linux-kernel - Re: perf_fuzzer crash on pentium 4

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Message-ID: <20140508020050.GX39568@redhat.com>
Date:	Wed, 7 May 2014 22:00:50 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: perf_fuzzer crash on pentium 4

On Wed, May 07, 2014 at 12:23:08AM +0400, Cyrill Gorcunov wrote:
> On Tue, May 06, 2014 at 11:42:58AM -0400, Vince Weaver wrote:
> > 
> > So just to be difficult I fired up the perf_fuzzer on a Pentium 4 machine.
> > 
> > It crashes more or less instantly (sorry for the line wrapping, 
> > just got the serial console hooked up and don't have minicom configured 
> > right yet).
> > 
> > this is 3.15-rc4 with the anti-memory corruption patch applied.
> > 
> > [   67.872274] BUG: unable to handle kernel NULL pointer dereference at 00000004
> > [   67.876146] IP: [<ffffffff81013df2>] p4_pmu_schedule_events+0xa5/0x331
> 
> This looks like
> 
> p4_pmu_schedule_events:
> 		...
> 		bind = p4_config_get_bind(hwc->config);
> 			returned bind = NULL;
> 		escr_idx = p4_get_escr_idx(bind->escr_msr[thread]); NULL deref
> 
> If i'm right (btw it's possible to use addr2line helper?) then hwc->config
> is corrupted and p4_config_get_bind returned nil simply because proper event
> was not found. And I don't understand how it could happen because before
> configuration gets written into hwc->config it's validated once obtained
> from user-space as a raw event. Weird...

I think my commit 13beacee817d27a40ffc6f065ea0042685611dd5 explains this
corruption.  Though I have to admit I haven't looked through the problem
very closely yet.

IOW my lazy fix in that commit doesn't cover fuzzers and the real problem
in p4_pmu_schedule_events. :-)

Cheers,
Don
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