dev devices with permissive boot: disable perf_event_paranoid
Some functionality based on eBPF attached to tracepoints (gpu memory
accounting and time-in-state) rely on newer devices running with
"disabled" perf_event_paranoid controls as a result of the kernel having
LSM hooks in the perf_event_open syscall instead. This is tested
for, and set up by init via the sys.init.perf_lsm_hooks sysprop.
Development devices that boot into permissive mode still want the
eBPF-based functionality to work, but end up with a paranoid value that
disallows the syscall, as the LSM hook test expects to observe a SELinux
denial (which doesn't happen due to permissiveness).
As a pragmatic way of achieving the paranoid value override, we pretend
that the hook test has succeeded if we detect permissive SELinux during
second-stage init. It'd be nicer if we had a sysprop to reflect the
device's on-boot status of SELinux, but it's not worth adding for this
case.
BYPASS_INCLUSIVE_LANGUAGE_REASON=technical term
Bug: 170674916
Tested: booted crosshatch-userdebug with permissive kernel cmdline,
confirmed that the log message from the new codepath was present
in logcat, sysprop is 1, and paranoid is -1.
Change-Id: I9df5da2076cdbd777d35e50e8cd7a483ec85e20a
diff --git a/init/security.cpp b/init/security.cpp
index 2450d65..ac784a3 100644
--- a/init/security.cpp
+++ b/init/security.cpp
@@ -19,6 +19,7 @@
#include <errno.h>
#include <fcntl.h>
#include <linux/perf_event.h>
+#include <selinux/selinux.h>
#include <sys/ioctl.h>
#include <sys/syscall.h>
#include <unistd.h>
@@ -222,6 +223,19 @@
// supporting kernels that precede the perf_event_open hooks (Android common
// kernels 4.4 and 4.9).
Result<void> TestPerfEventSelinuxAction(const BuiltinArguments&) {
+ // Special case: for *development devices* that boot with permissive
+ // SELinux, treat the LSM hooks as present for the effect of lowering the
+ // perf_event_paranoid sysctl. The sysprop is reused for pragmatic reasons,
+ // as there no existing way for init rules to check for permissive boot at
+ // the time of writing.
+ if (ALLOW_PERMISSIVE_SELINUX) {
+ if (!security_getenforce()) {
+ LOG(INFO) << "Permissive SELinux boot, forcing sys.init.perf_lsm_hooks to 1.";
+ SetProperty("sys.init.perf_lsm_hooks", "1");
+ return {};
+ }
+ }
+
// Use a trivial event that will be configured, but not started.
struct perf_event_attr pe = {
.type = PERF_TYPE_SOFTWARE,