linux-hardening - Re: [PATCH v3 2/8] Compiler Attributes: add __alloc

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Date:   Fri, 1 Oct 2021 00:48:53 +0200
From:   Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Andy Whitcroft <apw@...onical.com>,
        Christoph Lameter <cl@...ux.com>,
        Daniel Micay <danielmicay@...il.com>,
        David Rientjes <rientjes@...gle.com>,
        Dennis Zhou <dennis@...nel.org>,
        Dwaipayan Ray <dwaipayanray1@...il.com>,
        Joe Perches <joe@...ches.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        Pekka Enberg <penberg@...nel.org>, Tejun Heo <tj@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Miguel Ojeda <ojeda@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Linux-MM <linux-mm@...ck.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3 2/8] Compiler Attributes: add __alloc_size() for better
 bounds checking

On Fri, Oct 1, 2021 at 12:27 AM Kees Cook <keescook@...omium.org> wrote:
>
> +ifdef CONFIG_CC_IS_GCC
> +# The allocators already balk at large sizes, so silence the compiler
> +# warnings for bounds checks involving those possible values. While
> +# -Wno-alloc-size-larger-than would normally be used here, earlier versions
> +# of gcc (<9.1) weirdly don't handle the option correctly when _other_
> +# warnings are produced (?!). Using -Walloc-size-larger-than=SIZE_MAX
> +# doesn't work (as it is documented to), silently resolving to "0" prior to
> +# version 9.1 (and producing an error more recently). Numeric values larger
> +# than PTRDIFF_MAX also don't work prior to version 9.1, which are silently
> +# ignored, continuing to default to PTRDIFF_MAX. So, left with no other
> +# choice, we must perform a versioned check to disable this warning.
> +# https://lore.kernel.org/lkml/20210824115859.187f272f@canb.auug.org.au
> +KBUILD_CFLAGS += $(call cc-ifversion, -ge, 0901, -Wno-alloc-size-larger-than)
> +endif

An amazing journey!

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

Cheers,
Miguel