
that the pointer lies in a particular part of the kernel address space.
Since tag-based KASAN doesn't add tags to pointers that belong to rodata
or vmalloc regions, this should work as is. To make sure debug checks to
those two functions that check that the result doesn't change whether we
operate on pointers with or without untagging has been added.
A few other cases that don't look that interesting:
Comparing pointers to achieve unique sorting order of pointee objects
(e.g. sorting locks addresses before performing a double lock):
tty_ldisc_lock_pair_timeout in drivers/tty/tty_ldisc.c
pipe_double_lock in fs/pipe.c
unix_state_double_lock in net/unix/af_unix.c
lock_two_nondirectories in fs/inode.c
mutex_lock_double in kernel/events/core.c
ep_cmp_ffd in fs/eventpoll.c
fsnotify_compare_groups fs/notify/mark.c
Nothing needs to be done here, since the tags embedded into pointers
don't change, so the sorting order would still be unique.
Checks that a pointer belongs to some particular allocation:
is_sibling_entry in lib/radix-tree.c
object_is_on_stack in include/linux/sched/task_stack.h
Nothing needs to be done here either, since two pointers can only belong
to the same allocation if they have the same tag.
Overall, since the kernel boots and works, there are no critical bugs.
As for the rest, the traditional kernel testing way (use until fails) is
the only one that looks feasible.
Another point here is that tag-based KASAN is available under a separate
config option that needs to be deliberately enabled. Even though it might
be used in a "near-production" environment to find bugs that are not found
during fuzzing or running tests, it is still a debug tool.
====== Benchmarks
The following numbers were collected on Odroid C2 board. Both generic and
tag-based KASAN were used in inline instrumentation mode.
Boot time [1]:
* ~1.7 sec for clean kernel
* ~5.0 sec for generic KASAN
* ~5.0 sec for tag-based KASAN
Network performance [2]:
* 8.33 Gbits/sec for clean kernel
* 3.17 Gbits/sec for generic KASAN
* 2.85 Gbits/sec for tag-based KASAN
Slab memory usage after boot [3]:
* ~40 kb for clean kernel
* ~105 kb (~260% overhead) for generic KASAN
* ~47 kb (~20% overhead) for tag-based KASAN
KASAN memory overhead consists of three main parts:
1. Increased slab memory usage due to redzones.
2. Shadow memory (the whole reserved once during boot).
3. Quaratine (grows gradually until some preset limit; the more the limit,
the more the chance to detect a use-after-free).
Comparing tag-based vs generic KASAN for each of these points:
1. 20% vs 260% overhead.
2. 1/16th vs 1/8th of physical memory.
3. Tag-based KASAN doesn't require quarantine.
[1] Time before the ext4 driver is initialized.
[2] Measured as `iperf -s & iperf -c 127.0.0.1 -t 30`.
[3] Measured as `cat /proc/meminfo | grep Slab`.
====== Some notes
A few notes:
1. The patchset can be found here:
https://github.com/xairy/kasan-prototype/tree/khwasan
2. Building requires a recent Clang version (7.0.0 or later).
3. Stack instrumentation is not supported yet and will be added later.
This patch (of 25):
Tag-based KASAN changes the value of the top byte of pointers returned
from the kernel allocation functions (such as kmalloc). This patch
updates KASAN hooks signatures and their usage in SLAB and SLUB code to
reflect that.
Link: http://lkml.kernel.org/r/aec2b5e3973781ff8a6bb6760f8543643202c451.1544099024.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2018-12-28 08:29:37 +00:00
|
|
|
static inline void *kasan_krealloc(const void *object, size_t new_size,
|
|
|
|
|
gfp_t flags)
|
|
|
|
|
{
|
|
|
|
|
return (void *)object;
|
|
|
|
|
}
|
2020-12-22 20:03:10 +00:00
|
|
|
static inline void kasan_poison_kfree(void *ptr, unsigned long ip) {}
|
|
|
|
|
static inline void kasan_kfree_large(void *ptr, unsigned long ip) {}
|
2016-06-24 21:49:34 +00:00
|
|
|
|
kasan: add kernel address sanitizer infrastructure
Kernel Address sanitizer (KASan) is a dynamic memory error detector. It
provides fast and comprehensive solution for finding use-after-free and
out-of-bounds bugs.
KASAN uses compile-time instrumentation for checking every memory access,
therefore GCC > v4.9.2 required. v4.9.2 almost works, but has issues with
putting symbol aliases into the wrong section, which breaks kasan
instrumentation of globals.
This patch only adds infrastructure for kernel address sanitizer. It's
not available for use yet. The idea and some code was borrowed from [1].
Basic idea:
The main idea of KASAN is to use shadow memory to record whether each byte
of memory is safe to access or not, and use compiler's instrumentation to
check the shadow memory on each memory access.
Address sanitizer uses 1/8 of the memory addressable in kernel for shadow
memory and uses direct mapping with a scale and offset to translate a
memory address to its corresponding shadow address.
Here is function to translate address to corresponding shadow address:
unsigned long kasan_mem_to_shadow(unsigned long addr)
{
return (addr >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET;
}
where KASAN_SHADOW_SCALE_SHIFT = 3.
So for every 8 bytes there is one corresponding byte of shadow memory.
The following encoding used for each shadow byte: 0 means that all 8 bytes
of the corresponding memory region are valid for access; k (1 <= k <= 7)
means that the first k bytes are valid for access, and other (8 - k) bytes
are not; Any negative value indicates that the entire 8-bytes are
inaccessible. Different negative values used to distinguish between
different kinds of inaccessible memory (redzones, freed memory) (see
mm/kasan/kasan.h).
To be able to detect accesses to bad memory we need a special compiler.
Such compiler inserts a specific function calls (__asan_load*(addr),
__asan_store*(addr)) before each memory access of size 1, 2, 4, 8 or 16.
These functions check whether memory region is valid to access or not by
checking corresponding shadow memory. If access is not valid an error
printed.
Historical background of the address sanitizer from Dmitry Vyukov:
"We've developed the set of tools, AddressSanitizer (Asan),
ThreadSanitizer and MemorySanitizer, for user space. We actively use
them for testing inside of Google (continuous testing, fuzzing,
running prod services). To date the tools have found more than 10'000
scary bugs in Chromium, Google internal codebase and various
open-source projects (Firefox, OpenSSL, gcc, clang, ffmpeg, MySQL and
lots of others): [2] [3] [4].
The tools are part of both gcc and clang compilers.
We have not yet done massive testing under the Kernel AddressSanitizer
(it's kind of chicken and egg problem, you need it to be upstream to
start applying it extensively). To date it has found about 50 bugs.
Bugs that we've found in upstream kernel are listed in [5].
We've also found ~20 bugs in out internal version of the kernel. Also
people from Samsung and Oracle have found some.
[...]
