perf: Limit perf_event_attr::sample_period to 63 bits

Vince reported that using a large sample_period (one with bit 63 set)
results in wreckage since while the sample_period is fundamentally
unsigned (negative periods don't make sense) the way we implement
things very much rely on signed logic.

So limit sample_period to 63 bits to avoid tripping over this.

Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/n/tip-p25fhunibl4y3qi0zuqmyf4b@git.kernel.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7123284..1d1ec64 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7029,6 +7029,9 @@ SYSCALL_DEFINE5(perf_event_open,
        if (attr.freq) {
                if (attr.sample_freq > sysctl_perf_event_sample_rate)
                        return -EINVAL;
+       } else {
+               if (attr.sample_period & (1ULL << 63))
+                       return -EINVAL;
        }
 
        /*