perf tool: Make perf tool aware of SELinux access control

Implement selinux sysfs check to see the system is in enforcing mode and
print warning message with pointer to check audit logs.

Signed-off-by: Alexey Budankov <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Link: http://lore.kernel.org/lkml/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/cloexec.c

···
 		return 1;
 	}
 
-	WARN_ONCE(err != EINVAL && err != EBUSY,
+	WARN_ONCE(err != EINVAL && err != EBUSY && err != EACCES,
 		  "perf_event_open(..., PERF_FLAG_FD_CLOEXEC) failed with unexpected error %d (%s)\n",
 		  err, str_error_r(err, sbuf, sizeof(sbuf)));
 
···
 	if (fd >= 0)
 		close(fd);
 
-	if (WARN_ONCE(fd < 0 && err != EBUSY,
+	if (WARN_ONCE(fd < 0 && err != EBUSY && err != EACCES,
 		      "perf_event_open(..., 0) failed unexpectedly with error %d (%s)\n",
 		      err, str_error_r(err, sbuf, sizeof(sbuf))))
 		return -1;

tools/perf/util/evsel.c

···
 			 int err, char *msg, size_t size)
 {
 	char sbuf[STRERR_BUFSIZE];
-	int printed = 0;
+	int printed = 0, enforced = 0;
 
 	switch (err) {
 	case EPERM:
 	case EACCES:
+		printed += scnprintf(msg + printed, size - printed,
+			"Access to performance monitoring and observability operations is limited.\n");
+
+		if (!sysfs__read_int("fs/selinux/enforce", &enforced)) {
+			if (enforced) {
+				printed += scnprintf(msg + printed, size - printed,
+					"Enforced MAC policy settings (SELinux) can limit access to performance\n"
+					"monitoring and observability operations. Inspect system audit records for\n"
+					"more perf_event access control information and adjusting the policy.\n");
+			}
+		}
+
 		if (err == EPERM)
-			printed = scnprintf(msg, size,
+			printed += scnprintf(msg, size,
 				"No permission to enable %s event.\n\n", evsel__name(evsel));
 
 		return scnprintf(msg + printed, size - printed,
-		 "You may not have permission to collect %sstats.\n\n"
-		 "Consider tweaking /proc/sys/kernel/perf_event_paranoid,\n"
-		 "which controls use of the performance events system by\n"
-		 "unprivileged users (without CAP_PERFMON or CAP_SYS_ADMIN).\n\n"
-		 "The current value is %d:\n\n"
+		 "Consider adjusting /proc/sys/kernel/perf_event_paranoid setting to open\n"
+		 "access to performance monitoring and observability operations for users\n"
+		 "without CAP_PERFMON or CAP_SYS_ADMIN Linux capability.\n"
+		 "perf_event_paranoid setting is %d:\n"
 		 "  -1: Allow use of (almost) all events by all users\n"
 		 "      Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK\n"
-		 ">= 0: Disallow ftrace function tracepoint by users without CAP_PERFMON or CAP_SYS_ADMIN\n"
-		 "      Disallow raw tracepoint access by users without CAP_SYS_PERFMON or CAP_SYS_ADMIN\n"
-		 ">= 1: Disallow CPU event access by users without CAP_PERFMON or CAP_SYS_ADMIN\n"
-		 ">= 2: Disallow kernel profiling by users without CAP_PERFMON or CAP_SYS_ADMIN\n\n"
-		 "To make this setting permanent, edit /etc/sysctl.conf too, e.g.:\n\n"
-		 "	kernel.perf_event_paranoid = -1\n" ,
-				 target->system_wide ? "system-wide " : "",
-				 perf_event_paranoid());
+		 ">= 0: Disallow raw and ftrace function tracepoint access\n"
+		 ">= 1: Disallow CPU event access\n"
+		 ">= 2: Disallow kernel profiling\n"
+		 "To make the adjusted perf_event_paranoid setting permanent preserve it\n"
+		 "in /etc/sysctl.conf (e.g. kernel.perf_event_paranoid = <setting>)",
+		 perf_event_paranoid());
 	case ENOENT:
 		return scnprintf(msg, size, "The %s event is not supported.", evsel__name(evsel));
 	case EMFILE: