public/hal_neverallows.te

# only HALs responsible for network hardware should have privileged
# network capabilities
neverallow {
  halserverdomain
  -hal_bluetooth_server
  -hal_can_controller_server
  -hal_wifi_server
  -hal_wifi_hostapd_server
  -hal_wifi_supplicant_server
  -hal_telephony_server
} self:global_capability_class_set { net_admin net_raw };

# Unless a HAL's job is to communicate over the network, or control network
# hardware, it should not be using network sockets.
# NOTE: HALs for automotive devices have an exemption from this rule because in
# a car it is common to have external modules and HALs need to communicate to
# those modules using network.  Using this exemption for non-automotive builds
# will result in CTS failure.
neverallow {
  halserverdomain
  -hal_automotive_socket_exemption
  -hal_can_controller_server
  -hal_tetheroffload_server
  -hal_wifi_server
  -hal_wifi_hostapd_server
  -hal_wifi_supplicant_server
  -hal_telephony_server
} domain:{ udp_socket rawip_socket } *;

neverallow {
  halserverdomain
  -hal_automotive_socket_exemption
  -hal_can_controller_server
  -hal_tetheroffload_server
  -hal_wifi_server
  -hal_wifi_hostapd_server
  -hal_wifi_supplicant_server
  -hal_telephony_server
} {
  domain
  userdebug_or_eng(`-su')
}:tcp_socket *;

###
# HALs are defined as an attribute and so a given domain could hypothetically
# have multiple HALs in it (or even all of them) with the subsequent policy of
# the domain comprised of the union of all the HALs.
#
# This is a problem because
# 1) Security sensitive components should only be accessed by specific HALs.
# 2) hwbinder_call and the restrictions it provides cannot be reasoned about in
#    the platform.
# 3) The platform cannot reason about defense in depth if there are
#    monolithic domains etc.
#
# As an example, hal_keymaster and hal_gatekeeper can access the TEE and while
# its OK for them to share a process its not OK with them to share processes
# with other hals.
#
# The following neverallow rules, in conjuntion with CTS tests, assert that
# these security principles are adhered to.
#
# Do not allow a hal to exec another process without a domain transition.
# TODO remove exemptions.
neverallow {
  halserverdomain
  -hal_dumpstate_server
  -hal_telephony_server
} { file_type fs_type }:file execute_no_trans;
# Do not allow a process other than init to transition into a HAL domain.
neverallow { domain -init } halserverdomain:process transition;
# Only allow transitioning to a domain by running its executable. Do not
# allow transitioning into a HAL domain by use of seclabel in an
# init.*.rc script.
neverallow * halserverdomain:process dyntransition;