tracefs: avoid overly generic regexes
On boot, Android runs restorecon on a number of virtual directories,
such as /sys and /sys/kernel/debug, to ensure that the SELinux labels
are correct. To avoid causing excessive boot time delays, the restorecon
code aggressively prunes directories, to avoid recursing down directory
trees which will never have a matching SELinux label.
See:
* https://android-review.googlesource.com/93401
* https://android-review.googlesource.com/109103
The key to this optimization is avoiding unnecessarily broad regular
expressions in file_contexts. If an overly broad regex exists, the tree
pruning code is ineffective, and the restorecon ends up visiting lots of
unnecessary directories.
The directory /sys/kernel/debug/tracing contains approximately 4500
files normally, and on debuggable builds, this number can jump to over
9000 files when the processing from wifi-events.rc occurs. For
comparison, the entire /sys/kernel/debug tree (excluding
/sys/kernel/debug/tracing) only contains approximately 8000 files. The
regular expression "/sys/kernel(/debug)?/tracing/(.*)?" ends up matching
a significant number of files, which impacts boot performance.
Instead of using an overly broad regex, refine the regex so only the
files needed have an entry in file_contexts. This list of files is
essentially a duplicate of the entries in
frameworks/native/cmds/atrace/atrace.rc .
This change reduces the restorecon_recursive call for /sys/kernel/debug
from approximately 260ms to 40ms, a boot time reduction of approximately
220ms.
Bug: 35248779
Test: device boots, no SELinux denials, faster boot.
Change-Id: I70f8af102762ec0180546b05fcf014c097135f3e
diff --git a/private/file_contexts b/private/file_contexts
index 71f1586..812ae5a 100644
--- a/private/file_contexts
+++ b/private/file_contexts
@@ -445,12 +445,39 @@
# debugfs files
#
/sys/kernel/debug/mmc0(/.*)? u:object_r:debugfs_mmc:s0
-/sys/kernel(/debug)?/tracing/(.*)? u:object_r:debugfs_tracing:s0
-/sys/kernel(/debug)?/tracing/trace_marker u:object_r:debugfs_trace_marker:s0
-/sys/kernel(/debug)?/tracing/instances(/.*)? u:object_r:debugfs_tracing_instances:s0
-/sys/kernel(/debug)?/tracing/instances/wifi/free_buffer u:object_r:debugfs_wifi_tracing:s0
-/sys/kernel(/debug)?/tracing/instances/wifi/trace u:object_r:debugfs_wifi_tracing:s0
-/sys/kernel(/debug)?/tracing/instances/wifi/tracing_on u:object_r:debugfs_wifi_tracing:s0
+
+#############################
+# tracefs files
+#
+/sys/kernel(/debug)?/tracing/buffer_size_kb u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/binder/binder_locked/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/binder/binder_lock/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/binder/binder_transaction/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/binder/binder_transaction_received/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/binder/binder_unlock/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/cpufreq_interactive/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/power/clock_set_rate/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/power/cpu_frequency/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/power/cpu_frequency_limits/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/power/cpu_idle/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/sched/sched_blocked_reason/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/sched/sched_cpu_hotplug/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/sched/sched_switch/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/sched/sched_wakeup/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/vmscan/mm_vmscan_direct_reclaim_begin/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/vmscan/mm_vmscan_direct_reclaim_end/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/vmscan/mm_vmscan_kswapd_sleep/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/events/vmscan/mm_vmscan_kswapd_wake/enable u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/instances(/.*)? u:object_r:debugfs_tracing_instances:s0
+/sys/kernel(/debug)?/tracing/instances/wifi/free_buffer u:object_r:debugfs_wifi_tracing:s0
+/sys/kernel(/debug)?/tracing/instances/wifi/trace u:object_r:debugfs_wifi_tracing:s0
+/sys/kernel(/debug)?/tracing/instances/wifi/tracing_on u:object_r:debugfs_wifi_tracing:s0
+/sys/kernel(/debug)?/tracing/options/overwrite u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/options/print-tgid u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/trace u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/trace_clock u:object_r:tracing_shell_writable:s0
+/sys/kernel(/debug)?/tracing/trace_marker u:object_r:debugfs_trace_marker:s0
+/sys/kernel(/debug)?/tracing/tracing_on u:object_r:tracing_shell_writable:s0
#############################
# asec containers
diff --git a/private/shell.te b/private/shell.te
index 333265f..1e77964 100644
--- a/private/shell.te
+++ b/private/shell.te
@@ -1,6 +1,7 @@
# systrace support - allow atrace to run
allow shell debugfs_tracing:dir r_dir_perms;
-allow shell debugfs_tracing:file rw_file_perms;
+allow shell debugfs_tracing:file r_file_perms;
+allow shell tracing_shell_writable:file rw_file_perms;
allow shell debugfs_trace_marker:file getattr;
allow shell atrace_exec:file rx_file_perms;