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Date:   Wed, 28 Sep 2022 10:13:12 -0700
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>,
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        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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Subject: Re: [PATCH v2 01/16] slab: Remove __malloc attribute from realloc
 functions
Message-ID: <202209281011.66DD717D@keescook>
References: <20220923202822.2667581-1-keescook@chromium.org>
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 <CAMuHMdXK+UN1YVZm9DenuXAM8hZRUZJwp=SXsueP7sWiVU3a9A@mail.gmail.com>
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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