Re: [PATCH] alpha: perf: fix out-of-bounds array access triggered from raw event

[Will Deacon <will.deacon@arm.com>]

Matt,

On Tue, Sep 10, 2013 at 11:19:44AM +0100, Michael Cree wrote:
> On Tue, Sep 10, 2013 at 10:58:12AM +0100, Will Deacon wrote:
> > Vince's perf fuzzer uncovered the following issue on Alpha:
> > 
> > Unable to handle kernel paging request at virtual address fffffbfe4e46a0e8
> > CPU 0 perf_fuzzer(1278): Oops 0
> > pc = [<fffffc000031fbc0>]  ra = [<fffffc000031ff54>]  ps = 0007    Not tainted
> > pc is at alpha_perf_event_set_period+0x60/0xf0
> > ra is at alpha_pmu_enable+0x1a4/0x1c0
> > v0 = 0000000000000000  t0 = 00000000000fffff  t1 = fffffc007b3f5800
> > t2 = fffffbff275faa94  t3 = ffffffffc9b9bd89  t4 = fffffbfe4e46a098
> > t5 = 0000000000000020  t6 = fffffbfe4e46a0b8  t7 = fffffc007f4c8000
> > s0 = 0000000000000000  s1 = fffffc0001b0c018  s2 = fffffc0001b0c020
> > s3 = fffffc007b3f5800  s4 = 0000000000000001  s5 = ffffffffc9b9bd85
> > s6 = 0000000000000001
> > a0 = 0000000000000006  a1 = fffffc007b3f5908  a2 = fffffbfe4e46a098
> > a3 = 00000005000108c0  a4 = 0000000000000000  a5 = 0000000000000000
> > t8 = 0000000000000001  t9 = 0000000000000001  t10= 0000000027829f6f
> > t11= 0000000000000020  pv = fffffc000031fb60  at = fffffc0000950900
> > gp = fffffc0000940900  sp = fffffc007f4cbca8

[...]

> > This patch adds a new callback to alpha_pmu_t for validating the raw
> > event encoding with the Linux event types for the PMU, preventing the
> > out-of-bounds array access.
> > 
> > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > Cc: Michael Cree <mcree@orcon.net.nz>
> > Cc: Matt Turner <mattst88@gmail.com>
> > Signed-off-by: Will Deacon <will.deacon@arm.com>
> 
> Acked-by: Michael Cree <mcree@orcon.net.nz>

I just remembered about this patch whilst cleaning up some old git branches.
Please could you include it in the Alpha tree with a CC stable? Without it,
it's trivial to panic a perf-enabled Alpha kernel from userspace.

Cheers,

Will