Changes in v3:
- mention "CAP_PERFMON or CAP_SYS_ADMIN" instead of sole CAP_PERFMON or
CAP_SYS_ADMIN capability in the docs and messages to support use case
of newer Perf tool on kernel w/o CAP_PERFMON
- reverted double new line in "No permission to enable %s event.\n\n"
- updated security.txt content with new messages wording
v2: https://lore.kernel.org/lkml/[email protected]/
Changes in v2:
- implemented minor doc and code changes to substitute CAP_SYS_ADMIN
with CAP_PERFMON capability;
- introduced Perf doc file with instructions on how to enable and use
perf_event LSM hooks for mandatory access control to perf_event_open()
syscall;
v1: https://lore.kernel.org/lkml/[email protected]/
repo: git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git perf/core
sha1: ee097e8ee56f8867cbbf45fe2a06f6b9e660c39c
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. See new added security.txt file for exact steps
how the changes look like and how to test the patch set.
---
Alexey Budankov (3):
perf docs: extend CAP_SYS_ADMIN with CAP_PERFMON where needed
perf tool: make Perf tool aware of SELinux access control
perf docs: introduce security.txt file to document related issues
tools/perf/Documentation/perf-intel-pt.txt | 2 +-
tools/perf/Documentation/security.txt | 237 +++++++++++++++++++++
tools/perf/util/cloexec.c | 4 +-
tools/perf/util/evsel.c | 39 ++--
4 files changed, 264 insertions(+), 18 deletions(-)
create mode 100644 tools/perf/Documentation/security.txt
--
2.24.1
Extend CAP_SYS_ADMIN with CAP_PERFMON in the docs.
Signed-off-by: Alexey Budankov <[email protected]>
---
tools/perf/Documentation/perf-intel-pt.txt | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/perf/Documentation/perf-intel-pt.txt b/tools/perf/Documentation/perf-intel-pt.txt
index 456fdcbf26ac..832408a54c1c 100644
--- a/tools/perf/Documentation/perf-intel-pt.txt
+++ b/tools/perf/Documentation/perf-intel-pt.txt
@@ -687,7 +687,7 @@ The v4.2 kernel introduced support for a context switch metadata event,
PERF_RECORD_SWITCH, which allows unprivileged users to see when their processes
are scheduled out and in, just not by whom, which is left for the
PERF_RECORD_SWITCH_CPU_WIDE, that is only accessible in system wide context,
-which in turn requires CAP_SYS_ADMIN.
+which in turn requires CAP_PERFMON or CAP_SYS_ADMIN.
Please see the 45ac1403f564 ("perf: Add PERF_RECORD_SWITCH to indicate context
switches") commit, that introduces these metadata events for further info.
--
2.24.1
Implement selinux sysfs check to see the system is in enforcing
mode and print warning message with pointer to check audit logs.
Signed-off-by: Alexey Budankov <[email protected]>
---
tools/perf/util/cloexec.c | 4 ++--
tools/perf/util/evsel.c | 39 ++++++++++++++++++++++++---------------
2 files changed, 26 insertions(+), 17 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 9fa92649adb4..bf437c059c2b 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -2514,32 +2514,41 @@ 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,
+ "Enforced MAC policy settings (SELinux) can limit access to performance\n"
+ "monitoring and observability operations. Inspect system audit records for\n"
+ "more perf_event access control information and adjusting the policy.\n");
+ }
+ }
+
if (err == EPERM)
- printed = scnprintf(msg, size,
+ printed += scnprintf(msg, size,
"No permission to enable %s event.\n\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_PERFMON or 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_PERFMON or CAP_SYS_ADMIN Linux capability.\n"
+ "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_PERFMON or CAP_SYS_ADMIN\n"
- " Disallow raw tracepoint access by users without CAP_SYS_PERFMON or CAP_SYS_ADMIN\n"
- ">= 1: Disallow CPU event access by users without CAP_PERFMON or CAP_SYS_ADMIN\n"
- ">= 2: Disallow kernel profiling by users without CAP_PERFMON or 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));
--
2.24.1
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.
Signed-off-by: Alexey Budankov <[email protected]>
---
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