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Date: Wed, 7 May 2014 00:23:08 +0400
From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Vince Weaver <vincent.weaver@maine.edu>
Cc: linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>
Subject: Re: perf_fuzzer crash on pentium 4
Message-ID: <20140506202307.GA1458@moon>
References: <alpine.DEB.2.10.1405061137560.3220@vincent-weaver-1.umelst.maine.edu>
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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...