linux-kernel - Re: [PATCH -tip] kasan: Emit different calls for instrumentable memintrinsics

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Date:   Thu, 9 Feb 2023 23:43:05 +0100
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Marco Elver <elver@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-kbuild@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Tony Lindgren <tony@...mide.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH -tip] kasan: Emit different calls for instrumentable memintrinsics

On Wed, Feb 8, 2023 at 7:42 PM Marco Elver <elver@...gle.com> wrote:
>
> Clang 15 will provide an option to prefix calls to memcpy/memset/memmove
> with __asan_ in instrumented functions: https://reviews.llvm.org/D122724

Hi Marco,

Does this option affect all functions or only the ones that are marked
with no_sanitize?

Based on the LLVM patch description, should we also change the normal
memcpy/memset/memmove to be noninstrumented?

These __asan_mem* functions are not defined in the kernel AFAICS.
Should we add them?

Or maybe we should just use "__" as the prefix, as right now __mem*
functions are the ones that are not instrumented?

Thanks!

> GCC does not yet have similar support.
>
> Use it to regain KASAN instrumentation of memcpy/memset/memmove on
> architectures that require noinstr to be really free from instrumented
> mem*() functions (all GENERIC_ENTRY architectures).
>
> Fixes: 69d4c0d32186 ("entry, kasan, x86: Disallow overriding mem*() functions")
> Signed-off-by: Marco Elver <elver@...gle.com>
> ---
>
> The Fixes tag is just there to show the dependency, and that people
> shouldn't apply this patch without 69d4c0d32186.
>
> ---
>  scripts/Makefile.kasan | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
> index b9e94c5e7097..78336b04c077 100644
> --- a/scripts/Makefile.kasan
> +++ b/scripts/Makefile.kasan
> @@ -38,6 +38,13 @@ endif
>
>  CFLAGS_KASAN += $(call cc-param,asan-stack=$(stack_enable))
>
> +ifdef CONFIG_GENERIC_ENTRY
> +# Instrument memcpy/memset/memmove calls by using instrumented __asan_mem*()
> +# instead. With compilers that don't support this option, compiler-inserted
> +# memintrinsics won't be checked by KASAN.
> +CFLAGS_KASAN += $(call cc-param,asan-kernel-mem-intrinsic-prefix)
> +endif
> +
>  endif # CONFIG_KASAN_GENERIC
>
>  ifdef CONFIG_KASAN_SW_TAGS
> --
> 2.39.1.519.gcb327c4b5f-goog
>