[PATCH v1 2/2] perf Documentation: Introduce the sysctl perf_allow_sample_leakage

Jin Yao
2018-06-15T02:10:09Z

Introduce a new sysctl /sys/devices/cpu/perf_allow_sample_leakage, which
turns on/off dropping leaked kernel samples.

Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
---
tools/perf/Documentation/perf-record.txt | 14 ++++++++++++++
1 file changed, 14 insertions(+)

diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 04168da..97fb0f8 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -93,6 +93,20 @@ OPTIONS
prevent the shell interpretation. You also need to use --group on
"perf report" to view group events together.

+ Note that if workload does a lot of kernel entry/exit we may see
+ kernel samples even if :u is specified. That is due to skid existing.
+ This might be a security issue because it can leak kernel address even
+ though kernel sampling support is disabled. We have a sysctl to turn
+ on/off the dropping of leaked kernel samples.
+
+ /sys/devices/cpu/perf_allow_sample_leakage
+
+ 0 - drop the leaked kernel samples, default option.
+ 1 - don't drop the leaked kernel samples.
+
+ For example, write 1 to perf_allow_sample_leakage
+ echo 1 > /sys/devices/cpu/perf_allow_sample_leakage
+
--filter=<filter>::
Event filter. This option should follow a event selector (-e) which
selects either tracepoint event(s) or a hardware trace PMU
--
2.7.4