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From: Alexey Budankov <alexey.budankov@linux.intel.com>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, Andi Kleen <ak@linux.intel.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	"selinux@vger.kernel.org" <selinux@vger.kernel.org>,
	"linux-security-module@vger.kernel.org" 
	<linux-security-module@vger.kernel.org>
Subject: [PATCH v1] perf tool: make Perf tool aware of SELinux access control
Date: Fri, 13 Mar 2020 20:27:40 +0300
Message-ID: <b8a0669e-36e4-a0e8-fd35-3dbd890d2170@linux.intel.com> (raw)


Extend Perf tool with the check of /sys/fs/selinux/enforce value and notify 
in case access to perf_event_open() syscall is restricted by the enforced 
SELinux policy settings.

Testing and evaluation (Fedora 31 x86_64 with enforced Targeted policy extended
by perf_event class (see refpolicy [1] master branch)):

[root@host ~]# ps -Z
LABEL                               PID TTY          TIME CMD
unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 3960 pts/1 00:00:00 bash
unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 4167 pts/1 00:00:00 ps

[root@host ~]# ls -alhZ /usr/local/bin/
total 56M
drwxr-xr-x.  2 root root       system_u:object_r:bin_t:s0     4.0K Mar  4 12:27 .
drwxr-xr-x. 12 root root       system_u:object_r:usr_t:s0     4.0K Jul 25  2019 ..
-rwxr-xr-x.  1 root root       system_u:object_r:bin_t:s0     4.1M Jan 23  2017 bash
-rwxr-xr-x.  1 root root       system_u:object_r:bin_t:s0     4.1M Jan 23  2017 bash.before_shellshock_patch
...
-rwxr-xr-x.  1 root root       system_u:object_r:bin_t:s0      372 May 14  2019 flask
-rwxr-xr-x.  1 root root       unconfined_u:object_r:bin_t:s0  24M Mar  4 12:15 perf     <== unprivileged users (perf_event_paranoid)
-rwxr-x---.  1 root perf_users unconfined_u:object_r:bin_t:s0  24M Mar  4 12:19 perf.cap <== perf_users (CAP_SYS_ADMIN)
-rwxr-xr-x.  1 root root       system_u:object_r:bin_t:s0      44K Dec  8  2016 spiff
...
lrwxrwxrwx.  1 root root       system_u:object_r:bin_t:s0        4 Aug 21  2018 zstdmt -> zstd

[root@host ~]# getenforce
Enforcing

=== Access by unprivileged user ===

[user@host ~]$ ps -Z
LABEL                               PID TTY          TIME CMD
unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 4043 pts/2 00:00:00 bash
unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 4168 pts/2 00:00:00 ps

[user@host ~]$ /usr/local/bin/perf stat -- ls
Error:
Access to performance monitoring and observability operations is limited.
SELinux Enforcing mode is enabled and can limit access to performance
monitoring and observability operations. Inspect system audit records
for more perf_event access control information and adjusting the policy.
Consider adjusting /proc/sys/kernel/perf_event_paranoid setting to open
access to performance monitoring and observability operations for users
without CAP_SYS_ADMIN capability. perf_event_paranoid setting is -1:
  -1: Allow use of (almost) all events by all users
      Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK
>= 0: Disallow raw and ftrace function tracepoint access
>= 1: Disallow CPU event access
>= 2: Disallow kernel profiling
To make the adjusted perf_event_paranoid setting permanent preserve it
in /etc/sysctl.conf (e.g. kernel.perf_event_paranoid = <setting>)

[root@host ~]# journalctl --follow
... audit[4186]: AVC avc:  denied  { open } for  pid=4186 comm="perf" scontext=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 tcontext=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 tclass=perf_event permissive=0
... audit[4186]: AVC avc:  denied  { open } for  pid=4186 comm="perf" scontext=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 tcontext=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 tclass=perf_event permissive=0
... setroubleshoot[4194]: SELinux is preventing perf from open access on the perf_event labeled unconfined_t. For complete SELinux messages run: sealert -l 9a6f3db2-3d8f-461e-afad-0b5c3a9c3b9d
... python3[4194]: SELinux is preventing perf from open access on the perf_event labeled unconfined_t.
                                          
                                          *****  Plugin catchall (100. confidence) suggests   **************************
                                          
                                          If you believe that perf should be allowed open access on perf_event labeled unconfined_t by default.
                                          Then you should report this as a bug.
                                          You can generate a local policy module to allow this access.
                                          Do
                                          allow this access for now by executing:
                                          # ausearch -c 'perf' --raw | audit2allow -M my-perf
                                          # semodule -X 300 -i my-perf.pp
                                          
=== Access by perf privileged user ===

[user@host ~]$ ps -Z
LABEL                               PID TTY          TIME CMD
unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 4043 pts/2 00:00:00 bash
unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 4168 pts/2 00:00:00 ps

[user@host ~]$ libcap/progs/getcap /usr/local/bin/perf.cap
/usr/local/bin/perf.cap = cap_sys_ptrace,cap_syslog,cap_sys_admin+ep

