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kasan: docs: update overview section 

Update the "Overview" section in KASAN documentation:

 - Outline main use cases for each mode.

 - Mention that HW_TAGS mode need compiler support too.

 - Move the part about SLUB/SLAB support from "Usage" to "Overview".

 - Punctuation, readability, and other minor clean-ups.

Link: https://lkml.kernel.org/r/1486fba8514de3d7db2f47df2192db59228b0a7b.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>
This commit is contained in:
Andrey Konovalov 2021-04-29 23:00:15 -07:00 committed by Linus Torvalds
parent 96d7d1415a
commit 3cbc37dcdc
1 changed files with 19 additions and 8 deletions
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27
Documentation/dev-tools/kasan.rst
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@ -11,17 +11,31 @@ designed to find out-of-bound and use-after-free bugs. KASAN has three modes:
2. software tag-based KASAN (similar to userspace HWASan),
3. hardware tag-based KASAN (based on hardware memory tagging).
Software KASAN modes (1 and 2) use compile-time instrumentation to insert
validity checks before every memory access, and therefore require a compiler
Generic KASAN is mainly used for debugging due to a large memory overhead.
Software tag-based KASAN can be used for dogfood testing as it has a lower
memory overhead that allows using it with real workloads. Hardware tag-based
KASAN comes with low memory and performance overheads and, therefore, can be
used in production. Either as an in-field memory bug detector or as a security
mitigation.
Software KASAN modes (#1 and #2) use compile-time instrumentation to insert
validity checks before every memory access and, therefore, require a compiler
version that supports that.
Generic KASAN is supported in both GCC and Clang. With GCC it requires version
Generic KASAN is supported in GCC and Clang. With GCC, it requires version
8.3.0 or later. Any supported Clang version is compatible, but detection of
out-of-bounds accesses for global variables is only supported since Clang 11.
Tag-based KASAN is only supported in Clang.
Software tag-based KASAN mode is only supported in Clang.
Currently generic KASAN is supported for the x86_64, arm, arm64, xtensa, s390
The hardware KASAN mode (#3) relies on hardware to perform the checks but
still requires a compiler version that supports memory tagging instructions.
This mode is supported in GCC 10+ and Clang 11+.
Both software KASAN modes work with SLUB and SLAB memory allocators,
while the hardware tag-based KASAN currently only supports SLUB.
Currently, generic KASAN is supported for the x86_64, arm, arm64, xtensa, s390,
and riscv architectures, and tag-based KASAN modes are supported only for arm64.
Usage
@ -39,9 +53,6 @@ For software modes, you also need to choose between CONFIG_KASAN_OUTLINE and
CONFIG_KASAN_INLINE. Outline and inline are compiler instrumentation types.
The former produces smaller binary while the latter is 1.1 - 2 times faster.
Both software KASAN modes work with both SLUB and SLAB memory allocators,
while the hardware tag-based KASAN currently only support SLUB.
For better error reports that include stack traces, enable CONFIG_STACKTRACE.
To augment reports with last allocation and freeing stack of the physical page,