From: Ben Hutchings <ben@decadent.org.uk>
Date: Mon, 11 Jan 2016 15:23:55 +0000
Subject: security,perf: Allow further restriction of perf_event_open
Forwarded: https://lore.kernel.org/all/20160111152355.GS28542@decadent.org.uk/

When kernel.perf_event_open is set to 3 (or greater), disallow all
access to performance events by users without CAP_SYS_ADMIN.
Add a Kconfig symbol CONFIG_SECURITY_PERF_EVENTS_RESTRICT that
makes this value the default.

This is based on a similar feature in grsecurity
(CONFIG_GRKERNSEC_PERF_HARDEN).  This version doesn't include making
the variable read-only.  It also allows enabling further restriction
at run-time regardless of whether the default is changed.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 include/linux/perf_event.h | 5 +++++
 kernel/events/core.c       | 8 ++++++++
 security/Kconfig           | 9 +++++++++
 3 files changed, 22 insertions(+)

--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1589,6 +1589,11 @@ int perf_cpu_time_max_percent_handler(co
 int perf_event_max_stack_handler(const struct ctl_table *table, int write,
 		void *buffer, size_t *lenp, loff_t *ppos);
 
+static inline bool perf_paranoid_any(void)
+{
+	return sysctl_perf_event_paranoid > 2;
+}
+
 /* Access to perf_event_open(2) syscall. */
 #define PERF_SECURITY_OPEN		0
 
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -419,8 +419,13 @@ static struct kmem_cache *perf_event_cac
  *   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_SECURITY_PERF_EVENTS_RESTRICT
+int sysctl_perf_event_paranoid __read_mostly = 3;
+#else
 int sysctl_perf_event_paranoid __read_mostly = 2;
+#endif
 
 /* Minimum for 512 kiB + 1 user control page */
 int sysctl_perf_event_mlock __read_mostly = 512 + (PAGE_SIZE / 1024); /* 'free' kiB per user */
@@ -12506,6 +12511,9 @@ SYSCALL_DEFINE5(perf_event_open,
 	if (err)
 		return err;
 
+	if (perf_paranoid_any() && !capable(CAP_SYS_ADMIN))
+		return -EACCES;
+
 	/* Do we allow access to perf_event_open(2) ? */
 	err = security_perf_event_open(&attr, PERF_SECURITY_OPEN);
 	if (err)
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -51,6 +51,15 @@ config PROC_MEM_NO_FORCE
 
 endchoice
 
+config SECURITY_PERF_EVENTS_RESTRICT
+	bool "Restrict unprivileged use of performance events"
+	depends on PERF_EVENTS
+	help
+	  If you say Y here, the kernel.perf_event_paranoid sysctl
+	  will be set to 3 by default, and no unprivileged use of the
+	  perf_event_open syscall will be permitted unless it is
+	  changed.
+
 config SECURITY
 	bool "Enable different security models"
 	depends on SYSFS