[user@host ~]$ /usr/local/bin/perf.cap stat -- ls
Error:
Access to performance monitoring and observability operations is limited.
SELinux Enforcing mode is enabled and can limit access to performance
monitoring and observability operations. Inspect system audit records
for more perf_event access control information and adjusting the policy.
Consider adjusting /proc/sys/kernel/perf_event_paranoid setting to open
access to performance monitoring and observability operations for users
without CAP_SYS_ADMIN capability. perf_event_paranoid setting is -1:
  -1: Allow use of (almost) all events by all users
      Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK
>= 0: Disallow raw and ftrace function tracepoint access
>= 1: Disallow CPU event access
>= 2: Disallow kernel profiling
To make the adjusted perf_event_paranoid setting permanent preserve it
in /etc/sysctl.conf (e.g. kernel.perf_event_paranoid = <setting>)

[root@host ~]# journalctl --follow

... audit[3926]: AVC avc:  denied  { open } for  pid=3926 comm="perf.cap" scontext=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 tcontext=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 tclass=perf_event permissive=0
... audit[3926]: AVC avc:  denied  { open } for  pid=3926 comm="perf.cap" scontext=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 tcontext=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 tclass=perf_event permissive=0

... setroubleshoot[3934]: SELinux is preventing perf from open access on the perf_event labeled unconfined_t. For complete SELinux messages run: sealert -l 9a6f3db2-3d8f-461e-afad-0b5c3a9c3b9d
... python3[3934]: SELinux is preventing perf from open access on the perf_event labeled unconfined_t.
                                          
                                          *****  Plugin catchall (100. confidence) suggests   **************************
                                          
                                          If you believe that perf should be allowed open access on perf_event labeled unconfined_t by default.
                                          Then you should report this as a bug.
                                          You can generate a local policy module to allow this access.
                                          Do
                                          allow this access for now by executing:
                                          # ausearch -c 'perf' --raw | audit2allow -M my-perf
                                          # semodule -X 300 -i my-perf.pp
                                          
=== Open access to performance monitoring and observability operations in unconfined_t domain ===

[root@host ~]# ausearch -c 'perf' --raw | audit2allow -M my-perf && cat my-perf.te

module my-perf 1.0;

require {
	type unconfined_t;
	class perf_event { cpu kernel open read tracepoint write };
}

#============= unconfined_t ==============
allow unconfined_t self:perf_event { cpu kernel open read tracepoint write };

[root@host ~]# semodule -X 300 -i my-perf.pp

[user@host ~]$ ps -Z
LABEL                               PID TTY          TIME CMD
unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 4043 pts/2 00:00:00 bash
unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 4168 pts/2 00:00:00 ps

[user@host ~]$ /usr/local/bin/perf stat -- ls
Desktop  Documents  Downloads  intel  Music  perf.data	perf.data.old  Pictures  Public  Templates  Videos

 Performance counter stats for 'ls':

              0.72 msec task-clock:u              #    0.655 CPUs utilized          
                 0      context-switches:u        #    0.000 K/sec                  
                 0      cpu-migrations:u          #    0.000 K/sec                  
                98      page-faults:u             #    0.137 M/sec                  
           908,356      cycles:u                  #    1.266 GHz                    
           729,984      instructions:u            #    0.80  insn per cycle         
           142,774      branches:u                #  198.968 M/sec                  
             8,238      branch-misses:u           #    5.77% of all branches        

       0.001095239 seconds time elapsed

       0.001147000 seconds user
       0.000000000 seconds sys

[user@host ~]$ /usr/local/bin/perf stat -a
Error:
Access to performance monitoring and observability operations is limited.
SELinux Enforcing mode is enabled and can limit access to performance
monitoring and observability operations. Inspect system audit records
for more perf_event access control information and adjusting the policy.
Consider adjusting /proc/sys/kernel/perf_event_paranoid setting to open
access to performance monitoring and observability operations for users
without CAP_SYS_ADMIN capability. perf_event_paranoid setting is -1:
  -1: Allow use of (almost) all events by all users
      Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK
>= 0: Disallow raw and ftrace function tracepoint access
>= 1: Disallow CPU event access
>= 2: Disallow kernel profiling
To make the adjusted perf_event_paranoid setting permanent preserve it
in /etc/sysctl.conf (e.g. kernel.perf_event_paranoid = <setting>)

[user@host ~]$ /usr/local/bin/perf.cap stat -a
^C
 Performance counter stats for 'system wide':

         13,427.05 msec cpu-clock                 #    7.997 CPUs utilized          
               783      context-switches          #    0.058 K/sec                  
                29      cpu-migrations            #    0.002 K/sec                  
                 6      page-faults               #    0.000 K/sec                  
       161,084,874      cycles                    #    0.012 GHz                    
       146,823,131      instructions              #    0.91  insn per cycle         
        12,164,802      branches                  #    0.906 M/sec                  
           380,350      branch-misses             #    3.13% of all branches        

       1.678938906 seconds time elapsed

[1] https://github.com/SELinuxProject/refpolicy

Signed-off-by: Alexey Budankov <alexey.budankov@linux.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 816d930d774e..f03ce1d362d3 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -2493,32 +2493,40 @@ 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,
+					"SELinux Enforcing mode is enabled and can limit access to performance\n"
+					"monitoring and observability operations. Inspect system audit records\n"
+					"for 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_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_SYS_ADMIN 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_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"
-		 "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


             reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-13 17:27 Alexey Budankov [this message]
2020-03-19  6:23 ` Alexey Budankov
2020-03-19 19:01   ` Arnaldo Carvalho de Melo
2020-03-19 19:05     ` Arnaldo Carvalho de Melo
2020-03-20 12:24       ` Alexey Budankov
2020-03-20 13:48         ` Arnaldo Carvalho de Melo

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