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));
>
