tpm: retrieve digest size of unknown algorithms with PCR read

Currently, the TPM driver retrieves the digest size from a table mapping
TPM algorithms identifiers to identifiers defined by the crypto subsystem.
If the algorithm is not defined by the latter, the digest size can be
retrieved from the output of the PCR read command.

The patch modifies the definition of tpm_pcr_read() and tpm2_pcr_read() to
pass the desired hash algorithm and obtain the digest size at TPM startup.
Algorithms and corresponding digest sizes are stored in the new structure
tpm_bank_info, member of tpm_chip, so that the information can be used by
other kernel subsystems.

tpm_bank_info contains: the TPM algorithm identifier, necessary to generate
the event log as defined by Trusted Computing Group (TCG); the digest size,
to pad/truncate a digest calculated with a different algorithm; the crypto
subsystem identifier, to calculate the digest of event data.

This patch also protects against data corruption that could happen in the
bus, by checking that the digest size returned by the TPM during a PCR read
matches the size of the algorithm passed to tpm2_pcr_read().

For the initial PCR read, when digest sizes are not yet available, this
patch ensures that the amount of data copied from the output returned by
the TPM does not exceed the size of the array data are copied to.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Acked-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 9fe8c9816cf0..afd022fc9d3d 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -47,6 +47,12 @@ struct tpm_digest {
 	u8 digest[TPM_MAX_DIGEST_SIZE];
 } __packed;
 
+struct tpm_bank_info {
+	u16 alg_id;
+	u16 digest_size;
+	u16 crypto_id;
+};
+
 enum TPM_OPS_FLAGS {
 	TPM_OPS_AUTO_STARTUP = BIT(0),
 };
@@ -72,7 +78,8 @@ struct tpm_class_ops {
 #if defined(CONFIG_TCG_TPM) || defined(CONFIG_TCG_TPM_MODULE)
 
 extern int tpm_is_tpm2(struct tpm_chip *chip);
-extern int tpm_pcr_read(struct tpm_chip *chip, u32 pcr_idx, u8 *res_buf);
+extern int tpm_pcr_read(struct tpm_chip *chip, u32 pcr_idx,
+			struct tpm_digest *digest);
 extern int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, const u8 *hash);
 extern int tpm_send(struct tpm_chip *chip, void *cmd, size_t buflen);
 extern int tpm_get_random(struct tpm_chip *chip, u8 *data, size_t max);
@@ -89,7 +96,8 @@ static inline int tpm_is_tpm2(struct tpm_chip *chip)
 	return -ENODEV;
 }
 
-static inline int tpm_pcr_read(struct tpm_chip *chip, u32 pcr_idx, u8 *res_buf)
+static inline int tpm_pcr_read(struct tpm_chip *chip, int pcr_idx,
+			       struct tpm_digest *digest)
 {
 	return -ENODEV;
 }