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

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Message-ID: <20200127204941.2ewman4y5nzvkjqe@cantor>
Date:   Mon, 27 Jan 2020 13:49:41 -0700
From:   Jerry Snitselaar <jsnitsel@...hat.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] ima: use the IMA configured hash algo to calculate
 the boot aggregate

On Mon Jan 27 20, Mimi Zohar wrote:
>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
>

Tested the patches on the Dell and no longer spits out the error messages on boot.
/sys/kernel/security/ima/ascii_runtime_measurements shows the boot aggregate.

Is there something else I should look at to verify it is functioning properly?

Regards,
Jerry