linux-kernel - Re: [PATCH v2 6/7] percpu: Add __alloc_size attributes for better bounds checking

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Message-ID: <202108192221.396DFDC9@keescook>
Date:   Thu, 19 Aug 2021 22:27:26 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, Daniel Micay <danielmicay@...il.com>,
        Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>, linux-mm@...ck.org,
        Joe Perches <joe@...ches.com>, Miguel Ojeda <ojeda@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Andy Whitcroft <apw@...onical.com>,
        Dwaipayan Ray <dwaipayanray1@...il.com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        clang-built-linux@...glegroups.com, linux-kbuild@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 6/7] percpu: Add __alloc_size attributes for better
 bounds checking

On Thu, Aug 19, 2021 at 10:11:15PM -0700, Andrew Morton wrote:
> On Wed, 18 Aug 2021 14:40:20 -0700 Kees Cook <keescook@...omium.org> wrote:
> 
> > As already done in GrapheneOS, add the __alloc_size attribute for
> > appropriate percpu allocator interfaces, to provide additional hinting
> > for better bounds checking, assisting CONFIG_FORTIFY_SOURCE and other
> > compiler optimizations.
> > 
> 
> Caught one, I assume:
> 
> In file included from ./include/linux/string.h:262,
>                  from ./include/linux/bitmap.h:11,
>                  from ./include/linux/cpumask.h:12,
>                  from ./arch/x86/include/asm/cpumask.h:5,
>                  from ./arch/x86/include/asm/msr.h:11,
>                  from ./arch/x86/include/asm/processor.h:22,
>                  from ./arch/x86/include/asm/cpufeature.h:5,
>                  from ./arch/x86/include/asm/thread_info.h:53,
>                  from ./include/linux/thread_info.h:60,
>                  from ./arch/x86/include/asm/preempt.h:7,
>                  from ./include/linux/preempt.h:78,
>                  from ./include/linux/spinlock.h:55,
>                  from ./include/linux/mmzone.h:8,
>                  from ./include/linux/gfp.h:6,
>                  from ./include/linux/slab.h:15,
>                  from drivers/misc/lkdtm/heap.c:7:
> In function 'memset',
>     inlined from 'lkdtm_VMALLOC_LINEAR_OVERFLOW' at drivers/misc/lkdtm/heap.c:27:2:
> ./include/linux/fortify-string.h:172:3: error: call to '__write_overflow' declared with attribute error: detected write beyond size of object passed as 1st parameter
>   172 |   __write_overflow();
>       |   ^~~~~~~~~~~~~~~~~~
> make[3]: *** [drivers/misc/lkdtm/heap.o] Error 1
> make[2]: *** [drivers/misc/lkdtm] Error 2
> make[1]: *** [drivers/misc] Error 2
> make: *** [drivers] Error 2
> 
> I want to get a kernel release out, so I'll hide
> mm-vmalloc-add-__alloc_size-attributes-for-better-bounds-checking.patch
> for now.

In the cover letter[1], I listed the needed fixes that were sent
separately from this series. Quoting here:

> To build without warnings, this series needs a couple small fixes for
> allmodconfig, which I sent separately:
> https://lore.kernel.org/lkml/20210818174855.2307828-5-keescook@chromium.org/
> https://lore.kernel.org/lkml/20210818044252.1533634-1-keescook@chromium.org/
> https://lore.kernel.org/lkml/20210818043912.1466447-1-keescook@chromium.org/

What you hit is the first one, which is already in Greg's tree:
https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git/commit/?h=char-misc-next&id=e6d468d32cd084edd030a8bae76440b17b854b5c

The other two have also been taken:
https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git/commit/?h=staging-next&id=cbe34165cc1b7d1110b268ba8b9f30843c941639
https://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git/commit/?id=a31e5a4158d03595ca4258b94397d4097be0ebe4

-Kees

[1] https://lore.kernel.org/lkml/20210818214021.2476230-1-keescook@chromium.org/

-- 
Kees Cook