Re: [PATCH v2 01/16] slab: Remove __malloc attribute from realloc functions

From: Kees Cook <keescook@chromium.org>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: "Vlastimil Babka" <vbabka@suse.cz>,
	"Christoph Lameter" <cl@linux.com>,
	"Pekka Enberg" <penberg@kernel.org>,
	"David Rientjes" <rientjes@google.com>,
	"Joonsoo Kim" <iamjoonsoo.kim@lge.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Roman Gushchin" <roman.gushchin@linux.dev>,
	"Hyeonggon Yoo" <42.hyeyoo@gmail.com>,
	"Marco Elver" <elver@google.com>,
	linux-mm@kvack.org, "Ruhl, Michael J" <michael.j.ruhl@intel.com>,
	"David S. Miller" <davem@davemloft.net>,
	"Eric Dumazet" <edumazet@google.com>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Paolo Abeni" <pabeni@redhat.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	"Alex Elder" <elder@kernel.org>,
	"Josef Bacik" <josef@toxicpanda.com>,
	"David Sterba" <dsterba@suse.com>,
	"Sumit Semwal" <sumit.semwal@linaro.org>,
	"Christian König" <christian.koenig@amd.com>,
	"Jesse Brandeburg" <jesse.brandeburg@intel.com>,
	"Daniel Micay" <danielmicay@gmail.com>,
	"Yonghong Song" <yhs@fb.com>, "Miguel Ojeda" <ojeda@kernel.org>,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	linux-btrfs@vger.kernel.org, linux-media@vger.kernel.org,
	dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org,
	linux-fsdevel@vger.kernel.org, intel-wired-lan@lists.osuosl.org,
	dev@openvswitch.org, x86@kernel.org, llvm@lists.linux.dev,
	linux-hardening@vger.kernel.org
Subject: Re: [PATCH v2 01/16] slab: Remove __malloc attribute from realloc functions
Date: Wed, 28 Sep 2022 10:13:12 -0700	[thread overview]
Message-ID: <202209281011.66DD717D@keescook> (raw)
In-Reply-To: <CAMuHMdXK+UN1YVZm9DenuXAM8hZRUZJwp=SXsueP7sWiVU3a9A@mail.gmail.com>

On Wed, Sep 28, 2022 at 09:26:15AM +0200, Geert Uytterhoeven wrote:
> Hi Kees,
> 
> On Fri, Sep 23, 2022 at 10:35 PM Kees Cook <keescook@chromium.org> wrote:
> > The __malloc attribute should not be applied to "realloc" functions, as
> > the returned pointer may alias the storage of the prior pointer. Instead
> > of splitting __malloc from __alloc_size, which would be a huge amount of
> > churn, just create __realloc_size for the few cases where it is needed.
> >
> > Additionally removes the conditional test for __alloc_size__, which is
> > always defined now.
> >
> > Cc: Christoph Lameter <cl@linux.com>
> > Cc: Pekka Enberg <penberg@kernel.org>
> > Cc: David Rientjes <rientjes@google.com>
> > Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Vlastimil Babka <vbabka@suse.cz>
> > Cc: Roman Gushchin <roman.gushchin@linux.dev>
> > Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
> > Cc: Marco Elver <elver@google.com>
> > Cc: linux-mm@kvack.org
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> 
> Thanks for your patch, which is now commit 63caa04ec60583b1 ("slab:
> Remove __malloc attribute from realloc functions") in next-20220927.
> 
> Noreply@ellerman.id.au reported all gcc8-based builds to fail
> (e.g. [1], more at [2]):
> 
>     In file included from <command-line>:
>     ./include/linux/percpu.h: In function ‘__alloc_reserved_percpu’:
>     ././include/linux/compiler_types.h:279:30: error: expected
> declaration specifiers before ‘__alloc_size__’
>      #define __alloc_size(x, ...) __alloc_size__(x, ## __VA_ARGS__) __malloc
>                                   ^~~~~~~~~~~~~~
>     ./include/linux/percpu.h:120:74: note: in expansion of macro ‘__alloc_size’
>     [...]
> 
> It's building fine with e.g. gcc-9 (which is my usual m68k cross-compiler).
> Reverting this commit on next-20220927 fixes the issue.
> 
> [1] http://kisskb.ellerman.id.au/kisskb/buildresult/14803908/
> [2] http://kisskb.ellerman.id.au/kisskb/head/1bd8b75fe6adeaa89d02968bdd811ffe708cf839/

Eek! Thanks for letting me know. I'm confused about this --
__alloc_size__ wasn't optional in compiler_attributes.h -- but obviously
I broke something! I'll go figure this out.

-Kees

-- 
Kees Cook