security,perf: Allow further restriction of perf_event_open

Forwarded: https://lkml.org/lkml/2016/1/11/587

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 0031f7b4d9aba0407f98da14c6b0ee70176a4a9c..20220b3542ed2e6693eafbd26541122876cca2c1 100644 (file)
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1387,6 +1387,11 @@ 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 7699b99706ad418adaa9b9cd8ddbb22fb28fde31..7e793bf5b7aa8d8682937e952ae901f900cc671c 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -415,8 +415,13 @@ 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 */
@@ -12235,6 +12240,9 @@ 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 e6db09a779b779c4dfebe6910b2338bf7df6c28d..037dc2baba2be541c8dd463e142005428df5b750 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