As others noted, the main feature of AddressSanitizer is its
performance due to inline compiler instrumentation and simple linear
shadow memory. User-space Asan has ~2x slowdown on computational
programs and ~2x memory consumption increase. Taking into account that
kernel usually consumes only small fraction of CPU and memory when
running real user-space programs, I would expect that kernel Asan will
have ~10-30% slowdown and similar memory consumption increase (when we
finish all tuning).
I agree that Asan can well replace kmemcheck. We have plans to start
working on Kernel MemorySanitizer that finds uses of unitialized
memory. Asan+Msan will provide feature-parity with kmemcheck. As
others noted, Asan will unlikely replace debug slab and pagealloc that
can be enabled at runtime. Asan uses compiler instrumentation, so even
if it is disabled, it still incurs visible overheads.
Asan technology is easily portable to other architectures. Compiler
instrumentation is fully portable. Runtime has some arch-dependent
parts like shadow mapping and atomic operation interception. They are
relatively easy to port."
Comparison with other debugging features:
========================================
KMEMCHECK:
- KASan can do almost everything that kmemcheck can. KASan uses
compile-time instrumentation, which makes it significantly faster than
kmemcheck. The only advantage of kmemcheck over KASan is detection of
uninitialized memory reads.
Some brief performance testing showed that kasan could be
x500-x600 times faster than kmemcheck:
$ netperf -l 30
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost (127.0.0.1) port 0 AF_INET
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec
no debug: 87380 16384 16384 30.00 41624.72
kasan inline: 87380 16384 16384 30.00 12870.54
kasan outline: 87380 16384 16384 30.00 10586.39
kmemcheck: 87380 16384 16384 30.03 20.23
- Also kmemcheck couldn't work on several CPUs. It always sets
number of CPUs to 1. KASan doesn't have such limitation.
DEBUG_PAGEALLOC:
- KASan is slower than DEBUG_PAGEALLOC, but KASan works on sub-page
granularity level, so it able to find more bugs.
SLUB_DEBUG (poisoning, redzones):
- SLUB_DEBUG has lower overhead than KASan.
- SLUB_DEBUG in most cases are not able to detect bad reads,
KASan able to detect both reads and writes.
- In some cases (e.g. redzone overwritten) SLUB_DEBUG detect
bugs only on allocation/freeing of object. KASan catch
bugs right before it will happen, so we always know exact
place of first bad read/write.
[1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel
[2] https://code.google.com/p/address-sanitizer/wiki/FoundBugs
[3] https://code.google.com/p/thread-sanitizer/wiki/FoundBugs
[4] https://code.google.com/p/memory-sanitizer/wiki/FoundBugs
[5] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel#Trophies
Based on work by Andrey Konovalov.
Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Acked-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrey Konovalov <adech.fo@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Serebryany <kcc@google.com>
Cc: Dmitry Chernenkov <dmitryc@google.com>
Cc: Yuri Gribov <tetra2005@gmail.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-13 22:39:17 +00:00
|
|
|
#endif /* CONFIG_KASAN */
|
|
|
|
|
|
2020-12-22 20:02:42 +00:00
|
|
|
#if defined(CONFIG_KASAN) && CONFIG_KASAN_STACK
|
|
|
|
|
void kasan_unpoison_task_stack(struct task_struct *task);
|
|
|
|
|
#else
|
|
|
|
|
static inline void kasan_unpoison_task_stack(struct task_struct *task) {}
|
|
|
|
|
#endif
|
|
|
|
|
|
2018-12-28 08:29:53 +00:00
|
|
|
#ifdef CONFIG_KASAN_GENERIC
|
|
|
|
|
|
|
|
|
|
void kasan_cache_shrink(struct kmem_cache *cache);
|
|
|
|
|
void kasan_cache_shutdown(struct kmem_cache *cache);
|
2020-08-07 06:24:35 +00:00
|
|
|
void kasan_record_aux_stack(void *ptr);
|
2018-12-28 08:29:53 +00:00
|
|
|
|
|
|
|
|
#else /* CONFIG_KASAN_GENERIC */
|
|
|
|
|
|
|
|
|
|
static inline void kasan_cache_shrink(struct kmem_cache *cache) {}
|
|
|
|
|
static inline void kasan_cache_shutdown(struct kmem_cache *cache) {}
|
2020-08-07 06:24:35 +00:00
|
|
|
static inline void kasan_record_aux_stack(void *ptr) {}
|
2018-12-28 08:29:53 +00:00
|
|
|
|
|
|
|
|
#endif /* CONFIG_KASAN_GENERIC */
|
|
|
|
|
|
2020-12-22 20:02:10 +00:00
|
|
|
#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
|
2018-12-28 08:30:16 +00:00
|
|
|
|
2020-12-22 20:02:52 +00:00
|
|
|
static inline void *kasan_reset_tag(const void *addr)
|
|
|
|
|
{
|
|
|
|
|
return (void *)arch_kasan_reset_tag(addr);
|
|
|
|
|
}
|
2018-12-28 08:30:16 +00:00
|
|
|
|
2020-04-02 04:09:37 +00:00
|
|
|
bool kasan_report(unsigned long addr, size_t size,
|
2018-12-28 08:30:54 +00:00
|
|
|
bool is_write, unsigned long ip);
|
|
|
|
|
|
2020-12-22 20:02:10 +00:00
|
|
|
#else /* CONFIG_KASAN_SW_TAGS || CONFIG_KASAN_HW_TAGS */
|
2018-12-28 08:30:16 +00:00
|
|
|
|
|
|
|
|
static inline void *kasan_reset_tag(const void *addr)
|
|
|
|
|
{
|
|
|
|
|
return (void *)addr;
|
|
|
|
|
}
|
|
|
|
|
|
2020-12-22 20:02:10 +00:00
|
|
|
#endif /* CONFIG_KASAN_SW_TAGS || CONFIG_KASAN_HW_TAGS*/
|
|
|
|
|
|
|
|
|
|
#ifdef CONFIG_KASAN_SW_TAGS
|
|
|
|
|
void __init kasan_init_sw_tags(void);
|
|
|
|
|
#else
|
|
|
|
|
static inline void kasan_init_sw_tags(void) { }
|
|
|
|
|
#endif
|
|
|
|
|
|
|
|
|
|
#ifdef CONFIG_KASAN_HW_TAGS
|
|
|
|
|
void kasan_init_hw_tags_cpu(void);
|
|
|
|
|
void __init kasan_init_hw_tags(void);
|
|
|
|
|
#else
|
|
|
|
|
static inline void kasan_init_hw_tags_cpu(void) { }
|
|
|
|
|
static inline void kasan_init_hw_tags(void) { }
|
|
|
|
|
#endif
|
2018-12-28 08:30:09 +00:00
|
|
|
|
kasan: support backing vmalloc space with real shadow memory
Patch series "kasan: support backing vmalloc space with real shadow
memory", v11.
Currently, vmalloc space is backed by the early shadow page. This means
that kasan is incompatible with VMAP_STACK.
