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 54e0d31afcad1bb535c6dd513ec45b01cd6e47df..2c6e8badfa274b710c4dea06bb37a84c8e3ac9a2 100644 (file)
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1761,6 +1761,11 @@ extern int sysctl_perf_event_sample_rate;
 
 extern void perf_sample_event_took(u64 sample_len_ns);
 
+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 a9d7ad430135335e51d2b53d889585dbfcd46971..035c34aa730b0d75175a6cb93a710c345b1adfe0 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -463,8 +463,13 @@ 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. 'free' kiB per user. */
 static int sysctl_perf_event_mlock __read_mostly = 512 + (PAGE_SIZE / 1024);
@@ -13392,6 +13397,9 @@ 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(PERF_SECURITY_OPEN);
        if (err)

diff --git a/security/Kconfig b/security/Kconfig
index 285f284dfcac44b60bac80c5e6bd7d4fc39ed8c4..c63f7c6b351cbca1cf9cd3899709522ed0215cd5 100644 (file)
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -72,6 +72,15 @@ config MSEAL_SYSTEM_MAPPINGS
          For complete descriptions of memory sealing, please see
          Documentation/userspace-api/mseal.rst
 
+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