linux-kernel - Re: perf: perf_fuzzer triggers NULL pointer dereference

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Message-ID: <alpine.DEB.2.21.1811081145220.8092@macbook-air>
Date:   Thu, 8 Nov 2018 11:46:41 -0500 (EST)
From:   Vince Weaver <vincent.weaver@...ne.edu>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>
cc:     Vince Weaver <vincent.weaver@...ne.edu>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        torvalds@...ux-foundation.org
Subject: Re: perf: perf_fuzzer triggers NULL pointer dereference

On Thu, 8 Nov 2018, Alexander Shishkin wrote:

> Vince Weaver <vincent.weaver@...ne.edu> writes:
> 
> > On Thu, 8 Nov 2018, Vince Weaver wrote:
> >
> >> [91760.326510] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
> >> [91760.334876] PGD 0 P4D 0 
> >> [91760.337596] Oops: 0000 [#1] SMP PTI
> >> [91760.341332] CPU: 6 PID: 0 Comm: swapper/6 Tainted: G        W         4.20.0-rc1+ #119
> >> [91760.349816] Hardware name: LENOVO 10AM000AUS/SHARKBAY, BIOS FBKT72AUS 01/26/2014
> >> [91760.357723] RIP: 0010:perf_prepare_sample+0x82/0x4a0
> >
> > so what's the best way to do the equivelent of addr2line on something like 
> > this, now that we aren't allowed to know the RIP anymore?
> 
> scripts/decode_stacktrace.sh works most of the time.
> 
> Sounds like BTS needs fixing up again. Thanks for looking at it though!

In case it matters, it looks like the address of the oops comes down to

	linux.git/kernel/events/core.c:6393

	size += data->callchain->nr;

Vince