This series provides a mechanism to back vmalloc space with real,
dynamically allocated memory. I have only wired up x86, because that's
the only currently supported arch I can work with easily, but it's very
easy to wire up other architectures, and it appears that there is some
work-in-progress code to do this on arm64 and s390.
This has been discussed before in the context of VMAP_STACK:
- https://bugzilla.kernel.org/show_bug.cgi?id=202009
- https://lkml.org/lkml/2018/7/22/198
- https://lkml.org/lkml/2019/7/19/822
In terms of implementation details:
Most mappings in vmalloc space are small, requiring less than a full
page of shadow space. Allocating a full shadow page per mapping would
therefore be wasteful. Furthermore, to ensure that different mappings
use different shadow pages, mappings would have to be aligned to
KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.
Instead, share backing space across multiple mappings. Allocate a
backing page when a mapping in vmalloc space uses a particular page of
the shadow region. This page can be shared by other vmalloc mappings
later on.
We hook in to the vmap infrastructure to lazily clean up unused shadow
memory.
Testing with test_vmalloc.sh on an x86 VM with 2 vCPUs shows that:
- Turning on KASAN, inline instrumentation, without vmalloc, introuduces
a 4.1x-4.2x slowdown in vmalloc operations.
- Turning this on introduces the following slowdowns over KASAN:
* ~1.76x slower single-threaded (test_vmalloc.sh performance)
* ~2.18x slower when both cpus are performing operations
simultaneously (test_vmalloc.sh sequential_test_order=1)
This is unfortunate but given that this is a debug feature only, not the
end of the world. The benchmarks are also a stress-test for the vmalloc
subsystem: they're not indicative of an overall 2x slowdown!
This patch (of 4):
Hook into vmalloc and vmap, and dynamically allocate real shadow memory
to back the mappings.
Most mappings in vmalloc space are small, requiring less than a full
page of shadow space. Allocating a full shadow page per mapping would
therefore be wasteful. Furthermore, to ensure that different mappings
use different shadow pages, mappings would have to be aligned to
KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.
Instead, share backing space across multiple mappings. Allocate a
backing page when a mapping in vmalloc space uses a particular page of
the shadow region. This page can be shared by other vmalloc mappings
later on.
We hook in to the vmap infrastructure to lazily clean up unused shadow
memory.
To avoid the difficulties around swapping mappings around, this code
expects that the part of the shadow region that covers the vmalloc space
will not be covered by the early shadow page, but will be left unmapped.
This will require changes in arch-specific code.
This allows KASAN with VMAP_STACK, and may be helpful for architectures
that do not have a separate module space (e.g. powerpc64, which I am
currently working on). It also allows relaxing the module alignment
back to PAGE_SIZE.
Testing with test_vmalloc.sh on an x86 VM with 2 vCPUs shows that:
- Turning on KASAN, inline instrumentation, without vmalloc, introuduces
a 4.1x-4.2x slowdown in vmalloc operations.
- Turning this on introduces the following slowdowns over KASAN:
* ~1.76x slower single-threaded (test_vmalloc.sh performance)
* ~2.18x slower when both cpus are performing operations
simultaneously (test_vmalloc.sh sequential_test_order=3D1)
This is unfortunate but given that this is a debug feature only, not the
end of the world.
The full benchmark results are:
Performance
No KASAN KASAN original x baseline KASAN vmalloc x baseline x KASAN
fix_size_alloc_test 662004 11404956 17.23 19144610 28.92 1.68
full_fit_alloc_test 710950 12029752 16.92 13184651 18.55 1.10
long_busy_list_alloc_test 9431875 43990172 4.66 82970178 8.80 1.89
random_size_alloc_test 5033626 23061762 4.58 47158834 9.37 2.04
fix_align_alloc_test 1252514 15276910 12.20 31266116 24.96 2.05
random_size_align_alloc_te 1648501 14578321 8.84 25560052 15.51 1.75
align_shift_alloc_test 147 830 5.65 5692 38.72 6.86
pcpu_alloc_test 80732 125520 1.55 140864 1.74 1.12
Total Cycles 119240774314 763211341128 6.40 1390338696894 11.66 1.82
Sequential, 2 cpus
No KASAN KASAN original x baseline KASAN vmalloc x baseline x KASAN
fix_size_alloc_test 1423150 14276550 10.03 27733022 19.49 1.94
full_fit_alloc_test 1754219 14722640 8.39 15030786 8.57 1.02
long_busy_list_alloc_test 11451858 52154973 4.55 107016027 9.34 2.05
random_size_alloc_test 5989020 26735276 4.46 68885923 11.50 2.58
fix_align_alloc_test 2050976 20166900 9.83 50491675 24.62 2.50
random_size_align_alloc_te 2858229 17971700 6.29 38730225 13.55 2.16
align_shift_alloc_test 405 6428 15.87 26253 64.82 4.08
pcpu_alloc_test 127183 151464 1.19 216263 1.70 1.43
Total Cycles 54181269392 308723699764 5.70 650772566394 12.01 2.11
fix_size_alloc_test 1420404 14289308 10.06 27790035 19.56 1.94
full_fit_alloc_test 1736145 14806234 8.53 15274301 8.80 1.03
long_busy_list_alloc_test 11404638 52270785 4.58 107550254 9.43 2.06
random_size_alloc_test 6017006 26650625 4.43 68696127 11.42 2.58
fix_align_alloc_test 2045504 20280985 9.91 50414862 24.65 2.49
random_size_align_alloc_te 2845338 17931018 6.30 38510276 13.53 2.15
align_shift_alloc_test 472 3760 7.97 9656 20.46 2.57
pcpu_alloc_test 118643 132732 1.12 146504 1.23 1.10
Total Cycles 54040011688 309102805492 5.72 651325675652 12.05 2.11
[dja@axtens.net: fixups]
Link: http://lkml.kernel.org/r/20191120052719.7201-1-dja@axtens.net
Link: https://bugzilla.kernel.org/show_bug.cgi?id=3D202009
Link: http://lkml.kernel.org/r/20191031093909.9228-2-dja@axtens.net
Signed-off-by: Mark Rutland <mark.rutland@arm.com> [shadow rework]
Signed-off-by: Daniel Axtens <dja@axtens.net>
Co-developed-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-12-01 01:54:50 +00:00
|
|
|
#ifdef CONFIG_KASAN_VMALLOC
|
2020-12-22 20:00:14 +00:00
|
|
|
|
2019-12-18 04:51:38 +00:00
|
|
|
int kasan_populate_vmalloc(unsigned long addr, unsigned long size);
|
|
|
|
|
void kasan_poison_vmalloc(const void *start, unsigned long size);
|
|
|
|
|
void kasan_unpoison_vmalloc(const void *start, unsigned long size);
|
kasan: support backing vmalloc space with real shadow memory
Patch series "kasan: support backing vmalloc space with real shadow
memory", v11.
