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authorAndrey Konovalov <andreyknvl@google.com>2021-04-29 23:00:27 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-04-30 11:20:42 -0700
commitb8191d7d57e86eda934ef82081c294e6a184b000 (patch)
tree7ec1f82384de630c610c9c1428ee3b28302a118f /Documentation/dev-tools
parentf359074768bf406b64d62560e88ff9820b600220 (diff)
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.rst27
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