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

[Guenter Roeck]

On 2/2/22 14:11, Kees Cook wrote:
> On Wed, Feb 02, 2022 at 08:09:03AM -0800, Guenter Roeck wrote:
> > On Wed, Aug 18, 2021 at 01:11:17AM -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 a4aca01a4835..af22b83cede7 100644
> > > --- a/Makefile
> > > +++ b/Makefile
> > > @@ -1072,7 +1072,6 @@ 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 += -Wno-array-bounds
> > >   KBUILD_CFLAGS += $(call cc-disable-warning, stringop-overflow)
> > >   
> > >   # Another good warning that we'll want to enable eventually
> >
> > alpha:defconfig:
> >
> > 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);
>
> Ah! With Arnd and Nathan's help, I saw:
> https://lore.kernel.org/all/20210912160149.2227137-3-linux@xxxxxxxxxxxx/

Guilty as charged. Sorry, I didn't try to analyze the problem,
or I might have noticed (and saved you some work).

Guenter

> which is solving the same problem (just manifested through different
> diagnostics). The same solution works here. I'll get the patches sent...