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KEYS: trusted: allow module init if TPM is inactive or deactivated

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Commit c78719203f ("KEYS: trusted: allow trusted.ko to initialize w/o a
TPM") allows the trusted module to be loaded even if a TPM is not found, to
avoid module dependency problems.

However, trusted module initialization can still fail if the TPM is
inactive or deactivated. tpm_get_random() returns an error.

This patch removes the call to tpm_get_random() and instead extends the PCR
specified by the user with zeros. The security of this alternative is
equivalent to the previous one, as either option prevents with a PCR update
unsealing and misuse of sealed data by a user space process.

Even if a PCR is extended with zeros, instead of random data, it is still
computationally infeasible to find a value as input for a new PCR extend
operation, to obtain again the PCR value that would allow unsealing.

Cc: stable@vger.kernel.org
Fixes: 240730437d ("KEYS: trusted: explicitly use tpm_chip structure...")
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Tyler Hicks <tyhicks@canonical.com>
Suggested-by: Mimi Zohar <zohar@linux.ibm.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
This commit is contained in:
Roberto Sassu 2019-08-05 18:44:27 +02:00 committed by Jarkko Sakkinen
parent d45331b00d
commit 2d6c25215a
1 changed files with 0 additions and 13 deletions
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13
security/keys/trusted.c
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@ -1228,24 +1228,11 @@ hashalg_fail:
static int __init init_digests(void)
{
u8 digest[TPM_MAX_DIGEST_SIZE];
int ret;
int i;
ret = tpm_get_random(chip, digest, TPM_MAX_DIGEST_SIZE);
if (ret < 0)
return ret;
if (ret < TPM_MAX_DIGEST_SIZE)
return -EFAULT;
digests = kcalloc(chip->nr_allocated_banks, sizeof(*digests),
GFP_KERNEL);
if (!digests)
return -ENOMEM;
for (i = 0; i < chip->nr_allocated_banks; i++)
memcpy(digests[i].digest, digest, TPM_MAX_DIGEST_SIZE);
return 0;
}