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Date:   Fri, 12 Mar 2021 16:07:25 +0100
From:   Marco Elver <elver@google.com>
To:     Andrey Konovalov <andreyknvl@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Alexander Potapenko <glider@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Dmitry Vyukov <dvyukov@google.com>, kasan-dev@googlegroups.com,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 02/11] kasan: docs: update overview section
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References: <c2bbb56eaea80ad484f0ee85bb71959a3a63f1d7.1615559068.git.andreyknvl@google.com>
 <1486fba8514de3d7db2f47df2192db59228b0a7b.1615559068.git.andreyknvl@google.com>
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On Fri, Mar 12, 2021 at 03:24PM +0100, Andrey Konovalov wrote:
> 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.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

Reviewed-by: Marco Elver <elver@google.com>

> ---
> 
> Changes v1->v2:
> - Mention GCC support for HW_TAGS.
> ---
>  Documentation/dev-tools/kasan.rst | 27 +++++++++++++++++++--------
>  1 file changed, 19 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/dev-tools/kasan.rst b/Documentation/dev-tools/kasan.rst
> index b3b2c517db55..2f2697b290d5 100644
> --- a/Documentation/dev-tools/kasan.rst
> +++ b/Documentation/dev-tools/kasan.rst
> @@ -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,
> -- 
> 2.31.0.rc2.261.g7f71774620-goog
>