Currently, vmalloc space is backed by the early shadow page. This means
that kasan is incompatible with VMAP_STACK.
This series provides a mechanism to back vmalloc space with real,
dynamically allocated memory. I have only wired up x86, because that's
the only currently supported arch I can work with easily, but it's very
easy to wire up other architectures, and it appears that there is some
work-in-progress code to do this on arm64 and s390.
This has been discussed before in the context of VMAP_STACK:
- https://bugzilla.kernel.org/show_bug.cgi?id=202009
- https://lkml.org/lkml/2018/7/22/198
- https://lkml.org/lkml/2019/7/19/822
In terms of implementation details:
Most mappings in vmalloc space are small, requiring less than a full
page of shadow space. Allocating a full shadow page per mapping would
therefore be wasteful. Furthermore, to ensure that different mappings
use different shadow pages, mappings would have to be aligned to
KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.
Instead, share backing space across multiple mappings. Allocate a
backing page when a mapping in vmalloc space uses a particular page of
the shadow region. This page can be shared by other vmalloc mappings
later on.
We hook in to the vmap infrastructure to lazily clean up unused shadow
memory.
Testing with test_vmalloc.sh on an x86 VM with 2 vCPUs shows that:
- Turning on KASAN, inline instrumentation, without vmalloc, introuduces
a 4.1x-4.2x slowdown in vmalloc operations.
- Turning this on introduces the following slowdowns over KASAN:
* ~1.76x slower single-threaded (test_vmalloc.sh performance)
* ~2.18x slower when both cpus are performing operations
simultaneously (test_vmalloc.sh sequential_test_order=1)
This is unfortunate but given that this is a debug feature only, not the
end of the world. The benchmarks are also a stress-test for the vmalloc
subsystem: they're not indicative of an overall 2x slowdown!
This patch (of 4):
Hook into vmalloc and vmap, and dynamically allocate real shadow memory
to back the mappings.
Most mappings in vmalloc space are small, requiring less than a full
page of shadow space. Allocating a full shadow page per mapping would
therefore be wasteful. Furthermore, to ensure that different mappings
use different shadow pages, mappings would have to be aligned to
KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.
Instead, share backing space across multiple mappings. Allocate a
backing page when a mapping in vmalloc space uses a particular page of
the shadow region. This page can be shared by other vmalloc mappings
later on.
We hook in to the vmap infrastructure to lazily clean up unused shadow
memory.
To avoid the difficulties around swapping mappings around, this code
expects that the part of the shadow region that covers the vmalloc space
will not be covered by the early shadow page, but will be left unmapped.
This will require changes in arch-specific code.
This allows KASAN with VMAP_STACK, and may be helpful for architectures
that do not have a separate module space (e.g. powerpc64, which I am
currently working on). It also allows relaxing the module alignment
back to PAGE_SIZE.
Testing with test_vmalloc.sh on an x86 VM with 2 vCPUs shows that:
- Turning on KASAN, inline instrumentation, without vmalloc, introuduces
a 4.1x-4.2x slowdown in vmalloc operations.
- Turning this on introduces the following slowdowns over KASAN:
* ~1.76x slower single-threaded (test_vmalloc.sh performance)
* ~2.18x slower when both cpus are performing operations
simultaneously (test_vmalloc.sh sequential_test_order=3D1)
This is unfortunate but given that this is a debug feature only, not the
end of the world.
The full benchmark results are:
Performance
No KASAN KASAN original x baseline KASAN vmalloc x baseline x KASAN
fix_size_alloc_test 662004 11404956 17.23 19144610 28.92 1.68
full_fit_alloc_test 710950 12029752 16.92 13184651 18.55 1.10
long_busy_list_alloc_test 9431875 43990172 4.66 82970178 8.80 1.89
random_size_alloc_test 5033626 23061762 4.58 47158834 9.37 2.04
fix_align_alloc_test 1252514 15276910 12.20 31266116 24.96 2.05
random_size_align_alloc_te 1648501 14578321 8.84 25560052 15.51 1.75
align_shift_alloc_test 147 830 5.65 5692 38.72 6.86
pcpu_alloc_test 80732 125520 1.55 140864 1.74 1.12
Total Cycles 119240774314 763211341128 6.40 1390338696894 11.66 1.82
Sequential, 2 cpus
No KASAN KASAN original x baseline KASAN vmalloc x baseline x KASAN
fix_size_alloc_test 1423150 14276550 10.03 27733022 19.49 1.94
full_fit_alloc_test 1754219 14722640 8.39 15030786 8.57 1.02
long_busy_list_alloc_test 11451858 52154973 4.55 107016027 9.34 2.05
random_size_alloc_test 5989020 26735276 4.46 68885923 11.50 2.58
fix_align_alloc_test 2050976 20166900 9.83 50491675 24.62 2.50
random_size_align_alloc_te 2858229 17971700 6.29 38730225 13.55 2.16
align_shift_alloc_test 405 6428 15.87 26253 64.82 4.08
pcpu_alloc_test 127183 151464 1.19 216263 1.70 1.43
Total Cycles 54181269392 308723699764 5.70 650772566394 12.01 2.11
fix_size_alloc_test 1420404 14289308 10.06 27790035 19.56 1.94
full_fit_alloc_test 1736145 14806234 8.53 15274301 8.80 1.03
long_busy_list_alloc_test 11404638 52270785 4.58 107550254 9.43 2.06
random_size_alloc_test 6017006 26650625 4.43 68696127 11.42 2.58
fix_align_alloc_test 2045504 20280985 9.91 50414862 24.65 2.49
random_size_align_alloc_te 2845338 17931018 6.30 38510276 13.53 2.15
align_shift_alloc_test 472 3760 7.97 9656 20.46 2.57
pcpu_alloc_test 118643 132732 1.12 146504 1.23 1.10
Total Cycles 54040011688 309102805492 5.72 651325675652 12.05 2.11
[dja@axtens.net: fixups]
Link: http://lkml.kernel.org/r/20191120052719.7201-1-dja@axtens.net
Link: https://bugzilla.kernel.org/show_bug.cgi?id=3D202009
Link: http://lkml.kernel.org/r/20191031093909.9228-2-dja@axtens.net
Signed-off-by: Mark Rutland <mark.rutland@arm.com> [shadow rework]
Signed-off-by: Daniel Axtens <dja@axtens.net>
Co-developed-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-12-01 01:54:50 +00:00
|
|
|
void kasan_release_vmalloc(unsigned long start, unsigned long end,
|
|
|
|
|
unsigned long free_region_start,
|
|
|
|
|
unsigned long free_region_end);
|
2020-12-22 20:00:14 +00:00
|
|
|
|
|
|
|
|
#else /* CONFIG_KASAN_VMALLOC */
|
|
|
|
|
|
2019-12-18 04:51:38 +00:00
|
|
|
static inline int kasan_populate_vmalloc(unsigned long start,
|
|
|
|
|
unsigned long size)
|
kasan: support backing vmalloc space with real shadow memory
Patch series "kasan: support backing vmalloc space with real shadow
memory", v11.
