perf_event: Add support for LSM and SELinux checks

In current mainline, the degree of access to perf_event_open(2) system
call depends on the perf_event_paranoid sysctl.  This has a number of
limitations:

1. The sysctl is only a single value. Many types of accesses are controlled
   based on the single value thus making the control very limited and
   coarse grained.
2. The sysctl is global, so if the sysctl is changed, then that means
   all processes get access to perf_event_open(2) opening the door to
   security issues.

This patch adds LSM and SELinux access checking which will be used in
Android to access perf_event_open(2) for the purposes of attaching BPF
programs to tracepoints, perf profiling and other operations from
userspace. These operations are intended for production systems.

5 new LSM hooks are added:
1. perf_event_open: This controls access during the perf_event_open(2)
   syscall itself. The hook is called from all the places that the
   perf_event_paranoid sysctl is checked to keep it consistent with the
   systctl. The hook gets passed a 'type' argument which controls CPU,
   kernel and tracepoint accesses (in this context, CPU, kernel and
   tracepoint have the same semantics as the perf_event_paranoid sysctl).
   Additionally, I added an 'open' type which is similar to
   perf_event_paranoid sysctl == 3 patch carried in Android and several other
   distros but was rejected in mainline [1] in 2016.

2. perf_event_alloc: This allocates a new security object for the event
   which stores the current SID within the event. It will be useful when
   the perf event's FD is passed through IPC to another process which may
   try to read the FD. Appropriate security checks will limit access.

3. perf_event_free: Called when the event is closed.

4. perf_event_read: Called from the read(2) and mmap(2) syscalls for the event.

5. perf_event_write: Called from the ioctl(2) syscalls for the event.

[1] https://lwn.net/Articles/696240/

Since Peter had suggest LSM hooks in 2016 [1], I am adding his
Suggested-by tag below.

To use this patch, we set the perf_event_paranoid sysctl to -1 and then
apply selinux checking as appropriate (default deny everything, and then
add policy rules to give access to domains that need it). In the future
we can remove the perf_event_paranoid sysctl altogether.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Co-developed-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: James Morris <jmorris@namei.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: rostedt@goodmis.org
Cc: Yonghong Song <yhs@fb.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: jeffv@google.com
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: primiano@google.com
Cc: Song Liu <songliubraving@fb.com>
Cc: rsavitski@google.com
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Matthew Garrett <matthewgarrett@google.com>
Link: https://lkml.kernel.org/r/20191014170308.70668-1-joel@joelfernandes.org

1 files changed, 69 insertions, 0 deletions

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 9625b99e677f..28eb05490d59 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -6795,6 +6795,67 @@ struct lsm_blob_sizes selinux_blob_sizes __lsm_ro_after_init = {
 	.lbs_msg_msg = sizeof(struct msg_security_struct),
 };
 
+#ifdef CONFIG_PERF_EVENTS
+static int selinux_perf_event_open(struct perf_event_attr *attr, int type)
+{
+	u32 requested, sid = current_sid();
+
+	if (type == PERF_SECURITY_OPEN)
+		requested = PERF_EVENT__OPEN;
+	else if (type == PERF_SECURITY_CPU)
+		requested = PERF_EVENT__CPU;
+	else if (type == PERF_SECURITY_KERNEL)
+		requested = PERF_EVENT__KERNEL;
+	else if (type == PERF_SECURITY_TRACEPOINT)
+		requested = PERF_EVENT__TRACEPOINT;
+	else
+		return -EINVAL;
+
+	return avc_has_perm(&selinux_state, sid, sid, SECCLASS_PERF_EVENT,
+			    requested, NULL);
+}
+
+static int selinux_perf_event_alloc(struct perf_event *event)
+{
+	struct perf_event_security_struct *perfsec;
+
+	perfsec = kzalloc(sizeof(*perfsec), GFP_KERNEL);
+	if (!perfsec)
+		return -ENOMEM;
+
+	perfsec->sid = current_sid();
+	event->security = perfsec;
+
+	return 0;
+}
+
+static void selinux_perf_event_free(struct perf_event *event)
+{
+	struct perf_event_security_struct *perfsec = event->security;
+
+	event->security = NULL;
+	kfree(perfsec);
+}
+
+static int selinux_perf_event_read(struct perf_event *event)
+{
+	struct perf_event_security_struct *perfsec = event->security;
+	u32 sid = current_sid();
+
+	return avc_has_perm(&selinux_state, sid, perfsec->sid,
+			    SECCLASS_PERF_EVENT, PERF_EVENT__READ, NULL);
+}
+
+static int selinux_perf_event_write(struct perf_event *event)
+{
+	struct perf_event_security_struct *perfsec = event->security;
+	u32 sid = current_sid();
+
+	return avc_has_perm(&selinux_state, sid, perfsec->sid,
+			    SECCLASS_PERF_EVENT, PERF_EVENT__WRITE, NULL);
+}
+#endif
+
 static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(binder_set_context_mgr, selinux_binder_set_context_mgr),
 	LSM_HOOK_INIT(binder_transaction, selinux_binder_transaction),
@@ -7030,6 +7091,14 @@ static struct security_hook_list selinux_hooks[] __lsm_ro_after_init = {
 	LSM_HOOK_INIT(bpf_map_free_security, selinux_bpf_map_free),
 	LSM_HOOK_INIT(bpf_prog_free_security, selinux_bpf_prog_free),
 #endif
+
+#ifdef CONFIG_PERF_EVENTS
+	LSM_HOOK_INIT(perf_event_open, selinux_perf_event_open),
+	LSM_HOOK_INIT(perf_event_alloc, selinux_perf_event_alloc),
+	LSM_HOOK_INIT(perf_event_free, selinux_perf_event_free),
+	LSM_HOOK_INIT(perf_event_read, selinux_perf_event_read),
+	LSM_HOOK_INIT(perf_event_write, selinux_perf_event_write),
+#endif
 };
 
 static __init int selinux_init(void)