From: Ben Hutchings <ben@decadent.org.uk>
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).

---
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -898,6 +898,11 @@ extern int perf_cpu_time_max_percent_han
 		loff_t *ppos);
 
 
+static inline bool perf_paranoid_any(void)
+{
+	return sysctl_perf_event_paranoid > 2;
+}
+
 static inline bool perf_paranoid_tracepoint_raw(void)
 {
 	return sysctl_perf_event_paranoid > -1;
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -174,8 +174,13 @@ static struct srcu_struct pmus_srcu;
  *   0 - disallow raw tracepoint access for unpriv
  *   1 - disallow cpu events for unpriv
  *   2 - disallow kernel profiling for unpriv
+ *   3 - disallow all unpriv perf event use
  */
+#ifdef CONFIG_GRKERNSEC_PERF_HARDEN
+int sysctl_perf_event_paranoid __read_mostly = 3;
+#else
 int sysctl_perf_event_paranoid __read_mostly = 1;
+#endif
 
 /* Minimum for 512 kiB + 1 user control page */
 int sysctl_perf_event_mlock __read_mostly = 512 + (PAGE_SIZE / 1024); /* 'free' kiB per user */
@@ -7904,6 +7909,11 @@ SYSCALL_DEFINE5(perf_event_open,
 	if (flags & ~PERF_FLAG_ALL)
 		return -EINVAL;
 
+#ifdef CONFIG_GRKERNSEC_PERF_HARDEN
+	if (perf_paranoid_any() && !capable(CAP_SYS_ADMIN))
+		return -EACCES;
+#endif
+
 	err = perf_copy_attr(attr_uptr, &attr);
 	if (err)
 		return err;
--- a/grsecurity/Kconfig
+++ b/grsecurity/Kconfig
@@ -1,3 +1,21 @@
 #
 # grecurity configuration
 #
+config GRKERNSEC_PERF_HARDEN
+	bool "Disable unprivileged PERF_EVENTS usage by default"
+	depends on PERF_EVENTS
+	help
+	  If you say Y here, the range of acceptable values for the
+	  /proc/sys/kernel/perf_event_paranoid sysctl will be expanded to allow and
+	  default to a new value: 3.  When the sysctl is set to this value, no
+	  unprivileged use of the PERF_EVENTS syscall interface will be permitted.
+
+	  Though PERF_EVENTS can be used legitimately for performance monitoring
+	  and low-level application profiling, it is forced on regardless of
+	  configuration, has been at fault for several vulnerabilities, and
+	  creates new opportunities for side channels and other information leaks.
+
+	  This feature puts PERF_EVENTS into a secure default state and permits
+	  the administrator to change out of it temporarily if unprivileged
+	  application profiling is needed.
+
