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

Commit 5d2954af4e2a ("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: 72548132d299 ("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>

diff --git a/security/keys/trusted.c b/security/keys/trusted.c
index 9a94672e7adccff05901782c47a2473185e05831..ade69913106540e4e1918b88654a8914f3bbe29d 100644 (file)
--- a/security/keys/trusted.c
+++ b/security/keys/trusted.c
@@ -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;
 }