selftests: tpm2: Determine available PCR bank

Determine an available PCR bank to be used by a test case by querying the
capability TPM2_GET_CAP. The TPM2 returns TPML_PCR_SELECTIONS that
contains an array of TPMS_PCR_SELECTIONs indicating available PCR banks
and the bitmasks that show which PCRs are enabled in each bank. Collect
the data in a dictionary. From the dictionary determine the PCR bank that
has the PCRs enabled that the test needs. This avoids test failures with
TPM2's that either to not have a SHA-1 bank or whose SHA-1 bank is
disabled.

Signed-off-by: Stefan Berger <[e-mail]>
Tested-by: Jarkko Sakkinen <[e-mail]>
Reviewed-by: Jarkko Sakkinen <[e-mail]>
Signed-off-by: Jarkko Sakkinen <[e-mail]>

tools/testing/selftests/tpm2/tpm2.py

···
 
 TPM2_CAP_HANDLES = 0x00000001
 TPM2_CAP_COMMANDS = 0x00000002
+TPM2_CAP_PCRS = 0x00000005
 TPM2_CAP_TPM_PROPERTIES = 0x00000006
 
 TPM2_PT_FIXED = 0x100
···
             pt += 1
 
         return handles
+
+    def get_cap_pcrs(self):
+        pcr_banks = {}
+
+        fmt = '>HII III'
+
+        cmd = struct.pack(fmt,
+                          TPM2_ST_NO_SESSIONS,
+                          struct.calcsize(fmt),
+                          TPM2_CC_GET_CAPABILITY,
+                          TPM2_CAP_PCRS, 0, 1)
+        rsp = self.send_cmd(cmd)[10:]
+        _, _, cnt = struct.unpack('>BII', rsp[:9])
+        rsp = rsp[9:]
+
+        # items are TPMS_PCR_SELECTION's
+        for i in range(0, cnt):
+              hash, sizeOfSelect = struct.unpack('>HB', rsp[:3])
+              rsp = rsp[3:]
+
+              pcrSelect = 0
+              if sizeOfSelect > 0:
+                  pcrSelect, = struct.unpack('%ds' % sizeOfSelect,
+                                             rsp[:sizeOfSelect])
+                  rsp = rsp[sizeOfSelect:]
+                  pcrSelect = int.from_bytes(pcrSelect, byteorder='big')
+
+              pcr_banks[hash] = pcrSelect
+
+        return pcr_banks

tools/testing/selftests/tpm2/tpm2_tests.py

···
         result = self.client.unseal(self.root_key, blob, auth, None)
         self.assertEqual(data, result)
 
+    def determine_bank_alg(self, mask):
+        pcr_banks = self.client.get_cap_pcrs()
+        for bank_alg, pcrSelection in pcr_banks.items():
+            if pcrSelection & mask == mask:
+                return bank_alg
+        return None
+
     def test_seal_with_policy(self):
+        bank_alg = self.determine_bank_alg(1 << 16)
+        self.assertIsNotNone(bank_alg)
+
         handle = self.client.start_auth_session(tpm2.TPM2_SE_TRIAL)
 
         data = ('X' * 64).encode()
···
         pcrs = [16]
 
         try:
-            self.client.policy_pcr(handle, pcrs)
+            self.client.policy_pcr(handle, pcrs, bank_alg=bank_alg)
             self.client.policy_password(handle)
 
             policy_dig = self.client.get_policy_digest(handle)
···
         handle = self.client.start_auth_session(tpm2.TPM2_SE_POLICY)
 
         try:
-            self.client.policy_pcr(handle, pcrs)
+            self.client.policy_pcr(handle, pcrs, bank_alg=bank_alg)
             self.client.policy_password(handle)
 
             result = self.client.unseal(self.root_key, blob, auth, handle)
···
         self.assertEqual(rc, tpm2.TPM2_RC_AUTH_FAIL)
 
     def test_unseal_with_wrong_policy(self):
+        bank_alg = self.determine_bank_alg(1 << 16 | 1 << 1)
+        self.assertIsNotNone(bank_alg)
+
         handle = self.client.start_auth_session(tpm2.TPM2_SE_TRIAL)
 
         data = ('X' * 64).encode()
···
         pcrs = [16]
 
         try:
-            self.client.policy_pcr(handle, pcrs)
+            self.client.policy_pcr(handle, pcrs, bank_alg=bank_alg)
             self.client.policy_password(handle)
 
             policy_dig = self.client.get_policy_digest(handle)
···
         # Extend first a PCR that is not part of the policy and try to unseal.
         # This should succeed.
 
-        ds = tpm2.get_digest_size(tpm2.TPM2_ALG_SHA1)
-        self.client.extend_pcr(1, ('X' * ds).encode())
+        ds = tpm2.get_digest_size(bank_alg)
+        self.client.extend_pcr(1, ('X' * ds).encode(), bank_alg=bank_alg)
 
         handle = self.client.start_auth_session(tpm2.TPM2_SE_POLICY)
 
         try:
-            self.client.policy_pcr(handle, pcrs)
+            self.client.policy_pcr(handle, pcrs, bank_alg=bank_alg)
             self.client.policy_password(handle)
 
             result = self.client.unseal(self.root_key, blob, auth, handle)
···
 
         # Then, extend a PCR that is part of the policy and try to unseal.
         # This should fail.
-        self.client.extend_pcr(16, ('X' * ds).encode())
+        self.client.extend_pcr(16, ('X' * ds).encode(), bank_alg=bank_alg)
 
         handle = self.client.start_auth_session(tpm2.TPM2_SE_POLICY)
 
         rc = 0
 
         try:
-            self.client.policy_pcr(handle, pcrs)
+            self.client.policy_pcr(handle, pcrs, bank_alg=bank_alg)
             self.client.policy_password(handle)
 
             result = self.client.unseal(self.root_key, blob, auth, handle)