linux-hardening - Re: [PATCH v3 4/5] Makefile: Enable -Warray-bounds

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Date:   Mon, 30 Aug 2021 21:31:28 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Masahiro Yamada <masahiroy@...nel.org>,
        linux-kbuild@...r.kernel.org,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Keith Packard <keithp@...thp.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        clang-built-linux@...glegroups.com, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3 4/5] Makefile: Enable -Warray-bounds

On Fri, Aug 27, 2021 at 09:30:14AM -0700, Kees Cook wrote:
> With the recent fixes for flexible arrays and expanded FORTIFY_SOURCE
> coverage, it is now possible to enable -Warray-bounds. Since both
> GCC and Clang include -Warray-bounds in -Wall, we just need to stop
> disabling it.
> 
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Masahiro Yamada <masahiroy@...nel.org>
> Cc: linux-kbuild@...r.kernel.org
> Co-developed-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  Makefile | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/Makefile b/Makefile
> index e4f5895badb5..8e7e73a642e2 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -995,7 +995,6 @@ KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)
>  
>  # We'll want to enable this eventually, but it's not going away for 5.7 at least
>  KBUILD_CFLAGS += $(call cc-disable-warning, zero-length-bounds)
> -KBUILD_CFLAGS += $(call cc-disable-warning, array-bounds)
>  KBUILD_CFLAGS += $(call cc-disable-warning, stringop-overflow)
>  

This patch causes 'alpha' builds to fail when trying to build an image with
gcc 11.2.

In file included from include/linux/string.h:20,
                 from include/linux/bitmap.h:11,
                 from include/linux/cpumask.h:12,
                 from include/linux/smp.h:13,
                 from include/linux/lockdep.h:14,
                 from include/linux/spinlock.h:63,
                 from include/linux/mmzone.h:8,
                 from include/linux/gfp.h:6,
                 from include/linux/mm.h:10,
                 from include/linux/pagemap.h:8,
                 from arch/alpha/mm/init.c:10:
In function '__memset',
    inlined from '__bad_pagetable' at arch/alpha/mm/init.c:79:2:
arch/alpha/include/asm/string.h:37:32: error: '__builtin_memset' offset [0, 8191] is out of the bounds [0, 0] [-Werror=array-bounds]
   37 |                         return __builtin_memset(s, c, n);
      |                                ^~~~~~~~~~~~~~~~~~~~~~~~~
In function '__memset',
    inlined from '__bad_page' at arch/alpha/mm/init.c:86:2:
arch/alpha/include/asm/string.h:37:32: error: '__builtin_memset' offset [0, 8191] is out of the bounds [0, 0] [-Werror=array-bounds]
   37 |                         return __builtin_memset(s, c, n);
      |                                ^~~~~~~~~~~~~~~~~~~~~~~~~
In function '__memset',
    inlined from 'paging_init' at arch/alpha/mm/init.c:256:2:
arch/alpha/include/asm/string.h:37:32: error: '__builtin_memset' offset [0, 8191] is out of the bounds [0, 0] [-Werror=array-bounds]
   37 |                         return __builtin_memset(s, c, n);

Seen in next-20210830.

Guenter