private/boringssl_self_test.te

# System and vendor domains for BoringSSL self test binaries.
#
# For FIPS compliance, all processes linked against libcrypto perform a startup
# self test which computes a hash of the BoringSSL Crypto Module (BCM) and, at least once
# per device boot, also run a series of Known Answer Tests (KAT) to verify functionality.
#
# The KATs are expensive, and to ensure they are run as few times as possible, they
# are skipped if a marker file exists in /dev/boringssl/selftest whose name is
# the hash of the BCM that was computed earlier.  The files are zero length and their contents
# should never be read or written.  To avoid giving arbitrary processes access to /dev/boringssl
# to create these marker files, there are dedicated self test binaries which this policy
# gives access to and which are run during early-init.
#
# Due to build skew, the version of libcrypto in /vendor may have a different hash than
# the system one.  To cater for this there are vendor variants of the self test binaries
# which also have permission to write to the same files in /dev/boringssl.  In the case where
# vendor and system libcrypto have the same hash, there will be a race to create the file,
# but this is harmless.
#
# If the self tests fail, then the device should reboot into firmware and for this reason
# the system boringssl_self_test domain needs to be in coredomain.  As vendor domains
# are not allowed in coredomain, this means that the vendor self tests cannot trigger a
# reboot.  However every binary linked against the vendor libcrypto will abort on startup,
# so in practice the device will crash anyway in this unlikely scenario.

# System boringssl_self_test domain
type boringssl_self_test, domain, coredomain;
type boringssl_self_test_exec, system_file_type, exec_type, file_type;

# Vendor boringssl_self_test domain
type vendor_boringssl_self_test, domain;
type vendor_boringssl_self_test_exec, vendor_file_type, exec_type, file_type;

# Switch to boringssl_self_test security domain when running boringssl_self_test_exec
init_daemon_domain(boringssl_self_test)

# Switch to vendor_boringssl_self_test security domain when running vendor_boringssl_self_test_exec
init_daemon_domain(vendor_boringssl_self_test)

# Marker files, common to both domains, indicating KAT have been performed on a particular libcrypto
#
# The files are zero length so there is no issue if both vendor and system code
# try to create the same file simultaneously. One will succeed and the other will fail
# silently, i.e. still indicate success.  Similar harmless naming collisions will happen in the
# system domain e.g. when system and APEX copies of libcrypto are identical.
type boringssl_self_test_marker, file_type;

# Allow self test binaries to create/check for the existence of boringssl_self_test_marker files
allow { boringssl_self_test vendor_boringssl_self_test }
  boringssl_self_test_marker:file create_file_perms;
allow { boringssl_self_test vendor_boringssl_self_test }
  boringssl_self_test_marker:dir ra_dir_perms;

# Allow self test binaries to write their stdout/stderr messages to kmsg_debug
allow { boringssl_self_test vendor_boringssl_self_test }
  kmsg_debug_device:chr_file { w_file_perms getattr ioctl };

# No other process should be able to create marker files because their existence causes the
# boringssl KAT to be skipped.
neverallow {
  domain
  -vendor_boringssl_self_test
  -boringssl_self_test
  -init
  -vendor_init
} boringssl_self_test_marker:file no_rw_file_perms;

neverallow {
  domain
  -vendor_boringssl_self_test
  -boringssl_self_test
  -init
  -vendor_init
} boringssl_self_test_marker:dir write;