linux-kernel - [PATCH 1/2] ima: use the IMA configured hash algo to calculate the boot aggregate

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Message-Id: <1580140919-6127-1-git-send-email-zohar@linux.ibm.com>
Date:   Mon, 27 Jan 2020 11:01:58 -0500
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     linux-integrity@...r.kernel.org
Cc:     Jerry Snitselaar <jsnitsel@...hat.com>,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        linux-kernel@...r.kernel.org, Mimi Zohar <zohar@...ux.ibm.com>
Subject: [PATCH 1/2] ima: use the IMA configured hash algo to calculate the boot aggregate

The boot aggregate is a cumulative SHA1 hash over TPM registers 0 - 7.
NIST has depreciated the usage of SHA1 in most instances.  Instead of
continuing to use SHA1 to calculate the boot_aggregate, use the
configured IMA default hash algorithm.

Although the IMA measurement list boot_aggregate template data contains
the hash algorithm followed by the digest, allowing verifiers (e.g.
attesttaion servers) to calculate and verify the boot_aggregate, the
verifiers might not have the knowledge of what constitutes a good value
based on a different hash algorithm.

Signed-off-by: Mimi Zohar <zohar@...ux.ibm.com>
---
 security/integrity/ima/ima_init.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/security/integrity/ima/ima_init.c b/security/integrity/ima/ima_init.c
index 195cb4079b2b..b1b334fe0db5 100644
--- a/security/integrity/ima/ima_init.c
+++ b/security/integrity/ima/ima_init.c
@@ -27,7 +27,7 @@ struct tpm_chip *ima_tpm_chip;
 /* Add the boot aggregate to the IMA measurement list and extend
  * the PCR register.
  *
- * Calculate the boot aggregate, a SHA1 over tpm registers 0-7,
+ * Calculate the boot aggregate, a hash over tpm registers 0-7,
  * assuming a TPM chip exists, and zeroes if the TPM chip does not
  * exist.  Add the boot aggregate measurement to the measurement
  * list and extend the PCR register.
@@ -51,14 +51,14 @@ static int __init ima_add_boot_aggregate(void)
 	int violation = 0;
 	struct {
 		struct ima_digest_data hdr;
-		char digest[TPM_DIGEST_SIZE];
+		char digest[TPM_MAX_DIGEST_SIZE];
 	} hash;
 
 	memset(iint, 0, sizeof(*iint));
 	memset(&hash, 0, sizeof(hash));
 	iint->ima_hash = &hash.hdr;
-	iint->ima_hash->algo = HASH_ALGO_SHA1;
-	iint->ima_hash->length = SHA1_DIGEST_SIZE;
+	iint->ima_hash->algo = ima_hash_algo;
+	iint->ima_hash->length = hash_digest_size[ima_hash_algo];
 
 	if (ima_tpm_chip) {
 		result = ima_calc_boot_aggregate(&hash.hdr);
-- 
2.7.5