On Fri, Aug 21, 2015 at 1:31 PM, Sasha Levin <sasha.le...@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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/