[PATCH v1] perf tool: make Perf tool aware of SELinux access control
Arnaldo Carvalho de Melo
arnaldo.melo at gmail.com
Thu Mar 19 19:01:26 UTC 2020
Em Thu, Mar 19, 2020 at 09:23:30AM +0300, Alexey Budankov escreveu:
> Hi,
>
> Is there any thougts, comments or questions so far?
> Please share you mind.
>From a quick look, seems ok, I'll do some testing now,
- Arnaldo
> 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 at 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 at 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 at host ~]# getenforce
> > Enforcing
> >
> > === Access by unprivileged user ===
> >
> > [user at 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 at 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 at 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 at 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 at host ~]$ libcap/progs/getcap /usr/local/bin/perf.cap
> > /usr/local/bin/perf.cap = cap_sys_ptrace,cap_syslog,cap_sys_admin+ep
> >
> > [user at 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 at 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 at 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 at host ~]# semodule -X 300 -i my-perf.pp
> >
> > [user at 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 at 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 at 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 at 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 at 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));
> >
--
- Arnaldo
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