Message-ID: <2557c1e2-b0fa-8729-0eb0-6ae68ee6f653@linux.ibm.com>
Date:   Fri, 26 Nov 2021 22:43:42 -0500
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Subject: Re: [PATCH v3 1/3] selftests: tpm2: Probe for available PCR bank
Content-Language: en-US
To:     Jarkko Sakkinen <jarkko@kernel.org>,
        Stefan Berger <stefanb@linux.vnet.ibm.com>,
        linux-integrity@vger.kernel.org
Cc:     peterhuewe@gmx.de, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org, skhan@linuxfoundation.org
References: <20211125003827.1360432-1-stefanb@linux.vnet.ibm.com>
 <20211125003827.1360432-2-stefanb@linux.vnet.ibm.com>
 <97ddf0f23592b74e7647e3c9b36b37553c594c82.camel@kernel.org>
From:   Stefan Berger <stefanb@linux.ibm.com>
In-Reply-To: <97ddf0f23592b74e7647e3c9b36b37553c594c82.camel@kernel.org>
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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@linux.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?

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@linux.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)