perf_counter: sysctl for system wide perf counters

Impact: add sysctl for paranoid/relaxed perfcounters policy

Allow the use of system wide perf counters to everybody, but provide
a sysctl to disable it for the paranoid security minded.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <20090409085524.514046352@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

3 files changed, 16 insertions, 1 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index c22363a4f746..981432885301 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -568,6 +568,8 @@ struct perf_callchain_entry {
 
 extern struct perf_callchain_entry *perf_callchain(struct pt_regs *regs);
 
+extern int sysctl_perf_counter_priv;
+
 #else
 static inline void
 perf_counter_task_sched_in(struct task_struct *task, int cpu)           { }
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 76376ecb23b5..7efb7ebaaae0 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -42,6 +42,8 @@ static atomic_t nr_mmap_tracking __read_mostly;
 static atomic_t nr_munmap_tracking __read_mostly;
 static atomic_t nr_comm_tracking __read_mostly;
 
+int sysctl_perf_counter_priv __read_mostly; /* do we need to be privileged */
+
 /*
  * Mutex for (sysadmin-configurable) counter reservations:
  */
@@ -1132,7 +1134,7 @@ static struct perf_counter_context *find_get_context(pid_t pid, int cpu)
          */
         if (cpu != -1) {
                 /* Must be root to operate on a CPU counter: */
-                if (!capable(CAP_SYS_ADMIN))
+                if (sysctl_perf_counter_priv && !capable(CAP_SYS_ADMIN))
                         return ERR_PTR(-EACCES);
 
                 if (cpu < 0 || cpu > num_possible_cpus())
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 4286b62b34a0..8ba457838d95 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -49,6 +49,7 @@
 #include <linux/reboot.h>
 #include <linux/ftrace.h>
 #include <linux/slow-work.h>
+#include <linux/perf_counter.h>
 
 #include <asm/uaccess.h>
 #include <asm/processor.h>
@@ -920,6 +921,16 @@ static struct ctl_table kern_table[] = {
                 .child          = slow_work_sysctls,
         },
 #endif
+#ifdef CONFIG_PERF_COUNTERS
+        {
+                .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "perf_counter_privileged",
+                .data           = &sysctl_perf_counter_priv,
+                .maxlen         = sizeof(sysctl_perf_counter_priv),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec,
+        },
+#endif
 /*
  * NOTE: do not add new entries to this table unless you have read
  * Documentation/sysctl/ctl_unnumbered.txt