linux-kernel - Re: [BUG] completely bonkers use of set_need_resched + VM_FAULT

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Message-ID: <CAKMK7uHJansZzKxrr8p0c2X5pEeb-BSxLa6=tnsDmwo-k__Xcg@mail.gmail.com>
Date:	Thu, 12 Sep 2013 22:04:03 +0200
From:	Daniel Vetter <daniel.vetter@...ll.ch>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Dave Airlie <airlied@...ux.ie>,
	Maarten Lankhorst <maarten.lankhorst@...onical.com>,
	Thomas Hellstrom <thellstrom@...are.com>,
	intel-gfx <intel-gfx@...ts.freedesktop.org>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [BUG] completely bonkers use of set_need_resched + VM_FAULT_NOPAGE

On Thu, Sep 12, 2013 at 9:58 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
>
>> On Thu, Sep 12, 2013 at 6:22 PM, Peter Zijlstra <peterz@...radead.org> wrote:
>> > If 'sane' userspace is never supposed to do this, then only insane
>> > userspace is going to hurt from this and that's a GOOD (tm) thing,
>> > right? ;-)
>>
>> Afaik sane userspace doesn't hit the _deadlock_ (or lifelock if we
>> have the set_need_resched in there). drm/i915 is a bit different since
>> we have just one lock, and so the same design would actually deadlock
>> even for sane userspace. But hitting contention there and yielding is
>> somewhat expected. Obviously shouldn't happen too often since it'll
>> hurt performance, with either blocking or the yield spinning loop.
>
> So this is actually a non priviledged DoS interface, right?

I think for ttm drivers it's just execbuf being exploitable. But on
drm/i915 we've
had the same issue with the pwrite/pread ioctls, so a simple
glBufferData(glMap) kind of recursion from gl clients blew the kernel
to pieces ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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