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

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Message-ID: <97ddf0f23592b74e7647e3c9b36b37553c594c82.camel@kernel.org>
Date:   Sat, 27 Nov 2021 02:29:00 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        linux-integrity@...r.kernel.org
Cc:     peterhuewe@....de, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, skhan@...uxfoundation.org,
        Stefan Berger <stefanb@...ux.ibm.com>
Subject: Re: [PATCH v3 1/3] selftests: tpm2: Probe for available PCR bank

On Wed, 2021-11-24 at 19:38 -0500, Stefan Berger wrote:
> From: Stefan Berger <stefanb@...ux.ibm.com>
> 
> Probe for an available PCR bank to accommodate devices that do not have a

What does "probing for an vailable PCR bank" even mean?

> 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.

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@...ux.ibm.com>
> ---
>  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)