linux-kernel - Re: [PATCH v2] string: use __builtin

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Message-ID: <CAG_fn=U67cq4502h2G8kms8r6e=13tn8Ta+QWhA8N6cK-PFyaA@mail.gmail.com>
Date:   Tue, 30 May 2023 10:40:26 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     glider@...gle.com, andy@...nel.org, akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, elver@...gle.com,
        dvyukov@...gle.com, kasan-dev@...glegroups.com,
        ndesaulniers@...gle.com, nathan@...nel.org, keescook@...omium.org
Subject: Re: [PATCH v2] string: use __builtin_memcpy() in strlcpy/strlcat

On Tue, May 30, 2023 at 10:39 AM Alexander Potapenko <glider@...gle.com> wrote:
>
> lib/string.c is built with -ffreestanding, which prevents the compiler
> from replacing certain functions with calls to their library versions.
>
> On the other hand, this also prevents Clang and GCC from instrumenting
> calls to memcpy() when building with KASAN, KCSAN or KMSAN:
>  - KASAN normally replaces memcpy() with __asan_memcpy() with the
>    additional cc-param,asan-kernel-mem-intrinsic-prefix=1;
>  - KCSAN and KMSAN replace memcpy() with __tsan_memcpy() and
>    __msan_memcpy() by default.
>
> To let the tools catch memory accesses from strlcpy/strlcat, replace
> the calls to memcpy() with __builtin_memcpy(), which KASAN, KCSAN and
> KMSAN are able to replace even in -ffreestanding mode.
>
> This preserves the behavior in normal builds (__builtin_memcpy() ends up
> being replaced with memcpy()), and does not introduce new instrumentation
> in unwanted places, as strlcpy/strlcat are already instrumented.
>
> Suggested-by: Marco Elver <elver@...gle.com>
> Signed-off-by: Alexander Potapenko <glider@...gle.com>
> Link: https://lore.kernel.org/all/20230224085942.1791837-1-elver@google.com/

Sorry, missed a "Reviewed-by: Marco Elver <elver@...gle.com>" from the
previous thread:
https://lore.kernel.org/lkml/CAG_fn=UzQ-jnQrxzvLE6EV37zSVCOGPmsVTxyfp1wXzBir4vAg@mail.gmail.com/T/


> Acked-by: Kees Cook <keescook@...omium.org>