[tip:perf/urgent] perf: Limit perf_event_attr:: sample_period to 63 bits

[tip-bot for Peter Zijlstra]

Commit-ID:  0819b2e30ccb93edf04876237b6205eef84ec8d2
Gitweb:     http://git.kernel.org/tip/0819b2e30ccb93edf04876237b6205eef84ec8d2
Author:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Thu, 15 May 2014 20:23:48 +0200
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
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.

Reported-by: Vince Weaver <vincent.weaver@xxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/n/tip-p25fhunibl4y3qi0zuqmyf4b@xxxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
 kernel/events/core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 7123284..1d1ec64 100644
--- 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;
 	}
 
 	/*
--
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