perf/x86/intel: Fix constraint access

commit ebfb4988f0378e2ac3b4a0aa1ea20d724293f392 upstream.

Sasha reported that we can get here with .idx==-1, and
cpuc->event_constraints unallocated.

Suggested-by: Stephane Eranian <eranian@google.com>
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: b371b5943178 ("perf/x86: Fix event/group validation")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c
index 2813ea0..2221261 100644 (file)
--- a/arch/x86/kernel/cpu/perf_event_intel.c
+++ b/arch/x86/kernel/cpu/perf_event_intel.c
@@ -2098,9 +2098,12 @@ static struct event_constraint *
 intel_get_event_constraints(struct cpu_hw_events *cpuc, int idx,
                            struct perf_event *event)
 {
-       struct event_constraint *c1 = cpuc->event_constraint[idx];
+       struct event_constraint *c1 = NULL;
        struct event_constraint *c2;
 
+       if (idx >= 0) /* fake does < 0 */
+               c1 = cpuc->event_constraint[idx];
+
        /*
         * first time only
         * - static constraint: no change across incremental scheduling calls