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

From: Arnaldo Carvalho de Melo
Date: Thu Mar 19 2020 - 15:05:19 EST

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Em Thu, Mar 19, 2020 at 04:01:26PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Thu, Mar 19, 2020 at 09:23:30AM +0300, Alexey Budankov escreveu:
> > 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,

> > 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)):

So I'll try the steps below with/without your patch, and then... what
are the steps that a tester needs to go thru to have that refpolicy in?
Install some new SELinux package or library, spelling out in detail the
steps one needs to go thru helps reviewing/testing,

- Arnaldo

> > > [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));
> > >
>
> --
>
> - Arnaldo

--

- Arnaldo

Next message: syzbot: "general protection fault in sctp_ulpevent_nofity_peer_addr_change"
Previous message: Daniel Jordan: "Re: [PATCH v3] mm: fix tick timer stall during deferred page init"
In reply to: Arnaldo Carvalho de Melo: "Re: [PATCH v1] perf tool: make Perf tool aware of SELinux access control"
Next in thread: Alexey Budankov: "Re: [PATCH v1] perf tool: make Perf tool aware of SELinux access control"
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