linux-kernel - [PATCH v2 3/4] perf tool: make Perf tool aware of SELinux access control

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Date:   Wed, 22 Apr 2020 17:45:34 +0300
From:   Alexey Budankov <alexey.budankov@...ux.intel.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>
Cc:     Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "selinux@...r.kernel.org" <selinux@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>
Subject: [PATCH v2 3/4] perf tool: make Perf tool aware of SELinux access
 control


Implement SELinux sysfs check to see if the system is in enforcing
mode and print warning message with pointers to check audit logs.

Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
---
 tools/perf/util/cloexec.c |  4 ++--
 tools/perf/util/evsel.c   | 40 +++++++++++++++++++++++----------------
 2 files changed, 26 insertions(+), 18 deletions(-)

diff --git a/tools/perf/util/cloexec.c b/tools/perf/util/cloexec.c
index a12872f2856a..9c8ec816261b 100644
--- a/tools/perf/util/cloexec.c
+++ b/tools/perf/util/cloexec.c
@@ -65,7 +65,7 @@ static int perf_flag_probe(void)
 		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)));
 
@@ -83,7 +83,7 @@ static int perf_flag_probe(void)
 	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;
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 9fa92649adb4..82492ca12405 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -2514,32 +2514,40 @@ int perf_evsel__open_strerror(struct evsel *evsel, struct target *target,
 			      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,
-				"No permission to enable %s event.\n\n",
+			printed += scnprintf(msg, size,
+				"No permission to enable %s event.\n",
 				perf_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 capability. 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.",
 				 perf_evsel__name(evsel));
-- 
2.24.1