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

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Date:   Tue, 31 Aug 2021 12:40:53 -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

Hi Kees,

On 8/31/21 10:46 AM, Kees Cook wrote:
> On Mon, Aug 30, 2021 at 09:31:28PM -0700, Guenter Roeck wrote:
>> 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.
> 
> Ah-ha, thanks for the report! I didn't see this in my builds -- what
> config target did you use for this?
> 

The configuration doesn't matter; it fails for me for all configurations,
including defconfig, alllnoconfig, and allmodconfig.
Key is to use gcc 11.2. The image builds just fine with gcc 9.4 and 10.3.

Guenter