Re: [PATCH v3 1/3] selftests: tpm2: Probe for available PCR bank

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On 11/26/21 19:29, Jarkko Sakkinen wrote:
On Wed, 2021-11-24 at 19:38 -0500, Stefan Berger wrote:
From: Stefan Berger <stefanb@xxxxxxxxxxxxx>

Probe for an available PCR bank to accommodate devices that do not have a
What does "probing for an vailable PCR bank" even mean?

Checking ? Testing ? What's the difference to those words?



SHA-1 PCR bank or whose SHA-1 bank is deactivated. Use the bank that can
be used for the TPM2 commands, such as the SHA-256 bank.
This is incorrect, as the patch does not have code to query
available hash algorithms.

I am not sure I understand. The new function determines which PCR banks (SHA-1 or SHA-256) the subsequent tests can use. It tries to execute the policy_pcr command with the given hash bank algorithm (SHA-256 or SHA-1) and if it returns an UnknowPcrBankError it tries the next one in the list. It doesn't need to query available hash algorithms. A TPM 2 may support SHA 256 and yet its SHA 256 bank may be deactivate.

What the code does, and only does that, is to use SHA-256 as
a fallback when SHA-1 is not enabled.

/Jarkko


Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxxxxx>
---
  tools/testing/selftests/tpm2/tpm2_tests.py | 35 +++++++++++++++++-----
  1 file changed, 27 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/tpm2/tpm2_tests.py b/tools/testing/selftests/tpm2/tpm2_tests.py
index 9d764306887b..6b88ff0e47b9 100644
--- a/tools/testing/selftests/tpm2/tpm2_tests.py
+++ b/tools/testing/selftests/tpm2/tpm2_tests.py
@@ -27,7 +27,23 @@ class SmokeTest(unittest.TestCase):
          result = self.client.unseal(self.root_key, blob, auth, None)
          self.assertEqual(data, result)
+    def determine_bank_alg(self):
+        # Probe for available PCR bank
+        for bank_alg in [tpm2.TPM2_ALG_SHA1, tpm2.TPM2_ALG_SHA256]:
+            try:
+                handle = self.client.start_auth_session(tpm2.TPM2_SE_TRIAL)
+                self.client.policy_pcr(handle, [17], bank_alg=bank_alg)
+                return bank_alg
+            except tpm2.UnknownPCRBankError:
+                pass
+            finally:
+                self.client.flush_context(handle)
+        return None
+
      def test_seal_with_policy(self):
+        bank_alg = self.determine_bank_alg()
+        self.assertIsNotNone(bank_alg)
+
          handle = self.client.start_auth_session(tpm2.TPM2_SE_TRIAL)
         data = ('X' * 64).encode()
@@ -35,7 +51,7 @@ class SmokeTest(unittest.TestCase):
          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)
@@ -47,7 +63,7 @@ class SmokeTest(unittest.TestCase):
          handle = self.client.start_auth_session(tpm2.TPM2_SE_POLICY)
         try:
-            self.client.policy_pcr(handle, p"Use SHA-256 as a fallback crs)
+            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)
@@ -72,6 +88,9 @@ class SmokeTest(unittest.TestCase):
          self.assertEqual(rc, tpm2.TPM2_RC_AUTH_FAIL)
     def test_unseal_with_wrong_policy(self):
+        bank_alg = self.determine_bank_alg()
+        self.assertIsNotNone(bank_alg)
+
          handle = self.client.start_auth_session(tpm2.TPM2_SE_TRIAL)
         data = ('X' * 64).encode()
@@ -79,7 +98,7 @@ class SmokeTest(unittest.TestCase):
          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)
@@ -91,13 +110,13 @@ class SmokeTest(unittest.TestCase):
          # 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)
@@ -109,14 +128,14 @@ class SmokeTest(unittest.TestCase):
         # 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)



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