lockdown: Lock down perf when in confidentiality mode

Disallow the use of certain perf facilities that might allow userspace to
access kernel data.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Matthew Garrett <mjg59@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Signed-off-by: James Morris <jmorris@namei.org>

kernel/events/core.c

@@ -10798,6 +10798,13 @@ SYSCALL_DEFINE5(perf_event_open,
 	    perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
 		return -EACCES;
 
+	err = security_locked_down(LOCKDOWN_PERF);
+	if (err && (attr.sample_type & PERF_SAMPLE_REGS_INTR))
+		/* REGS_INTR can leak data, lockdown must prevent this */
+		return err;
+
+	err = 0;
+
 	/*
 	 * In cgroup mode, the pid argument is used to pass the fd
 	 * opened to the cgroup directory in cgroupfs. The cpu argument