[PATCH 4/7] perf,x86/msr: Fix possible Spectre-v1 for msr

[Peter Zijlstra]

> arch/x86/events/msr.c:178 msr_event_init() warn: potential spectre issue 'msr' (local cap)

Userspace controls @attr, sanitize cfg (attr->config) before using it
to index an array.

Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
 arch/x86/events/msr.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/arch/x86/events/msr.c
+++ b/arch/x86/events/msr.c
@@ -158,9 +158,6 @@ static int msr_event_init(struct perf_ev
 	if (event->attr.type != event->pmu->type)
 		return -ENOENT;
 
-	if (cfg >= PERF_MSR_EVENT_MAX)
-		return -EINVAL;
-
 	/* unsupported modes and filters */
 	if (event->attr.exclude_user   ||
 	    event->attr.exclude_kernel ||
@@ -171,6 +168,11 @@ static int msr_event_init(struct perf_ev
 	    event->attr.sample_period) /* no sampling */
 		return -EINVAL;
 
+	if (cfg >= PERF_MSR_EVENT_MAX)
+		return -EINVAL;
+
+	cfg = array_index_nospec(cfg, PERF_MSR_EVENT_MAX);
+
 	if (!msr[cfg].attr)
 		return -EINVAL;