Currently, vmalloc space is backed by the early shadow page. This means
that kasan is incompatible with VMAP_STACK.
This series provides a mechanism to back vmalloc space with real,
dynamically allocated memory. I have only wired up x86, because that's
the only currently supported arch I can work with easily, but it's very
easy to wire up other architectures, and it appears that there is some
work-in-progress code to do this on arm64 and s390.
This has been discussed before in the context of VMAP_STACK:
- https://bugzilla.kernel.org/show_bug.cgi?id=202009
- https://lkml.org/lkml/2018/7/22/198
- https://lkml.org/lkml/2019/7/19/822
In terms of implementation details:
Most mappings in vmalloc space are small, requiring less than a full
page of shadow space. Allocating a full shadow page per mapping would
therefore be wasteful. Furthermore, to ensure that different mappings
use different shadow pages, mappings would have to be aligned to
KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.
Instead, share backing space across multiple mappings. Allocate a
backing page when a mapping in vmalloc space uses a particular page of
the shadow region. This page can be shared by other vmalloc mappings
later on.
We hook in to the vmap infrastructure to lazily clean up unused shadow
memory.
Testing with test_vmalloc.sh on an x86 VM with 2 vCPUs shows that:
- Turning on KASAN, inline instrumentation, without vmalloc, introuduces
a 4.1x-4.2x slowdown in vmalloc operations.
- Turning this on introduces the following slowdowns over KASAN:
* ~1.76x slower single-threaded (test_vmalloc.sh performance)
* ~2.18x slower when both cpus are performing operations
simultaneously (test_vmalloc.sh sequential_test_order=1)
This is unfortunate but given that this is a debug feature only, not the
end of the world. The benchmarks are also a stress-test for the vmalloc
subsystem: they're not indicative of an overall 2x slowdown!
This patch (of 4):
Hook into vmalloc and vmap, and dynamically allocate real shadow memory
to back the mappings.
Most mappings in vmalloc space are small, requiring less than a full
page of shadow space. Allocating a full shadow page per mapping would
therefore be wasteful. Furthermore, to ensure that different mappings
use different shadow pages, mappings would have to be aligned to
KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.
Instead, share backing space across multiple mappings. Allocate a
backing page when a mapping in vmalloc space uses a particular page of
the shadow region. This page can be shared by other vmalloc mappings
later on.
We hook in to the vmap infrastructure to lazily clean up unused shadow
memory.
To avoid the difficulties around swapping mappings around, this code
expects that the part of the shadow region that covers the vmalloc space
will not be covered by the early shadow page, but will be left unmapped.
This will require changes in arch-specific code.
This allows KASAN with VMAP_STACK, and may be helpful for architectures
that do not have a separate module space (e.g. powerpc64, which I am
currently working on). It also allows relaxing the module alignment
back to PAGE_SIZE.
Testing with test_vmalloc.sh on an x86 VM with 2 vCPUs shows that:
- Turning on KASAN, inline instrumentation, without vmalloc, introuduces
a 4.1x-4.2x slowdown in vmalloc operations.
- Turning this on introduces the following slowdowns over KASAN:
* ~1.76x slower single-threaded (test_vmalloc.sh performance)
* ~2.18x slower when both cpus are performing operations
simultaneously (test_vmalloc.sh sequential_test_order=3D1)
This is unfortunate but given that this is a debug feature only, not the
end of the world.
The full benchmark results are:
Performance
No KASAN KASAN original x baseline KASAN vmalloc x baseline x KASAN
fix_size_alloc_test 662004 11404956 17.23 19144610 28.92 1.68
full_fit_alloc_test 710950 12029752 16.92 13184651 18.55 1.10
long_busy_list_alloc_test 9431875 43990172 4.66 82970178 8.80 1.89
random_size_alloc_test 5033626 23061762 4.58 47158834 9.37 2.04
fix_align_alloc_test 1252514 15276910 12.20 31266116 24.96 2.05
random_size_align_alloc_te 1648501 14578321 8.84 25560052 15.51 1.75
align_shift_alloc_test 147 830 5.65 5692 38.72 6.86
pcpu_alloc_test 80732 125520 1.55 140864 1.74 1.12
Total Cycles 119240774314 763211341128 6.40 1390338696894 11.66 1.82
Sequential, 2 cpus
No KASAN KASAN original x baseline KASAN vmalloc x baseline x KASAN
fix_size_alloc_test 1423150 14276550 10.03 27733022 19.49 1.94
full_fit_alloc_test 1754219 14722640 8.39 15030786 8.57 1.02
long_busy_list_alloc_test 11451858 52154973 4.55 107016027 9.34 2.05
random_size_alloc_test 5989020 26735276 4.46 68885923 11.50 2.58
fix_align_alloc_test 2050976 20166900 9.83 50491675 24.62 2.50
random_size_align_alloc_te 2858229 17971700 6.29 38730225 13.55 2.16
align_shift_alloc_test 405 6428 15.87 26253 64.82 4.08
pcpu_alloc_test 127183 151464 1.19 216263 1.70 1.43
Total Cycles 54181269392 308723699764 5.70 650772566394 12.01 2.11
fix_size_alloc_test 1420404 14289308 10.06 27790035 19.56 1.94
full_fit_alloc_test 1736145 14806234 8.53 15274301 8.80 1.03
long_busy_list_alloc_test 11404638 52270785 4.58 107550254 9.43 2.06
random_size_alloc_test 6017006 26650625 4.43 68696127 11.42 2.58
fix_align_alloc_test 2045504 20280985 9.91 50414862 24.65 2.49
random_size_align_alloc_te 2845338 17931018 6.30 38510276 13.53 2.15
align_shift_alloc_test 472 3760 7.97 9656 20.46 2.57
pcpu_alloc_test 118643 132732 1.12 146504 1.23 1.10
Total Cycles 54040011688 309102805492 5.72 651325675652 12.05 2.11
[dja@axtens.net: fixups]
Link: http://lkml.kernel.org/r/20191120052719.7201-1-dja@axtens.net
Link: https://bugzilla.kernel.org/show_bug.cgi?id=3D202009
Link: http://lkml.kernel.org/r/20191031093909.9228-2-dja@axtens.net
Signed-off-by: Mark Rutland <mark.rutland@arm.com> [shadow rework]
Signed-off-by: Daniel Axtens <dja@axtens.net>
Co-developed-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-12-01 01:54:50 +00:00
|
|
|
{
|
|
|
|
|
return 0;
|
|
|
|
|
}
|
|
|
|
|
|
2019-12-18 04:51:38 +00:00
|
|
|
static inline void kasan_poison_vmalloc(const void *start, unsigned long size)
|
|
|
|
|
{ }
|
|
|
|
|
static inline void kasan_unpoison_vmalloc(const void *start, unsigned long size)
|
|
|
|
|
{ }
|
kasan: support backing vmalloc space with real shadow memory
Patch series "kasan: support backing vmalloc space with real shadow
memory", v11.
