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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
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cf68fffb66
This change adds support for Clang’s forward-edge Control Flow Integrity (CFI) checking. With CONFIG_CFI_CLANG, the compiler injects a runtime check before each indirect function call to ensure the target is a valid function with the correct static type. This restricts possible call targets and makes it more difficult for an attacker to exploit bugs that allow the modification of stored function pointers. For more details, see: https://clang.llvm.org/docs/ControlFlowIntegrity.html Clang requires CONFIG_LTO_CLANG to be enabled with CFI to gain visibility to possible call targets. Kernel modules are supported with Clang’s cross-DSO CFI mode, which allows checking between independently compiled components. With CFI enabled, the compiler injects a __cfi_check() function into the kernel and each module for validating local call targets. For cross-module calls that cannot be validated locally, the compiler calls the global __cfi_slowpath_diag() function, which determines the target module and calls the correct __cfi_check() function. This patch includes a slowpath implementation that uses __module_address() to resolve call targets, and with CONFIG_CFI_CLANG_SHADOW enabled, a shadow map that speeds up module look-ups by ~3x. Clang implements indirect call checking using jump tables and offers two methods of generating them. With canonical jump tables, the compiler renames each address-taken function to <function>.cfi and points the original symbol to a jump table entry, which passes __cfi_check() validation. This isn’t compatible with stand-alone assembly code, which the compiler doesn’t instrument, and would result in indirect calls to assembly code to fail. Therefore, we default to using non-canonical jump tables instead, where the compiler generates a local jump table entry <function>.cfi_jt for each address-taken function, and replaces all references to the function with the address of the jump table entry. Note that because non-canonical jump table addresses are local to each component, they break cross-module function address equality. Specifically, the address of a global function will be different in each module, as it's replaced with the address of a local jump table entry. If this address is passed to a different module, it won’t match the address of the same function taken there. This may break code that relies on comparing addresses passed from other components. CFI checking can be disabled in a function with the __nocfi attribute. Additionally, CFI can be disabled for an entire compilation unit by filtering out CC_FLAGS_CFI. By default, CFI failures result in a kernel panic to stop a potential exploit. CONFIG_CFI_PERMISSIVE enables a permissive mode, where the kernel prints out a rate-limited warning instead, and allows execution to continue. This option is helpful for locating type mismatches, but should only be enabled during development. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> Reviewed-by: Kees Cook <keescook@chromium.org> Tested-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20210408182843.1754385-2-samitolvanen@google.com
262 lines
7.3 KiB
C
262 lines
7.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_GENERIC_BUG_H
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#define _ASM_GENERIC_BUG_H
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#include <linux/compiler.h>
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#include <linux/instrumentation.h>
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#define CUT_HERE "------------[ cut here ]------------\n"
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#ifdef CONFIG_GENERIC_BUG
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#define BUGFLAG_WARNING (1 << 0)
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#define BUGFLAG_ONCE (1 << 1)
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#define BUGFLAG_DONE (1 << 2)
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#define BUGFLAG_NO_CUT_HERE (1 << 3) /* CUT_HERE already sent */
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#define BUGFLAG_TAINT(taint) ((taint) << 8)
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#define BUG_GET_TAINT(bug) ((bug)->flags >> 8)
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#endif
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#ifndef __ASSEMBLY__
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#include <linux/kernel.h>
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#ifdef CONFIG_BUG
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#ifdef CONFIG_GENERIC_BUG
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struct bug_entry {
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#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
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unsigned long bug_addr;
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#else
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signed int bug_addr_disp;
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#endif
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#ifdef CONFIG_DEBUG_BUGVERBOSE
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#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
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const char *file;
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#else
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signed int file_disp;
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#endif
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unsigned short line;
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#endif
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unsigned short flags;
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};
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#endif /* CONFIG_GENERIC_BUG */
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/*
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* Don't use BUG() or BUG_ON() unless there's really no way out; one
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* example might be detecting data structure corruption in the middle
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* of an operation that can't be backed out of. If the (sub)system
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* can somehow continue operating, perhaps with reduced functionality,
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* it's probably not BUG-worthy.
