[PATCH v3] KEYS: trusted: allow module init if TPM is inactive or deactivated

From: Roberto Sassu
Date: Mon Aug 05 2019 - 12:48:29 EST

Commit c78719203fc6 ("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.

Fixes: 240730437deb ("KEYS: trusted: explicitly use tpm_chip structure...")
Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
Reviewed-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxx>
Suggested-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
security/keys/trusted.c | 13 -------------
1 file changed, 13 deletions(-)

diff --git a/security/keys/trusted.c b/security/keys/trusted.c
index 9a94672e7adc..ade699131065 100644
--- a/security/keys/trusted.c
+++ b/security/keys/trusted.c
@@ -1228,24 +1228,11 @@ static int __init trusted_shash_alloc(void)

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),
if (!digests)
return -ENOMEM;

- for (i = 0; i < chip->nr_allocated_banks; i++)
- memcpy(digests[i].digest, digest, TPM_MAX_DIGEST_SIZE);
return 0;