platform_system_sepolicy/private/gsid.te

# gsid - Manager for GSI Installation

type gsid, domain;
type gsid_exec, exec_type, file_type, system_file_type;
typeattribute gsid coredomain;

init_daemon_domain(gsid)

binder_use(gsid)
binder_service(gsid)
add_service(gsid, gsi_service)
set_prop(gsid, gsid_prop)

# Needed to create/delete device-mapper nodes, and read/write to them.
allow gsid dm_device:chr_file rw_file_perms;
allow gsid dm_device:blk_file rw_file_perms;
allow gsid self:global_capability_class_set sys_admin;
dontaudit gsid self:global_capability_class_set dac_override;

# libfiemap_writer uses sysfs to derive the bottom of a device-mapper stacking.
# This requires traversing /sys/block/dm-N/slaves/* and reading the list of
# file names.
allow gsid sysfs_dm:dir r_dir_perms;

# Needed to read fstab, which is used to validate that system verity does not
# use check_once_at_most for sdcard installs. (Note: proc_cmdline is needed
# to get the A/B slot suffix).
allow gsid proc_cmdline:file r_file_perms;
allow gsid sysfs_dt_firmware_android:dir r_dir_perms;
allow gsid sysfs_dt_firmware_android:file r_file_perms;

# Needed to stat /data/gsi/* and realpath on /dev/block/by-name/*
allow gsid block_device:dir r_dir_perms;

# liblp queries these block alignment properties.
allowxperm gsid { userdata_block_device sdcard_block_device }:blk_file ioctl {
  BLKIOMIN
  BLKALIGNOFF
};

# When installing images to an sdcard, gsid needs to be able to stat() the
# block device. gsid also calls realpath() to remove symlinks.
allow gsid mnt_media_rw_file:dir r_dir_perms;

# When installing images to an sdcard, gsid must bypass sdcardfs and install
# directly to vfat, which supports the FIBMAP ioctl.
allow gsid vfat:dir rw_dir_perms;
allow gsid vfat:file create_file_perms;
allow gsid sdcard_block_device:blk_file r_file_perms;
# This is needed for FIBMAP unfortunately. Oddly FIEMAP does not carry this
# requirement, but the kernel does not implement FIEMAP support for VFAT.
allow gsid self:global_capability_class_set sys_rawio;

# gsi_tool passes the system image over the adb connection, via stdin.
allow gsid adbd:fd use;
# Needed when running gsi_tool through "su root" rather than adb root.
allow gsid adbd:unix_stream_socket rw_socket_perms;

neverallow { domain -gsid -init } gsid_prop:property_service set;

# gsid needs to store images on /data, but cannot use file I/O. If it did, the
# underlying blocks would be encrypted, and we couldn't mount the GSI image in
# first-stage init. So instead of directly writing to /data, we:
#
#   1. fallocate a file large enough to hold the signed GSI
#   2. extract its block layout with FIEMAP
#   3. create a dm-linear device using the FIEMAP, targeting /dev/block/by-name/userdata
#   4. write system_gsi into that dm device
#
# To make this process work, we need to unwrap the device-mapper stacking for
# userdata to reach the underlying block device. To verify the result we use
# stat(), which requires read access.
allow gsid userdata_block_device:blk_file r_file_perms;

# gsid uses /metadata/gsi to communicate GSI boot information to first-stage
# init. It cannot use userdata since data cannot be decrypted during this
# stage.
#
# gsid uses /metadata/gsi to store three files:
#   install_status - A short string indicating whether a GSI image is bootable.
#   lp_metadata    - LpMetadata blob describing the block ranges on userdata
#                    where system_gsi resides.
#   booted         - An empty file that, if exists, indicates that a GSI is
#                    currently running.
#
allow gsid metadata_file:dir search;
allow gsid gsi_metadata_file:dir rw_dir_perms;
allow gsid gsi_metadata_file:file create_file_perms;

allow gsid gsi_data_file:dir rw_dir_perms;
allow gsid gsi_data_file:file create_file_perms;
allowxperm gsid gsi_data_file:file ioctl FS_IOC_FIEMAP;

neverallow {
    domain
    -init
    -gsid
    -fastbootd
    -vold
} gsi_metadata_file:dir *;

neverallow {
    domain
    -init
    -gsid
    -fastbootd
    -vold
} gsi_metadata_file:notdevfile_class_set ~{ relabelto getattr };

neverallow {
    domain
    -init
    -gsid
    -fastbootd
    -vold
} { gsi_data_file gsi_metadata_file }:notdevfile_class_set *;

neverallow {
    domain
    -gsid
    -init
} gsi_data_file:dir ~{ open create read getattr setattr search relabelto ioctl };

neverallow {
    domain
    -init
    -gsid
} gsi_data_file:dir *;

neverallow {
    domain
    -gsid
} gsi_data_file:notdevfile_class_set ~{ relabelto getattr };