Subject: grsecurity: GRKERNSEC_PERF_HARDEN
Origin: https://grsecurity.net/test/grsecurity-3.1-4.1.3-201507261932.patch

The GRKERNSEC_PERF_HARDEN feature extracted from grsecurity.  Adds the
option to disable perf_event_open() entirely for unprivileged users.
This standalone version doesn't include making the variable read-only
(or renaming it).