Em Thu, Apr 30, 2020 at 10:16:34AM +0300, Alexey Budankov escreveu: > > Publish instructions on how to apply LSM hooks for access control > to perf_event_open() syscall on Fedora distro with Targeted SELinux > policy and then manage access to the syscall. I'm fixing these up: [acme@five perf]$ am /wb/1.patch Applying: perf docs: introduce security.txt file to document related issues .git/rebase-apply/patch:46: space before tab in indent. wake_alarm .git/rebase-apply/patch:47: space before tab in indent. block_suspend .git/rebase-apply/patch:48: space before tab in indent. audit_read .git/rebase-apply/patch:51: trailing whitespace. .git/rebase-apply/patch:54: trailing whitespace. > Signed-off-by: Alexey Budankov <alexey.budankov@xxxxxxxxxxxxxxx> > --- > tools/perf/Documentation/security.txt | 237 ++++++++++++++++++++++++++ > 1 file changed, 237 insertions(+) > create mode 100644 tools/perf/Documentation/security.txt > > diff --git a/tools/perf/Documentation/security.txt b/tools/perf/Documentation/security.txt > new file mode 100644 > index 000000000000..4fe3b8b1958f > --- /dev/null > +++ b/tools/perf/Documentation/security.txt > @@ -0,0 +1,237 @@ > +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 = <setting>) > + > +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 > -- > 2.24.1 > > -- - Arnaldo