Currently, vmalloc space is backed by the early shadow page. This means
that kasan is incompatible with VMAP_STACK.
This series provides a mechanism to back vmalloc space with real,
dynamically allocated memory. I have only wired up x86, because that's
the only currently supported arch I can work with easily, but it's very
easy to wire up other architectures, and it appears that there is some
work-in-progress code to do this on arm64 and s390.
This has been discussed before in the context of VMAP_STACK:
- https://bugzilla.kernel.org/show_bug.cgi?id=202009
- https://lkml.org/lkml/2018/7/22/198
- https://lkml.org/lkml/2019/7/19/822
In terms of implementation details:
Most mappings in vmalloc space are small, requiring less than a full
page of shadow space. Allocating a full shadow page per mapping would
therefore be wasteful. Furthermore, to ensure that different mappings
use different shadow pages, mappings would have to be aligned to
KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.
Instead, share backing space across multiple mappings. Allocate a
backing page when a mapping in vmalloc space uses a particular page of
the shadow region. This page can be shared by other vmalloc mappings
later on.
We hook in to the vmap infrastructure to lazily clean up unused shadow
memory.
Testing with test_vmalloc.sh on an x86 VM with 2 vCPUs shows that:
- Turning on KASAN, inline instrumentation, without vmalloc, introuduces
a 4.1x-4.2x slowdown in vmalloc operations.
- Turning this on introduces the following slowdowns over KASAN:
* ~1.76x slower single-threaded (test_vmalloc.sh performance)
* ~2.18x slower when both cpus are performing operations
simultaneously (test_vmalloc.sh sequential_test_order=1)
This is unfortunate but given that this is a debug feature only, not the
end of the world. The benchmarks are also a stress-test for the vmalloc
subsystem: they're not indicative of an overall 2x slowdown!
This patch (of 4):
Hook into vmalloc and vmap, and dynamically allocate real shadow memory
to back the mappings.
Most mappings in vmalloc space are small, requiring less than a full
page of shadow space. Allocating a full shadow page per mapping would
therefore be wasteful. Furthermore, to ensure that different mappings
use different shadow pages, mappings would have to be aligned to
KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.
Instead, share backing space across multiple mappings. Allocate a
backing page when a mapping in vmalloc space uses a particular page of
the shadow region. This page can be shared by other vmalloc mappings
later on.
We hook in to the vmap infrastructure to lazily clean up unused shadow
memory.
To avoid the difficulties around swapping mappings around, this code
expects that the part of the shadow region that covers the vmalloc space
will not be covered by the early shadow page, but will be left unmapped.
This will require changes in arch-specific code.
This allows KASAN with VMAP_STACK, and may be helpful for architectures
that do not have a separate module space (e.g. powerpc64, which I am
currently working on). It also allows relaxing the module alignment
back to PAGE_SIZE.
Testing with test_vmalloc.sh on an x86 VM with 2 vCPUs shows that:
- Turning on KASAN, inline instrumentation, without vmalloc, introuduces
a 4.1x-4.2x slowdown in vmalloc operations.
- Turning this on introduces the following slowdowns over KASAN:
* ~1.76x slower single-threaded (test_vmalloc.sh performance)
* ~2.18x slower when both cpus are performing operations
simultaneously (test_vmalloc.sh sequential_test_order=3D1)
This is unfortunate but given that this is a debug feature only, not the
end of the world.
The full benchmark results are:
Performance
No KASAN KASAN original x baseline KASAN vmalloc x baseline x KASAN
fix_size_alloc_test 662004 11404956 17.23 19144610 28.92 1.68
full_fit_alloc_test 710950 12029752 16.92 13184651 18.55 1.10
long_busy_list_alloc_test 9431875 43990172 4.66 82970178 8.80 1.89
random_size_alloc_test 5033626 23061762 4.58 47158834 9.37 2.04
fix_align_alloc_test 1252514 15276910 12.20 31266116 24.96 2.05
random_size_align_alloc_te 1648501 14578321 8.84 25560052 15.51 1.75
align_shift_alloc_test 147 830 5.65 5692 38.72 6.86
pcpu_alloc_test 80732 125520 1.55 140864 1.74 1.12
Total Cycles 119240774314 763211341128 6.40 1390338696894 11.66 1.82
Sequential, 2 cpus
No KASAN KASAN original x baseline KASAN vmalloc x baseline x KASAN
fix_size_alloc_test 1423150 14276550 10.03 27733022 19.49 1.94
full_fit_alloc_test 1754219 14722640 8.39 15030786 8.57 1.02
long_busy_list_alloc_test 11451858 52154973 4.55 107016027 9.34 2.05
random_size_alloc_test 5989020 26735276 4.46 68885923 11.50 2.58
fix_align_alloc_test 2050976 20166900 9.83 50491675 24.62 2.50
random_size_align_alloc_te 2858229 17971700 6.29 38730225 13.55 2.16
align_shift_alloc_test 405 6428 15.87 26253 64.82 4.08
pcpu_alloc_test 127183 151464 1.19 216263 1.70 1.43
Total Cycles 54181269392 308723699764 5.70 650772566394 12.01 2.11
fix_size_alloc_test 1420404 14289308 10.06 27790035 19.56 1.94
full_fit_alloc_test 1736145 14806234 8.53 15274301 8.80 1.03
long_busy_list_alloc_test 11404638 52270785 4.58 107550254 9.43 2.06
random_size_alloc_test 6017006 26650625 4.43 68696127 11.42 2.58
fix_align_alloc_test 2045504 20280985 9.91 50414862 24.65 2.49
random_size_align_alloc_te 2845338 17931018 6.30 38510276 13.53 2.15
align_shift_alloc_test 472 3760 7.97 9656 20.46 2.57
pcpu_alloc_test 118643 132732 1.12 146504 1.23 1.10
Total Cycles 54040011688 309102805492 5.72 651325675652 12.05 2.11
[dja@axtens.net: fixups]
Link: http://lkml.kernel.org/r/20191120052719.7201-1-dja@axtens.net
Link: https://bugzilla.kernel.org/show_bug.cgi?id=3D202009
Link: http://lkml.kernel.org/r/20191031093909.9228-2-dja@axtens.net
Signed-off-by: Mark Rutland <mark.rutland@arm.com> [shadow rework]
Signed-off-by: Daniel Axtens <dja@axtens.net>
Co-developed-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-12-01 01:54:50 +00:00
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static inline void kasan_release_vmalloc(unsigned long start,
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unsigned long end,
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unsigned long free_region_start,
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unsigned long free_region_end) {}
|
2020-12-22 20:00:14 +00:00
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#endif /* CONFIG_KASAN_VMALLOC */
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2020-12-22 20:02:06 +00:00
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#if (defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)) && \
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!defined(CONFIG_KASAN_VMALLOC)
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2020-12-22 20:00:14 +00:00
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/*
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* These functions provide a special case to support backing module
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* allocations with real shadow memory. With KASAN vmalloc, the special
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* case is unnecessary, as the work is handled in the generic case.
