[PATCH 1/8] perf/x86/intel: Fix memory corruption

[Peter Zijlstra]

Through:

  validate_event()
    x86_pmu.get_event_constraints(.idx=-1)
      tfa_get_event_constraints()
        dyn_constraint()

We use cpuc->constraint_list[-1], which is an obvious out-of-bound
access.

In this case, simply skip the TFA constraint code, there is no event
constraint with just PMC3, therefore the code will never result in the
empty set.

Reported-by: Tony Jones <tonyj@xxxxxxxx>
Reported-by: "DSouza, Nelson" <nelson.dsouza@xxxxxxxxx>
Tested-by: Tony Jones <tonyj@xxxxxxxx>
Tested-by: "DSouza, Nelson" <nelson.dsouza@xxxxxxxxx>
Cc: stable@xxxxxxxxxx
Fixes: 400816f60c54 ("perf/x86/intel: Implement support for TSX Force Abort")
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 arch/x86/events/intel/core.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3410,7 +3410,7 @@ tfa_get_event_constraints(struct cpu_hw_
 	/*
 	 * Without TFA we must not use PMC3.
 	 */
-	if (!allow_tsx_force_abort && test_bit(3, c->idxmsk)) {
+	if (!allow_tsx_force_abort && test_bit(3, c->idxmsk) && idx >= 0) {
 		c = dyn_constraint(cpuc, c, idx);
 		c->idxmsk64 &= ~(1ULL << 3);
 		c->weight--;