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From: bugzilla-daemon@bugzilla.kernel.org
To: dri-devel@lists.freedesktop.org
Subject: [Bug 207383] [Regression] 5.7 amdgpu/polaris11 gpf: amdgpu_atomic_commit_tail
Date: Tue, 21 Jul 2020 20:56:28 +0000	[thread overview]
Message-ID: <bug-207383-2300-mEGfc6WNe0@https.bugzilla.kernel.org/> (raw)
In-Reply-To: <bug-207383-2300@https.bugzilla.kernel.org/>

https://bugzilla.kernel.org/show_bug.cgi?id=207383

--- Comment #78 from Kees Cook (kees@outflux.net) ---
(In reply to mnrzk from comment #76)
> If my understanding is correct, base would have previously been filled with
> the freelist pointer (since it's the first 8 bytes). Now since the freelist
> pointer is being put in the middle (rounded to the nearest sizeof(void*),
>  or 8 bytes), it's being put in the last 8 bytes of *dm_state
> (or dm_state->context).
> 
> I'll place a void* for padding in the middle of struct dm_atomic_state* and
> if my hypothesis is correct, the padding will be filled with garbage data
> instead of context and the bug should be fixed. Of course, there would
> still be a use-after-free bug in the code which may cause other issues in
> the future so I wouldn't really consider it a solution.

Agreed: that should make it disappear again, but as you say, it's just kicking
the problem down the road since now the failing condition is losing a race with
kfree()+kmalloc()+new contents.

And if you want to detect without crashing, you can just zero the padding at
init time and report when it's non-NULL at workqueue run time... I wonder if
KASAN can run in a mode where the allocation/freeing tracking happens, but
without the heavy checking instrumentation? Then when the corruption is
detected, it could dump a traceback about who did the early kfree()... hmmm.

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  parent reply	other threads:[~2020-07-21 20:56 UTC|newest]

Thread overview: 122+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-21  9:51 [Bug 207383] New: [Regression] 5.7-rc: amdgpu/polaris11 gpf: amdgpu_atomic_commit_tail bugzilla-daemon
2020-04-21  9:57 ` [Bug 207383] " bugzilla-daemon
2020-04-21 10:04 ` bugzilla-daemon
2020-04-23  4:59 ` bugzilla-daemon
2020-04-27 19:24 ` bugzilla-daemon
2020-04-27 19:42 ` bugzilla-daemon
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2020-05-06 17:46 ` bugzilla-daemon
2020-05-06 22:06 ` bugzilla-daemon
2020-06-03  0:04 ` [Bug 207383] [Regression] 5.7 " bugzilla-daemon
2020-06-21  7:01 ` bugzilla-daemon
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