Re: [PATCH v1] perf tool: make Perf tool aware of SELinux access control

[Alexey Budankov]

Hi,

Is there any thougts, comments or questions so far?
Please share you mind.

Thanks,
Alexey

On 13.03.2020 20:27, Alexey Budankov wrote:
> 
> 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@xxxxxxxxxxxxxxx>
> ---
>  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));
>