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@xxxxxxxx>
> > > Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> > > Cc: linux-kbuild@xxxxxxxxxxxxxxx
> > > Co-developed-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> > > Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > > ---
> > >   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