Overview ======== For general security related questions of perf_event_open() syscall usage, performance monitoring and observability operations by Perf see here: https://www.kernel.org/doc/html/latest/admin-guide/perf-security.html Enabling LSM based mandatory access control (MAC) to perf_event_open() syscall ============================================================================== LSM hooks for mandatory access control for perf_event_open() syscall can be used starting from Linux v5.3. Below are the steps to extend Fedora (v31) with Targeted policy with perf_event_open() access control capabilities: 1. Download selinux-policy SRPM package (e.g. selinux-policy-3.14.4-48.fc31.src.rpm on FC31) and install it so rpmbuild directory would exist in the current working directory: # rpm -Uhv selinux-policy-3.14.4-48.fc31.src.rpm 2. Get into rpmbuild/SPECS directory and unpack the source code: # rpmbuild -bp selinux-policy.spec 3. Place patch below at rpmbuild/BUILD/selinux-policy-b86eaaf4dbcf2d51dd4432df7185c0eaf3cbcc02 directory and apply it: # patch -p1 < selinux-policy-perf-events-perfmon.patch patching file policy/flask/access_vectors patching file policy/flask/security_classes # cat selinux-policy-perf-events-perfmon.patch diff -Nura a/policy/flask/access_vectors b/policy/flask/access_vectors --- a/policy/flask/access_vectors 2020-02-04 18:19:53.000000000 +0300 +++ b/policy/flask/access_vectors 2020-02-28 23:37:25.000000000 +0300 @@ -174,6 +174,7 @@ wake_alarm block_suspend audit_read + perfmon } # @@ -1099,3 +1100,15 @@ class xdp_socket inherits socket + +class perf_event +{ + open + cpu + kernel + tracepoint + read + write +} + + diff -Nura a/policy/flask/security_classes b/policy/flask/security_classes --- a/policy/flask/security_classes 2020-02-04 18:19:53.000000000 +0300 +++ b/policy/flask/security_classes 2020-02-28 21:35:17.000000000 +0300 @@ -200,4 +200,6 @@ class xdp_socket +class perf_event + # FLASK 4. Get into rpmbuild/SPECS directory and build policy packages from patched sources: # rpmbuild --noclean --noprep -ba selinux-policy.spec so you have this: # ls -alh rpmbuild/RPMS/noarch/ total 33M drwxr-xr-x. 2 root root 4.0K Mar 20 12:16 . drwxr-xr-x. 3 root root 4.0K Mar 20 12:16 .. -rw-r--r--. 1 root root 112K Mar 20 12:16 selinux-policy-3.14.4-48.fc31.noarch.rpm -rw-r--r--. 1 root root 1.2M Mar 20 12:17 selinux-policy-devel-3.14.4-48.fc31.noarch.rpm -rw-r--r--. 1 root root 2.3M Mar 20 12:17 selinux-policy-doc-3.14.4-48.fc31.noarch.rpm -rw-r--r--. 1 root root 12M Mar 20 12:17 selinux-policy-minimum-3.14.4-48.fc31.noarch.rpm -rw-r--r--. 1 root root 4.5M Mar 20 12:16 selinux-policy-mls-3.14.4-48.fc31.noarch.rpm -rw-r--r--. 1 root root 111K Mar 20 12:16 selinux-policy-sandbox-3.14.4-48.fc31.noarch.rpm -rw-r--r--. 1 root root 14M Mar 20 12:17 selinux-policy-targeted-3.14.4-48.fc31.noarch.rpm 5. Install SELinux packages from Fedora repo, if not already done so, and update with the patched rpms above: # rpm -Uhv rpmbuild/RPMS/noarch/selinux-policy-* 6. Enable SELinux Permissive mode for Targeted policy, if not already done so: # cat /etc/selinux/config # This file controls the state of SELinux on the system. # SELINUX= can take one of these three values: # enforcing - SELinux security policy is enforced. # permissive - SELinux prints warnings instead of enforcing. # disabled - No SELinux policy is loaded. SELINUX=permissive # SELINUXTYPE= can take one of these three values: # targeted - Targeted processes are protected, # minimum - Modification of targeted policy. Only selected processes are protected. # mls - Multi Level Security protection. SELINUXTYPE=targeted 7. Enable filesystem SELinux labeling at the next reboot: # touch /.autorelabel 8. Reboot machine and it will label filesystems and load Targeted policy into the kernel; 9. Login and check that dmesg output doesn't mention that perf_event class is unknown to SELinux subsystem; 10. Check that