perf: Limit perf_event_attr:: sample_period to 63 bits

Commit-ID:  0819b2e30ccb93edf04876237b6205eef84ec8d2
Gitweb:     http://git.kernel.org/tip/0819b2e30ccb93edf04876237b6205eef84ec8d2
Author:     Peter Zijlstra <[email protected]>
AuthorDate: Thu, 15 May 2014 20:23:48 +0200
Committer:  Thomas Gleixner <[email protected]>
CommitDate: Mon, 19 May 2014 21:44:55 +0900

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.

---
 kernel/events/core.c | 3 +++
 1 file changed, 3 insertions(+)

index 7123284..1d1ec64 100644
@@ -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;
 	}
 
 	/*