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In-Reply-To: <032386fc-fffb-1f17-8cfd-94b35b6947ee@I-love.SAKURA.ne.jp>
From:   Alexander Potapenko <glider@google.com>
Date:   Wed, 1 Mar 2023 14:41:06 +0100
Message-ID: <CAG_fn=V4-zzo+6HFG+wCbJRYHRh+Xx=r1weyCBJG-afpaG4Hag@mail.gmail.com>
Subject: Re: [PATCH] fbcon: Use kzalloc() in fbcon_prepare_logo()
To:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc:     Geert Uytterhoeven <geert@linux-m68k.org>,
        Marco Elver <elver@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Helge Deller <deller@gmx.de>,
        Linux Fbdev development list <linux-fbdev@vger.kernel.org>,
        DRI <dri-devel@lists.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>
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>
> I'd like to avoid touching per-arch asm/string.h files if possible.
>
> Can't we do like below (i.e. keep asm implementations as-is, but
> automatically redirect to __msan_memset()) ? If yes, we could move all
> __msan_*() redirection from per-arch asm/string.h files to the common
> linux/string.h file?
>
> diff --git a/include/linux/string.h b/include/linux/string.h
> index c062c581a98b..403813b04e00 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -360,4 +360,15 @@ static __always_inline size_t str_has_prefix(const char *str, const char *prefix
>         return strncmp(str, prefix, len) == 0 ? len : 0;
>  }
>
> +#if defined(__SANITIZE_MEMORY__) && defined(__NO_FORTIFY)
> +#undef memset
> +#define memset(dest, src, count) __msan_memset((dest), (src), (count))
> +#undef memset16
> +#define memset16(dest, src, count) __msan_memset((dest), (src), (count) << 1)
> +#undef memset32
> +#define memset32(dest, src, count) __msan_memset((dest), (src), (count) << 2)
> +#undef memset64
> +#define memset64(dest, src, count) __msan_memset((dest), (src), (count) << 3)
> +#endif

The problem with this approach is that it can only work for
memset/memcpy/memmove, whereas any function that is implemented in
lib/string.c may require undefining the respective __HAVE_ARCH_FNAME
so that KMSAN can instrument it.