linux-kernel - Re: [PATCH] amdgpu_dm: fix nonblocking atomic commit use-after-free

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Date:   Fri, 24 Jul 2020 10:33:49 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Paul Menzel <pmenzel@...gen.mpg.de>
Cc:     Mazin Rezk <mnrzk@...tonmail.com>, linux-kernel@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christian König <christian.koenig@....com>,
        Harry Wentland <Harry.Wentland@....com>,
        Nicholas Kazlauskas <nicholas.kazlauskas@....com>,
        sunpeng.li@....com, Alexander Deucher <Alexander.Deucher@....com>,
        1i5t5.duncan@....net, mphantomx@...oo.com.br,
        regressions@...mhuis.info, anthony.ruhier@...il.com
Subject: Re: [PATCH] amdgpu_dm: fix nonblocking atomic commit use-after-free

On Fri, Jul 24, 2020 at 09:45:18AM +0200, Paul Menzel wrote:
> Am 24.07.20 um 00:32 schrieb Kees Cook:
> > On Thu, Jul 23, 2020 at 09:10:15PM +0000, Mazin Rezk wrote:
> As Linux 5.8-rc7 is going to be released this Sunday, I wonder, if commit
> 3202fa62f ("slub: relocate freelist pointer to middle of object") should be
> reverted for now to fix the regression for the users according to Linux’ no
> regression policy. Once the AMDGPU/DRM driver issue is fixed, it can be
> reapplied. I know it’s not optimal, but as some testing is going to be
> involved for the fix, I’d argue it’s the best option for the users.

Well, the SLUB defense was already released in v5.7, so I'm not sure it
really helps for amdgpu_dm users seeing it there too. There was a fix to
disable the async path for this driver that worked around the bug too,
yes? That seems like a safer and more focused change that doesn't revert
the SLUB defense for all users, and would actually provide a complete,
I think, workaround whereas reverting the SLUB change means the race
still exists. For example, it would be hit with slab poisoning, etc.

-- 
Kees Cook