1 files changed, 21 insertions, 0 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 6e75a5c9412d..6c4e523dc1e2 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7316,6 +7316,21 @@ int perf_event_account_interrupt(struct perf_event *event)
         return __perf_event_account_interrupt(event, 1);
 }
 
+static bool sample_is_allowed(struct perf_event *event, struct pt_regs *regs)
+{
+        /*
+         * Due to interrupt latency (AKA "skid"), we may enter the
+         * kernel before taking an overflow, even if the PMU is only
+         * counting user events.
+         * To avoid leaking information to userspace, we must always
+         * reject kernel samples when exclude_kernel is set.
+         */
+        if (event->attr.exclude_kernel && !user_mode(regs))
+                return false;
+
+        return true;
+}
+
 /*
  * Generic event overflow handling, sampling.
  */
@@ -7337,6 +7352,12 @@ static int __perf_event_overflow(struct perf_event *event,
         ret = __perf_event_account_interrupt(event, throttle);
 
         /*
+         * For security, drop the skid kernel samples if necessary.
+         */
+        if (!sample_is_allowed(event, regs))
+                return ret;
+
+        /*
          * XXX event_limit might not quite work as expected on inherited
          * events
          */