From: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Subject: 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@xxxxxxxxxx Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Reviewed-by: Marco Elver <elver@xxxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Documentation/dev-tools/kasan.rst | 27 +++++++++++++++++++-------- 1 file changed, 19 insertions(+), 8 deletions(-) --- a/Documentation/dev-tools/kasan.rst~kasan-docs-update-overview-section +++ a/Documentation/dev-tools/kasan.rst @@ -11,17 +11,31 @@ designed to find out-of-bound and use-af 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. + +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+. -Currently generic KASAN is supported for the x86_64, arm, arm64, xtensa, s390 +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 cho 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, _
