[PATCH v1 3/3] perf tool: extend Perf tool with CAP_SYS_PERFMON support

[Alexey Budankov]

Extend error messages to mention CAP_SYS_PERFMON capability as an option
to substitute CAP_SYS_ADMIN credentials where applicable. 

Make perf_event_paranoid_check() to be aware of CAP_SYS_PERFMON in case
perf_event_paranoid value >= 0.

Signed-off-by: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx>
---
 tools/perf/design.txt   |  3 ++-
 tools/perf/util/cap.h   |  4 ++++
 tools/perf/util/evsel.c | 10 +++++-----
 tools/perf/util/util.c  | 15 +++++++++++++--
 4 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/tools/perf/design.txt b/tools/perf/design.txt
index 0453ba26cdbd..71755b3e1303 100644
--- a/tools/perf/design.txt
+++ b/tools/perf/design.txt
@@ -258,7 +258,8 @@ gets schedule to. Per task counters can be created by any user, for
 their own tasks.
 
 A 'pid == -1' and 'cpu == x' counter is a per CPU counter that counts
-all events on CPU-x. Per CPU counters need CAP_SYS_ADMIN privilege.
+all events on CPU-x. Per CPU counters need CAP_SYS_PERFMON or
+CAP_SYS_ADMIN privilege.
 
 The 'flags' parameter is currently unused and must be zero.
 
diff --git a/tools/perf/util/cap.h b/tools/perf/util/cap.h
index 051dc590ceee..0f79fbf6638b 100644
--- a/tools/perf/util/cap.h
+++ b/tools/perf/util/cap.h
@@ -29,4 +29,8 @@ static inline bool perf_cap__capable(int cap __maybe_unused)
 #define CAP_SYSLOG	34
 #endif
 
+#ifndef CAP_SYS_PERFMON
+#define CAP_SYS_PERFMON 38
+#endif
+
 #endif /* __PERF_CAP_H */
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index f4dea055b080..3a46325e3702 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -2468,14 +2468,14 @@ int perf_evsel__open_strerror(struct evsel *evsel, struct target *target,
 		 "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_SYS_ADMIN).\n\n"
+		 "unprivileged users (without CAP_SYS_PERFMON or CAP_SYS_ADMIN).\n\n"
 		 "The current value is %d:\n\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_SYS_ADMIN\n"
-		 "      Disallow raw tracepoint access by users without CAP_SYS_ADMIN\n"
-		 ">= 1: Disallow CPU event access by users without CAP_SYS_ADMIN\n"
-		 ">= 2: Disallow kernel profiling by users without CAP_SYS_ADMIN\n\n"
+		 ">= 0: Disallow ftrace function tracepoint by users without CAP_SYS_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_SYS_PERFMON or CAP_SYS_ADMIN\n"
+		 ">= 2: Disallow kernel profiling by users without CAP_SYS_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 " : "",
diff --git a/tools/perf/util/util.c b/tools/perf/util/util.c
index 969ae560dad9..d8334fa97c85 100644
--- a/tools/perf/util/util.c
+++ b/tools/perf/util/util.c
@@ -271,8 +271,19 @@ int perf_event_paranoid(void)
 
 bool perf_event_paranoid_check(int max_level)
 {
-	return perf_cap__capable(CAP_SYS_ADMIN) ||
-			perf_event_paranoid() <= max_level;
+	bool res = false;
+
+	res = perf_cap__capable(CAP_SYS_ADMIN);
+
+	if (!res) {
+		if (max_level >= 0)
+			res = perf_cap__capable(CAP_SYS_PERFMON);
+	}
+
+	if (!res)
+		res = perf_event_paranoid() <= max_level;
+
+	return res;
 }
 
 static int
-- 
2.20.1