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

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

[Kees Cook]

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@arndb.de>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: linux-kbuild@vger.kernel.org
Co-developed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.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)
 
 # Another good warning that we'll want to enable eventually
-- 
2.30.2

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

[Guenter Roeck]

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@arndb.de>
> Cc: Masahiro Yamada <masahiroy@kernel.org>
> Cc: linux-kbuild@vger.kernel.org
> Co-developed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> Signed-off-by: Kees Cook <keescook@chromium.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

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

[Kees Cook]

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@arndb.de>
> > Cc: Masahiro Yamada <masahiroy@kernel.org>
> > Cc: linux-kbuild@vger.kernel.org
> > Co-developed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> > Signed-off-by: Kees Cook <keescook@chromium.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?

Looks like GCC isn't happy about an unsigned long->void * conversion
here...

include/asm/page.h:#define PAGE_OFFSET          0xfffffc0000000000UL
...
include/uapi/asm/setup.h:#define KERNEL_START_PHYS      0x1000000 /* required: Wildfire/Titan/Marvel */
include/uapi/asm/setup.h:#define EMPTY_PGT (PAGE_OFFSET+KERNEL_START_PHYS+0x04000)
...
mm/init.c:      memset((void *) EMPTY_PGT, 0, PAGE_SIZE);

I'll try to figure out the right annotations to fix this...

-- 
Kees Cook

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

[Guenter Roeck]

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@arndb.de>
>>> Cc: Masahiro Yamada <masahiroy@kernel.org>
>>> Cc: linux-kbuild@vger.kernel.org
>>> Co-developed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
>>> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
>>> Signed-off-by: Kees Cook <keescook@chromium.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

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

[Kees Cook]

On Tue, Aug 31, 2021 at 12:40:53PM -0700, Guenter Roeck wrote:
> 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.

Ah! Yes, heh. That would be my problem; I've got 10.3 for my builders.
Thanks! I will give 11.2 a spin.

-- 
Kees Cook

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

[Guenter Roeck]

On 8/31/21 1:18 PM, Kees Cook wrote:
> On Tue, Aug 31, 2021 at 12:40:53PM -0700, Guenter Roeck wrote:
>> 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.
> 
> Ah! Yes, heh. That would be my problem; I've got 10.3 for my builders.
> Thanks! I will give 11.2 a spin.
> 
In case you don't have gcc 11.2 available - I tested with 11.1 as well;
that also fails.

Guenter

[PATCH v3 5/5] Makefile: Enable -Wzero-length-bounds

[Kees Cook]

With all known internal zero-length accesses fixed, it is possible to
enable -Wzero-length-bounds globally. Since this is included by default
in -Warray-bounds, we just need to stop disabling it.

Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: linux-kbuild@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 Makefile | 1 -
 1 file changed, 1 deletion(-)

diff --git a/Makefile b/Makefile
index 8e7e73a642e2..8e732e875e78 100644
--- a/Makefile
+++ b/Makefile
@@ -994,7 +994,6 @@ KBUILD_CFLAGS += -Wno-pointer-sign
 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, stringop-overflow)
 
 # Another good warning that we'll want to enable eventually
-- 
2.30.2