ear: remove min operations from policy

Make the policy logic simpler. Rather than using the min function
(which I'm not sure is even defined on TrustClaims) use short-circuiting
to only evaluate the rules for the platform that has TCB values defined.

I don't think there is any risk that the policy could be tricked into
evaluating the wrong rules, such as the sample ones.

Signed-off-by: Tobin Feldman-Fitzthum <[email protected]>

attestation-service/src/token/ear_default_policy.rego

@@ -14,60 +14,24 @@ import rego.v1
 # For the `executables` trust claim, the value 33 stands for
 # "Runtime memory includes executables, scripts, files, and/or
 #  objects which are not recognized."
-default sample_executables := 33
-
-default snp_executables := 33
-
-default tdx_executables := 33
-
-default az_snp_executables := 33
-
-default az_tdx_executables := 33
-
-default se_executables := 33
+default executables := 33
 
 # For the `hardware` trust claim, the value 97 stands for
 # "A Verifier does not recognize an Attester's hardware or
 #  firmware, but it should be recognized."
-default sample_hardware := 97
-
-default snp_hardware := 97
-
-default tdx_hardware := 97
-
-default az_snp_hardware := 97
-
-default az_tdx_hardware := 97
-
-default se_hardware := 97
+default hardware := 97
 
 # For the `configuration` trust claim the value 36 stands for
 # "Elements of the configuration relevant to security are
 #  unavailable to the Verifier."
-default sample_configuration := 36
-
-default snp_configuration := 36
-
-default tdx_configuration := 36
-
-default az_snp_configuration := 36
-
-default az_tdx_configuration := 36
-
-default se_configuration := 36
-
-executables := min({sample_executables, snp_executables, tdx_executables, az_snp_executables, az_tdx_executables, se_executables})
-
-hardware := min({sample_hardware, snp_hardware, tdx_hardware, az_snp_hardware, az_tdx_hardware, se_hardware})
-
-configuration := min({sample_configuration, snp_configuration, tdx_configuration, az_snp_configuration, az_tdx_configuration, se_configuration})
+default configuration := 36
 
 ##### Sample
 
 # For the `executables` trust claim, the value 3 stands for
 # "Only a recognized genuine set of approved executables have
 #  been loaded during the boot process."
-sample_executables := 3 if {
+executables := 3 if {
 	# The sample attester does not report any launch digest.
 	# This is an example of how a real platform might validate executables.
 	input.sample.launch_digest in data.reference.launch_digest
@@ -77,17 +41,17 @@ sample_executables := 3 if {
 # "An Attester has passed its hardware and/or firmware
 #  verifications needed to demonstrate that these are genuine/
 #  supported.
-sample_hardware := 2 if {
+hardware := 2 if {
 	input.sample.svn in data.reference.svn
 }
 
 ##### SNP
-snp_executables := 3 if {
+executables := 3 if {
 	# In the future, we might calculate this measurement here various components
 	input.snp.launch_measurement in data.reference.snp_launch_measurement
 }
 
-snp_hardware := 2 if {
+hardware := 2 if {
 	# Check the reported TCB to validate the ASP FW
 	input.snp.reported_tcb_bootloader in data.reference.snp_bootloader
 	input.snp.reported_tcb_microcode in data.reference.snp_microcode
@@ -99,7 +63,7 @@ snp_hardware := 2 if {
 # "The configuration is a known and approved config."
 #
 # For this, we compare all the configuration fields.
-snp_configuration := 2 if {
+configuration := 2 if {
 	input.snp.policy_debug_allowed == 0
 	input.snp.policy_migrate_ma == 0
 	input.snp.platform_smt_enabled in data.reference.snp_smt_enabled