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From:   Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Date:   Thu, 19 Aug 2021 02:04:46 +0200
Message-ID: <CANiq72krkjtmwwZOebbVnPismTPoe2y+vCXuOXbBwE=1-BS2hg@mail.gmail.com>
Subject: Re: [PATCH v2 1/7] Compiler Attributes: Add __alloc_size() for better
 bounds checking
To:     Kees Cook <keescook@chromium.org>
Cc:     linux-kernel <linux-kernel@vger.kernel.org>,
        Miguel Ojeda <ojeda@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Joe Perches <joe@perches.com>,
        Andy Whitcroft <apw@canonical.com>,
        Dwaipayan Ray <dwaipayanray1@gmail.com>,
        Lukas Bulwahn <lukas.bulwahn@gmail.com>,
        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>,
        Vlastimil Babka <vbabka@suse.cz>,
        Daniel Micay <danielmicay@gmail.com>,
        Dennis Zhou <dennis@kernel.org>, Tejun Heo <tj@kernel.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
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On Wed, Aug 18, 2021 at 11:40 PM Kees Cook <keescook@chromium.org> wrote:
>
> GCC and Clang can use the "alloc_size" attribute to better inform the
> results of __builtin_object_size() (for compile-time constant values).
> Clang can additionally use alloc_size to inform the results of
> __builtin_dynamic_object_size() (for run-time values).
>
> Because GCC sees the frequent use of struct_size() as an allocator size
> argument, and notices it can return SIZE_MAX (the overflow indication),
> it complains about these call sites may overflow (since SIZE_MAX is
> greater than the default -Walloc-size-larger-than=PTRDIFF_MAX). This
> isn't helpful since we already know a SIZE_MAX will be caught at run-time
> (this was an intentional design). Instead, just disable this check as
> it is both a false positive and redundant. (Clang does not have this
> warning option.)

Thanks!

Reviewed-by: Miguel Ojeda <ojeda@kernel.org>

Cheers,
Miguel