Re: perf_fuzzer crash on pentium 4

Don Zickus
2014-05-08T02:01:25Z

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