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*/
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int kasan_module_alloc(void *addr, size_t size);
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void kasan_free_shadow(const struct vm_struct *vm);
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2020-12-22 20:02:06 +00:00
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#else /* (CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS) && !CONFIG_KASAN_VMALLOC */
|
2020-12-22 20:00:14 +00:00
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static inline int kasan_module_alloc(void *addr, size_t size) { return 0; }
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static inline void kasan_free_shadow(const struct vm_struct *vm) {}
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2020-12-22 20:02:06 +00:00
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#endif /* (CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS) && !CONFIG_KASAN_VMALLOC */
|
kasan: support backing vmalloc space with real shadow memory
Patch series "kasan: support backing vmalloc space with real shadow
memory", v11.
Currently, vmalloc space is backed by the early shadow page. This means
that kasan is incompatible with VMAP_STACK.
This series provides a mechanism to back vmalloc space with real,
dynamically allocated memory. I have only wired up x86, because that's
the only currently supported arch I can work with easily, but it's very
easy to wire up other architectures, and it appears that there is some
work-in-progress code to do this on arm64 and s390.
This has been discussed before in the context of VMAP_STACK:
- https://bugzilla.kernel.org/show_bug.cgi?id=202009
- https://lkml.org/lkml/2018/7/22/198
- https://lkml.org/lkml/2019/7/19/822
In terms of implementation details:
Most mappings in vmalloc space are small, requiring less than a full
page of shadow space. Allocating a full shadow page per mapping would
therefore be wasteful. Furthermore, to ensure that different mappings
use different shadow pages, mappings would have to be aligned to
KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.
Instead, share backing space across multiple mappings. Allocate a
backing page when a mapping in vmalloc space uses a particular page of
the shadow region. This page can be shared by other vmalloc mappings
later on.
We hook in to the vmap infrastructure to lazily clean up unused shadow
memory.
Testing with test_vmalloc.sh on an x86 VM with 2 vCPUs shows that:
- Turning on KASAN, inline instrumentation, without vmalloc, introuduces
a 4.1x-4.2x slowdown in vmalloc operations.
- Turning this on introduces the following slowdowns over KASAN:
* ~1.76x slower single-threaded (test_vmalloc.sh performance)
* ~2.18x slower when both cpus are performing operations
simultaneously (test_vmalloc.sh sequential_test_order=1)
This is unfortunate but given that this is a debug feature only, not the
end of the world. The benchmarks are also a stress-test for the vmalloc
subsystem: they're not indicative of an overall 2x slowdown!
This patch (of 4):
Hook into vmalloc and vmap, and dynamically allocate real shadow memory
to back the mappings.
Most mappings in vmalloc space are small, requiring less than a full
page of shadow space. Allocating a full shadow page per mapping would
therefore be wasteful. Furthermore, to ensure that different mappings
use different shadow pages, mappings would have to be aligned to
KASAN_SHADOW_SCALE_SIZE * PAGE_SIZE.
Instead, share backing space across multiple mappings. Allocate a
backing page when a mapping in vmalloc space uses a particular page of
the shadow region. This page can be shared by other vmalloc mappings
later on.
We hook in to the vmap infrastructure to lazily clean up unused shadow
memory.
To avoid the difficulties around swapping mappings around, this code
expects that the part of the shadow region that covers the vmalloc space
will not be covered by the early shadow page, but will be left unmapped.
This will require changes in arch-specific code.
This allows KASAN with VMAP_STACK, and may be helpful for architectures
that do not have a separate module space (e.g. powerpc64, which I am
currently working on). It also allows relaxing the module alignment
back to PAGE_SIZE.
Testing with test_vmalloc.sh on an x86 VM with 2 vCPUs shows that:
- Turning on KASAN, inline instrumentation, without vmalloc, introuduces
a 4.1x-4.2x slowdown in vmalloc operations.
- Turning this on introduces the following slowdowns over KASAN:
* ~1.76x slower single-threaded (test_vmalloc.sh performance)
* ~2.18x slower when both cpus are performing operations
simultaneously (test_vmalloc.sh sequential_test_order=3D1)
This is unfortunate but given that this is a debug feature only, not the
end of the world.
The full benchmark results are:
Performance
No KASAN KASAN original x baseline KASAN vmalloc x baseline x KASAN
fix_size_alloc_test 662004 11404956 17.23 19144610 28.92 1.68
full_fit_alloc_test 710950 12029752 16.92 13184651 18.55 1.10
long_busy_list_alloc_test 9431875 43990172 4.66 82970178 8.80 1.89
random_size_alloc_test 5033626 23061762 4.58 47158834 9.37 2.04
fix_align_alloc_test 1252514 15276910 12.20 31266116 24.96 2.05
random_size_align_alloc_te 1648501 14578321 8.84 25560052 15.51 1.75
align_shift_alloc_test 147 830 5.65 5692 38.72 6.86
pcpu_alloc_test 80732 125520 1.55 140864 1.74 1.12
Total Cycles 119240774314 763211341128 6.40 1390338696894 11.66 1.82
Sequential, 2 cpus
No KASAN KASAN original x baseline KASAN vmalloc x baseline x KASAN
fix_size_alloc_test 1423150 14276550 10.03 27733022 19.49 1.94
full_fit_alloc_test 1754219 14722640 8.39 15030786 8.57 1.02
long_busy_list_alloc_test 11451858 52154973 4.55 107016027 9.34 2.05
random_size_alloc_test 5989020 26735276 4.46 68885923 11.50 2.58
fix_align_alloc_test 2050976 20166900 9.83 50491675 24.62 2.50
random_size_align_alloc_te 2858229 17971700 6.29 38730225 13.55 2.16
align_shift_alloc_test 405 6428 15.87 26253 64.82 4.08
pcpu_alloc_test 127183 151464 1.19 216263 1.70 1.43
Total Cycles 54181269392 308723699764 5.70 650772566394 12.01 2.11
fix_size_alloc_test 1420404 14289308 10.06 27790035 19.56 1.94
full_fit_alloc_test 1736145 14806234 8.53 15274301 8.80 1.03
long_busy_list_alloc_test 11404638 52270785 4.58 107550254 9.43 2.06
random_size_alloc_test 6017006 26650625 4.43 68696127 11.42 2.58
fix_align_alloc_test 2045504 20280985 9.91 50414862 24.65 2.49
random_size_align_alloc_te 2845338 17931018 6.30 38510276 13.53 2.15
align_shift_alloc_test 472 3760 7.97 9656 20.46 2.57
pcpu_alloc_test 118643 132732 1.12 146504 1.23 1.10
Total Cycles 54040011688 309102805492 5.72 651325675652 12.05 2.11
[dja@axtens.net: fixups]
Link: http://lkml.kernel.org/r/20191120052719.7201-1-dja@axtens.net
Link: https://bugzilla.kernel.org/show_bug.cgi?id=3D202009
Link: http://lkml.kernel.org/r/20191031093909.9228-2-dja@axtens.net
Signed-off-by: Mark Rutland <mark.rutland@arm.com> [shadow rework]
Signed-off-by: Daniel Axtens <dja@axtens.net>
Co-developed-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: Qian Cai <cai@lca.pw>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-12-01 01:54:50 +00:00
|
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|
|
2019-12-18 23:11:50 +00:00
|
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#ifdef CONFIG_KASAN_INLINE
|
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void kasan_non_canonical_hook(unsigned long addr);
|
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|
#else /* CONFIG_KASAN_INLINE */
|
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|
static inline void kasan_non_canonical_hook(unsigned long addr) { }
|
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|
|
#endif /* CONFIG_KASAN_INLINE */
|
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|
kasan: add kernel address sanitizer infrastructure
Kernel Address sanitizer (KASan) is a dynamic memory error detector. It
provides fast and comprehensive solution for finding use-after-free and
out-of-bounds bugs.