SELinux is enabled and in Permissive mode # getenforce Permissive 11. Turn SELinux into Enforcing mode: # setenforce 1 # getenforce Enforcing Opening access to perf_event_open() syscall on Fedora with SELinux ================================================================== Access to performance monitoring and observability operations by Perf can be limited for superuser or CAP_PERFMON or CAP_SYS_ADMIN privileged processes. MAC policy settings (e.g. SELinux) can be loaded into the kernel and prevent unauthorized access to perf_event_open() syscall. In such case Perf tool provides a message similar to the one below: # perf stat Error: Access to performance monitoring and observability operations is limited. Enforced MAC policy settings (SELinux) 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_PERFMON or CAP_SYS_ADMIN Linux 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 = ) To make sure that access is limited by MAC policy settings inspect system audit records using journalctl command or /var/log/audit/audit.log so the output would contain AVC denied records related to perf_event: # journalctl --reverse --no-pager | grep perf_event python3[1318099]: SELinux is preventing perf from open access on the perf_event labeled unconfined_t. If you believe that perf should be allowed open access on perf_event labeled unconfined_t by default. setroubleshoot[1318099]: SELinux is preventing perf from open access on the perf_event labeled unconfined_t. For complete SELinux messages run: sealert -l 4595ce5b-e58f-462c-9d86-3bc2074935de audit[1318098]: AVC avc: denied { open } for pid=1318098 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 In order to open access to perf_event_open() syscall MAC policy settings can require to be extended. On SELinux system this can be done by loading a special policy module extending base policy settings. Perf related policy module can be generated using the system audit records about blocking perf_event access. Run the command below to generate my-perf.te policy extension file with perf_event related rules: # 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 }; Now compile, pack and load my-perf.pp extension module into the kernel: # checkmodule -M -m -o my-perf.mod my-perf.te # semodule_package -o my-perf.pp -m my-perf.mod # semodule -X 300 -i my-perf.pp After all those taken steps above access to perf_event_open() syscall should now be allowed by the policy settings. Check access running Perf like this: # perf stat ^C Performance counter stats for 'system wide': 36,387.41 msec cpu-clock # 7.999 CPUs utilized 2,629 context-switches # 0.072 K/sec 57 cpu-migrations # 0.002 K/sec 1 page-faults # 0.000 K/sec 263,721,559 cycles # 0.007 GHz 175,746,713 instructions # 0.67 insn per cycle 19,628,798 branches # 0.539 M/sec 1,259,201 branch-misses # 6.42% of all branches 4.549061439 seconds time elapsed The generated perf-event.pp related policy extension module can be removed from the kernel using this command: # semodule -X 300 -r my-perf Alternatively the module can be temporarily disabled and enabled back using these two commands: # semodule -d my-perf # semodule -e my-perf If something went wrong ======================= To turn SELinux into Permissive mode: # setenforce 0 To fully disable SELinux during kernel boot [3] set kernel command line parameter selinux=0 To remove SELinux labeling from local filesystems: # find / -mount -print0 | xargs -0 setfattr -h -x security.selinux To fully turn SELinux off a machine set SELINUX=disabled at /etc/selinux/config file and reboot; Links ===== [1] https://download-ib01.fedoraproject.org/pub/fedora/linux/updates/31/Everything/SRPMS/Packages/s/selinux-policy-3.14.4-49.fc31.src.rpm [2] https://docs.fedoraproject.org/en-US/Fedora/11/html/Security-Enhanced_Linux/sect-Security-Enhanced_Linux-Working_with_SELinux-Enabling_and_Disabling_SELinux.html [3] https://danwalsh.livejournal.com/10972.html