linux-kernel - Re: perf_fuzzer crash on pentium 4

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Date:	Wed, 7 May 2014 12:46:24 -0400 (EDT)
From:	Vince Weaver <vincent.weaver@...ne.edu>
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, 7 May 2014, Cyrill Gorcunov wrote:

> On Tue, May 06, 2014 at 05:30:19PM -0400, Vince Weaver wrote:
> > On Wed, 7 May 2014, Cyrill Gorcunov wrote:
> > 
> > > > [   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?) 
> > 
> > Yes, the address maps to
> > 
> > 	escr_idx = p4_get_escr_idx(bind->escr_msr[thread]);
> 
> Great, now we knows the reason of the issue, only to figure out
> why is left ;)
> 
> > > 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'll try to get some sort of trace out if it to see what event is being 
> > tried.
> 
> Yeah, this would help a lot.

sorry for the delay, I like to compile kernels locally and it takes a 
really long time to build a ftrace-enabled kernel on a pentium 4 it seems.

Anyway I threw some printks in, and this is what I get:

[  447.572626] VMW: bind=NULL config=6b6b6b6b6b6b6b6b

I have slab poisoning turned on.  Use after free?

Vince
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