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.
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
Documentation/dev-tools/kasan.rst | 27 +++++++++++++--------------
1 file changed, 13 insertions(+), 14 deletions(-)
diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
index 2f939241349d..1fb4b715a3ce 100644
--- a/Documentation/dev-tools/kasan.rst
+++ b/Documentation/dev-tools/kasan.rst
@@ -200,12 +200,11 @@ 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.
@@ -214,23 +213,23 @@ 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
--
2.31.0.rc2.261.g7f71774620-goog
