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author | Andrey Konovalov <andreyknvl@google.com> | 2021-04-30 08:00:27 +0200 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2021-04-30 20:20:42 +0200 |
commit | b8191d7d57e86eda934ef82081c294e6a184b000 (patch) | |
tree | 7ec1f82384de630c610c9c1428ee3b28302a118f /Documentation/dev-tools | |
parent | kasan: docs: update boot parameters section (diff) | |
download | linux-b8191d7d57e86eda934ef82081c294e6a184b000.tar.xz linux-b8191d7d57e86eda934ef82081c294e6a184b000.zip |
kasan: docs: update GENERIC implementation details section
Update the "Implementation details" section for generic KASAN:
- Don't mention kmemcheck, it's not present in the kernel anymore.
- Don't mention GCC as the only supported compiler.
- Update kasan_mem_to_shadow() definition to match actual code.
- Punctuation, readability, and other minor clean-ups.
Link: https://lkml.kernel.org/r/f2f35fdab701f8c709f63d328f98aec2982c8acc.1615559068.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/dev-tools')
-rw-r--r-- | Documentation/dev-tools/kasan.rst | 27 |
1 files changed, 13 insertions, 14 deletions
diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst index 37af493c7f8e..027878f92291 100644 --- a/Documentation/dev-tools/kasan.rst +++ b/Documentation/dev-tools/kasan.rst @@ -209,12 +209,11 @@ Implementation details Generic KASAN ~~~~~~~~~~~~~ -From a high level perspective, KASAN's approach to memory error detection is -similar to that of kmemcheck: use shadow memory to record whether each byte of -memory is safe to access, and use compile-time instrumentation to insert checks -of shadow memory on each memory access. +Software KASAN modes use shadow memory to record whether each byte of memory is +safe to access and use compile-time instrumentation to insert shadow memory +checks before each memory access. -Generic KASAN dedicates 1/8th of kernel memory to its shadow memory (e.g. 16TB +Generic KASAN dedicates 1/8th of kernel memory to its shadow memory (16TB to cover 128TB on x86_64) and uses direct mapping with a scale and offset to translate a memory address to its corresponding shadow address. @@ -223,23 +222,23 @@ address:: static inline void *kasan_mem_to_shadow(const void *addr) { - return ((unsigned long)addr >> KASAN_SHADOW_SCALE_SHIFT) + return (void *)((unsigned long)addr >> KASAN_SHADOW_SCALE_SHIFT) + KASAN_SHADOW_OFFSET; } where ``KASAN_SHADOW_SCALE_SHIFT = 3``. Compile-time instrumentation is used to insert memory access checks. Compiler -inserts 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 -access is valid or not by checking corresponding shadow memory. +inserts 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 accesses are valid or not by checking corresponding shadow memory. -GCC 5.0 has possibility to perform inline instrumentation. Instead of making -function calls GCC directly inserts the code to check the shadow memory. -This option significantly enlarges kernel but it gives x1.1-x2 performance -boost over outline instrumented kernel. +With inline instrumentation, instead of making function calls, the compiler +directly inserts the code to check shadow memory. This option significantly +enlarges the kernel, but it gives an x1.1-x2 performance boost over the +outline-instrumented kernel. -Generic KASAN is the only mode that delays the reuse of freed object via +Generic KASAN is the only mode that delays the reuse of freed objects via quarantine (see mm/kasan/quarantine.c for implementation). Software tag-based KASAN |