KASAN uses compile-time instrumentation for checking every memory access,
therefore GCC > v4.9.2 required. v4.9.2 almost works, but has issues with
putting symbol aliases into the wrong section, which breaks kasan
instrumentation of globals.
This patch only adds infrastructure for kernel address sanitizer. It's
not available for use yet. The idea and some code was borrowed from [1].
Basic idea:
The main idea of KASAN is to use shadow memory to record whether each byte
of memory is safe to access or not, and use compiler's instrumentation to
check the shadow memory on each memory access.
Address sanitizer uses 1/8 of the memory addressable in kernel for shadow
memory and uses direct mapping with a scale and offset to translate a
memory address to its corresponding shadow address.
Here is function to translate address to corresponding shadow address:
unsigned long kasan_mem_to_shadow(unsigned long addr)
{
return (addr >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET;
}
where KASAN_SHADOW_SCALE_SHIFT = 3.
So for every 8 bytes there is one corresponding byte of shadow memory.
The following encoding used for each shadow byte: 0 means that all 8 bytes
of the corresponding memory region are valid for access; k (1 <= k <= 7)
means that the first k bytes are valid for access, and other (8 - k) bytes
are not; Any negative value indicates that the entire 8-bytes are
inaccessible. Different negative values used to distinguish between
different kinds of inaccessible memory (redzones, freed memory) (see
mm/kasan/kasan.h).
To be able to detect accesses to bad memory we need a special compiler.
Such compiler inserts a specific function calls (__asan_load*(addr),
__asan_store*(addr)) before each memory access of size 1, 2, 4, 8 or 16.
These functions check whether memory region is valid to access or not by
checking corresponding shadow memory. If access is not valid an error
printed.
Historical background of the address sanitizer from Dmitry Vyukov:
"We've developed the set of tools, AddressSanitizer (Asan),
ThreadSanitizer and MemorySanitizer, for user space. We actively use
them for testing inside of Google (continuous testing, fuzzing,
running prod services). To date the tools have found more than 10'000
scary bugs in Chromium, Google internal codebase and various
open-source projects (Firefox, OpenSSL, gcc, clang, ffmpeg, MySQL and
lots of others): [2] [3] [4].
The tools are part of both gcc and clang compilers.
We have not yet done massive testing under the Kernel AddressSanitizer
(it's kind of chicken and egg problem, you need it to be upstream to
start applying it extensively). To date it has found about 50 bugs.
Bugs that we've found in upstream kernel are listed in [5].
We've also found ~20 bugs in out internal version of the kernel. Also
people from Samsung and Oracle have found some.
[...]
As others noted, the main feature of AddressSanitizer is its
performance due to inline compiler instrumentation and simple linear
shadow memory. User-space Asan has ~2x slowdown on computational
programs and ~2x memory consumption increase. Taking into account that
kernel usually consumes only small fraction of CPU and memory when
running real user-space programs, I would expect that kernel Asan will
have ~10-30% slowdown and similar memory consumption increase (when we
finish all tuning).
I agree that Asan can well replace kmemcheck. We have plans to start
working on Kernel MemorySanitizer that finds uses of unitialized
memory. Asan+Msan will provide feature-parity with kmemcheck. As
others noted, Asan will unlikely replace debug slab and pagealloc that
can be enabled at runtime. Asan uses compiler instrumentation, so even
if it is disabled, it still incurs visible overheads.
Asan technology is easily portable to other architectures. Compiler
instrumentation is fully portable. Runtime has some arch-dependent
parts like shadow mapping and atomic operation interception. They are
relatively easy to port."
Comparison with other debugging features:
========================================
KMEMCHECK:
- KASan can do almost everything that kmemcheck can. KASan uses
compile-time instrumentation, which makes it significantly faster than
kmemcheck. The only advantage of kmemcheck over KASan is detection of
uninitialized memory reads.
Some brief performance testing showed that kasan could be
x500-x600 times faster than kmemcheck:
$ netperf -l 30
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to localhost (127.0.0.1) port 0 AF_INET
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec
no debug: 87380 16384 16384 30.00 41624.72
kasan inline: 87380 16384 16384 30.00 12870.54
kasan outline: 87380 16384 16384 30.00 10586.39
kmemcheck: 87380 16384 16384 30.03 20.23
- Also kmemcheck couldn't work on several CPUs. It always sets
number of CPUs to 1. KASan doesn't have such limitation.
DEBUG_PAGEALLOC:
- KASan is slower than DEBUG_PAGEALLOC, but KASan works on sub-page
granularity level, so it able to find more bugs.
SLUB_DEBUG (poisoning, redzones):
- SLUB_DEBUG has lower overhead than KASan.
- SLUB_DEBUG in most cases are not able to detect bad reads,
KASan able to detect both reads and writes.
- In some cases (e.g. redzone overwritten) SLUB_DEBUG detect
bugs only on allocation/freeing of object. KASan catch
bugs right before it will happen, so we always know exact
place of first bad read/write.
[1] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel
[2] https://code.google.com/p/address-sanitizer/wiki/FoundBugs
[3] https://code.google.com/p/thread-sanitizer/wiki/FoundBugs
[4] https://code.google.com/p/memory-sanitizer/wiki/FoundBugs
[5] https://code.google.com/p/address-sanitizer/wiki/AddressSanitizerForKernel#Trophies
Based on work by Andrey Konovalov.
Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
Acked-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrey Konovalov <adech.fo@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Konstantin Serebryany <kcc@google.com>
Cc: Dmitry Chernenkov <dmitryc@google.com>
Cc: Yuri Gribov <tetra2005@gmail.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-02-13 22:39:17 +00:00
|
|
|
#endif /* LINUX_KASAN_H */
|