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>
Gbp-Pq: Topic features/all
Gbp-Pq: Name security-perf-allow-further-restriction-of-perf_event_open.patch

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index e657916c9509cfede199a3c3b23f90a9d1e36edc..5f895c79cd6dcb8e2c2046dbcefd85d62779cb07 100644 (file)
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1579,6 +1579,11 @@ int perf_cpu_time_max_percent_handler(struct ctl_table *table, int write,
 int perf_event_max_stack_handler(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
 

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 78ae7b6f90fdbf8c4b509ebba86eacc25f0050e8..5a11101495641fcb44f598c3fd0ad3c75f37d91e 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -414,8 +414,13 @@ static struct kmem_cache *perf_event_cache;
  *   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 */
@@ -12360,6 +12365,9 @@ 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)

diff --git a/security/Kconfig b/security/Kconfig
index 52c9af08ad35d3d31995337d4643b26c015f75ca..2a4686048fffdb0961db01eb21cd4ee3f24d41b7 100644 (file)
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -19,6 +19,15 @@ config SECURITY_DMESG_RESTRICT
 
          If you are unsure how to answer this question, answer N.
 
+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