SELinux policy for Chrome OS

SELinux policy for Chrome OS lives here.

Directory structure:

platform2/sepolicy

|- policy SELinux policies live here. It contains sids, access vectors, mls, security classes, users, and roles definitions, type definitions, necessary macros for policy writing, and AVC rules.
- |- base sids, access vectors, mls, security classes, users, roles definitions. fs_use, and genfs definitions. fs_use defines context for different filesystems, e.g, devtmpfs -> u:object_r:device:s0, ext4 -> u:object_r:labeledfs:s0. genfscon defines file labels from the policy (so no need to xattr actual inode), mostly for procfs.
- |- chromeos All Chrome OS AVCs except for those in chromeos_base live here. Chrome OS file type definitions also live here.
  - |- te_macros Chrome OS-specific macros to write .te files, excluding those in policy/base or in shared.
  - |- attributes Chrome OS attributes.
  - |- file.te Chrome OS file labels.
  - |- **.te AVC rules for different domains.
- |- chromeos_base minijail, cros_init, and cros init script domains live here. Inside structure similar to chromeos.
- |- mask_only an NO-OP mask to make sure (base + mask_only) combined is a valid monotlithic policy.
|- file_contexts file labels on system image, stateful partition, devtmpfs, sysfs live here.
\- shared shared macros live here.