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*
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* If you're tempted to BUG(), think again: is completely giving up
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* really the *only* solution? There are usually better options, where
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* users don't need to reboot ASAP and can mostly shut down cleanly.
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*/
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#ifndef HAVE_ARCH_BUG
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#define BUG() do { \
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printk("BUG: failure at %s:%d/%s()!\n", __FILE__, __LINE__, __func__); \
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barrier_before_unreachable(); \
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panic("BUG!"); \
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} while (0)
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#endif
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#ifndef HAVE_ARCH_BUG_ON
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#define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while (0)
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#endif
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/*
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* WARN(), WARN_ON(), WARN_ON_ONCE, and so on can be used to report
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* significant kernel issues that need prompt attention if they should ever
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* appear at runtime.
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*
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* Do not use these macros when checking for invalid external inputs
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* (e.g. invalid system call arguments, or invalid data coming from
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* network/devices), and on transient conditions like ENOMEM or EAGAIN.
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* These macros should be used for recoverable kernel issues only.
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* For invalid external inputs, transient conditions, etc use
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* pr_err[_once/_ratelimited]() followed by dump_stack(), if necessary.
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* Do not include "BUG"/"WARNING" in format strings manually to make these
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* conditions distinguishable from kernel issues.
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*
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* Use the versions with printk format strings to provide better diagnostics.
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*/
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#ifndef __WARN_FLAGS
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extern __printf(4, 5)
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void warn_slowpath_fmt(const char *file, const int line, unsigned taint,
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const char *fmt, ...);
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#define __WARN() __WARN_printf(TAINT_WARN, NULL)
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#define __WARN_printf(taint, arg...) do { \
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instrumentation_begin(); \
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warn_slowpath_fmt(__FILE__, __LINE__, taint, arg); \
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instrumentation_end(); \
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} while (0)
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#else
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extern __printf(1, 2) void __warn_printk(const char *fmt, ...);
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#define __WARN() __WARN_FLAGS(BUGFLAG_TAINT(TAINT_WARN))
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#define __WARN_printf(taint, arg...) do { \
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instrumentation_begin(); \
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__warn_printk(arg); \
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__WARN_FLAGS(BUGFLAG_NO_CUT_HERE | BUGFLAG_TAINT(taint));\
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instrumentation_end(); \
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} while (0)
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#define WARN_ON_ONCE(condition) ({ \
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int __ret_warn_on = !!(condition); \
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if (unlikely(__ret_warn_on)) \
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__WARN_FLAGS(BUGFLAG_ONCE | \
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BUGFLAG_TAINT(TAINT_WARN)); \
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unlikely(__ret_warn_on); \
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})
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#endif
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/* used internally by panic.c */
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struct warn_args;
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struct pt_regs;
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void __warn(const char *file, int line, void *caller, unsigned taint,
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struct pt_regs *regs, struct warn_args *args);
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#ifndef WARN_ON
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#define WARN_ON(condition) ({ \
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int __ret_warn_on = !!(condition); \
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if (unlikely(__ret_warn_on)) \
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__WARN(); \
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unlikely(__ret_warn_on); \
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})
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#endif
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#ifndef WARN
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#define WARN(condition, format...) ({ \
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int __ret_warn_on = !!(condition); \
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if (unlikely(__ret_warn_on)) \
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__WARN_printf(TAINT_WARN, format); \
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unlikely(__ret_warn_on); \
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})
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#endif
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#define WARN_TAINT(condition, taint, format...) ({ \
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int __ret_warn_on = !!(condition); \
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if (unlikely(__ret_warn_on)) \
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__WARN_printf(taint, format); \
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unlikely(__ret_warn_on); \
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})
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#ifndef WARN_ON_ONCE
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#define WARN_ON_ONCE(condition) ({ \
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static bool __section(".data.once") __warned; \
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int __ret_warn_once = !!(condition); \
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\
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if (unlikely(__ret_warn_once && !__warned)) { \
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__warned = true; \
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WARN_ON(1); \
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} \
