Messages in this thread | | | Date | Thu, 10 Sep 2015 01:54:18 -0700 | Subject | Re: [PATCH 01/10] perf,x86: Fix event/group validation | From | Stephane Eranian <> |
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On Fri, Aug 21, 2015 at 1:31 PM, Sasha Levin <sasha.levin@oracle.com> wrote: > > On 05/21/2015 07:17 AM, Peter Zijlstra wrote: > > --- a/arch/x86/kernel/cpu/perf_event_intel.c > > +++ b/arch/x86/kernel/cpu/perf_event_intel.c > > @@ -2106,7 +2106,7 @@ static struct event_constraint * > > intel_get_event_constraints(struct cpu_hw_events *cpuc, int idx, > > struct perf_event *event) > > { > > - struct event_constraint *c1 = event->hw.constraint; > > + struct event_constraint *c1 = cpuc->event_constraint[idx]; > > struct event_constraint *c2; > > Hey Peter, > > I was chasing a memory corruption in this area and I think I found > a possible culprit: > > After this patch, In the code above, we'd access "cpuc->event_constraint[idx]" > and read/change memory. > > The problem is that a valid value for idx is also -1, which isn't checked > here, so we end up accessing and possibly corrupting memory that isn't ours. > > I believe your analysis is correct, the following path will create the problem:
validate_group() validate_event() x86_pmu.get_event_constraints(fake_cpuc, -1, event) intel_get_event_constraints(cpuc, idx, event) struct event_constraints *c1 = cpuc->event_constraints[idx];
here idx = -1, and the kernel is accessing an invalid memory location.
If think the code could be changed to:
struct event_constraint *c1 = NULL; if (idx > -1) c1 = cpuc->event_constraints[idx];
idx is not used in the __intel_get_event_constraints() path if I read the code correctly.
Peter?
> > Thanks, > Sasha
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