| Message ID | f2f35fdab701f8c709f63d328f98aec2982c8acc.1615559068.git.andreyknvl@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2,01/11] kasan: docs: clean up sections | expand |
On Fri, Mar 12, 2021 at 03:24PM +0100, Andrey Konovalov wrote: > 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@google.com> Reviewed-by: Marco Elver <elver@google.com> > --- > 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 1189be9b4cb5..986410bf269f 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 >
diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst index 1189be9b4cb5..986410bf269f 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
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@google.com> --- Documentation/dev-tools/kasan.rst | 27 +++++++++++++-------------- 1 file changed, 13 insertions(+), 14 deletions(-)