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Date:   Wed, 28 Sep 2022 23:39:06 +0200
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Subject: Re: [PATCH v2 01/16] slab: Remove __malloc attribute from realloc
 functions
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To:     Kees Cook <keescook@chromium.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     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>,
        =?UTF-8?Q?Christian_K=c3=b6nig?= <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
References: <20220923202822.2667581-1-keescook@chromium.org>
 <20220923202822.2667581-2-keescook@chromium.org>
 <CAMuHMdXK+UN1YVZm9DenuXAM8hZRUZJwp=SXsueP7sWiVU3a9A@mail.gmail.com>
 <202209281011.66DD717D@keescook>
From:   Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <202209281011.66DD717D@keescook>
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On 9/28/22 19:13, Kees Cook wrote:
> 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.

Even in latest next I can see at the end of include/linux/compiler-gcc.h

/*
  * Prior to 9.1, -Wno-alloc-size-larger-than (and therefore the "alloc_size"
  * attribute) do not work, and must be disabled.
  */
#if GCC_VERSION < 90100
#undef __alloc_size__
#endif


> -Kees
>