linux-kernel - Re: [PATCH -tip v3] kasan: Emit different calls for instrumentable memintrinsics

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Message-ID: <Y+tf5ZOR5J92wSsw@hirez.programming.kicks-ass.net>
Date:   Tue, 14 Feb 2023 11:18:13 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Marco Elver <elver@...gle.com>
Cc:     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>,
        Andrey Konovalov <andreyknvl@...il.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>,
        Jakub Jelinek <jakub@...hat.com>,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH -tip v3] kasan: Emit different calls for instrumentable
 memintrinsics

On Mon, Feb 13, 2023 at 09:13:35PM +0100, Marco Elver wrote:
> Clang 15 will provide an option to prefix calls to memcpy/memset/memmove
> with __asan_ in instrumented functions: https://reviews.llvm.org/D122724
> 
> GCC will add support in future:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108777
> 
> 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>

Thanks!

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

> ---
> v3:
> * Resend with actual fix.
> 
> v2:
> * Use asan-kernel-mem-intrinsic-prefix=1, so that once GCC supports the
>   param, it also works there (it needs the =1).
> 
> 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..3b35a88af60d 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=1)
> +endif
> +
>  endif # CONFIG_KASAN_GENERIC
>  
>  ifdef CONFIG_KASAN_SW_TAGS
> -- 
> 2.39.1.581.gbfd45094c4-goog
>