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unlikely(__ret_warn_once); \
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})
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#endif
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#define WARN_ONCE(condition, format...) ({ \
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static bool __section(".data.once") __warned; \
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int __ret_warn_once = !!(condition); \
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\
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if (unlikely(__ret_warn_once && !__warned)) { \
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__warned = true; \
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WARN(1, format); \
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} \
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unlikely(__ret_warn_once); \
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})
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#define WARN_TAINT_ONCE(condition, taint, format...) ({ \
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static bool __section(".data.once") __warned; \
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int __ret_warn_once = !!(condition); \
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\
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if (unlikely(__ret_warn_once && !__warned)) { \
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__warned = true; \
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WARN_TAINT(1, taint, format); \
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} \
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unlikely(__ret_warn_once); \
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})
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#else /* !CONFIG_BUG */
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#ifndef HAVE_ARCH_BUG
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#define BUG() do {} while (1)
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#endif
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#ifndef HAVE_ARCH_BUG_ON
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#define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while (0)
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#endif
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#ifndef HAVE_ARCH_WARN_ON
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#define WARN_ON(condition) ({ \
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int __ret_warn_on = !!(condition); \
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unlikely(__ret_warn_on); \
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})
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#endif
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#ifndef WARN
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#define WARN(condition, format...) ({ \
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int __ret_warn_on = !!(condition); \
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no_printk(format); \
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unlikely(__ret_warn_on); \
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})
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#endif
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#define WARN_ON_ONCE(condition) WARN_ON(condition)
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#define WARN_ONCE(condition, format...) WARN(condition, format)
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#define WARN_TAINT(condition, taint, format...) WARN(condition, format)
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#define WARN_TAINT_ONCE(condition, taint, format...) WARN(condition, format)
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#endif
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/*
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* WARN_ON_SMP() is for cases that the warning is either
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* meaningless for !SMP or may even cause failures.
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* It can also be used with values that are only defined
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* on SMP:
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*
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* struct foo {
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* [...]
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* #ifdef CONFIG_SMP
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* int bar;
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* #endif
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* };
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*
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* void func(struct foo *zoot)
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* {
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* WARN_ON_SMP(!zoot->bar);
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*
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* For CONFIG_SMP, WARN_ON_SMP() should act the same as WARN_ON(),
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* and should be a nop and return false for uniprocessor.
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*
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* if (WARN_ON_SMP(x)) returns true only when CONFIG_SMP is set
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* and x is true.
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*/
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#ifdef CONFIG_SMP
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# define WARN_ON_SMP(x) WARN_ON(x)
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#else
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/*
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* Use of ({0;}) because WARN_ON_SMP(x) may be used either as
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* a stand alone line statement or as a condition in an if ()
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* statement.
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* A simple "0" would cause gcc to give a "statement has no effect"
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* warning.
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*/
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# define WARN_ON_SMP(x) ({0;})
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#endif
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/*
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* WARN_ON_FUNCTION_MISMATCH() warns if a value doesn't match a
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* function address, and can be useful for catching issues with
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* callback functions, for example.
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*
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* With CONFIG_CFI_CLANG, the warning is disabled because the
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* compiler replaces function addresses taken in C code with
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* local jump table addresses, which breaks cross-module function
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* address equality.
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*/
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#if defined(CONFIG_CFI_CLANG) && defined(CONFIG_MODULES)
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# define WARN_ON_FUNCTION_MISMATCH(x, fn) ({ 0; })
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#else
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# define WARN_ON_FUNCTION_MISMATCH(x, fn) WARN_ON_ONCE((x) != (fn))
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#endif
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#endif /* __ASSEMBLY__ */
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#endif
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