linux-kernel - Re: [PATCH] extend IMA boot_aggregate with kernel measurements

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Date:   Thu, 11 Jun 2020 20:29:55 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Maurizio Drocco <maurizio.drocco@....com>,
        linux-integrity@...r.kernel.org
Cc:     jejb@...ux.ibm.com, Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        "open list:SECURITY SUBSYSTEM" 
        <linux-security-module@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] extend IMA boot_aggregate with kernel measurements

Hi Maurizo,

On Thu, 2020-06-11 at 15:54 -0400, Maurizio Drocco wrote:
> IMA is not considering TPM registers 8-9 when calculating the boot
> aggregate. When registers 8-9 are used to store measurements of the
> kernel and its command line (e.g., grub2 bootloader with tpm module
> enabled), IMA should include them in the boot aggregate.
> 
> Signed-off-by: Maurizio Drocco <maurizio.drocco@....com>

Looks good.  Just a minor comment below.  Could you be a bit more
specific as to what is being measured into which PCR.  Perhaps include
a reference to some doc or spec.

In order to test, ima-evm-utils needs to be updated as well.  Could
you post the corresponding evmctl change?  Please post the patch
against the ima-evm-utils next-testing branch.

> ---
>  security/integrity/ima/ima.h        |  2 +-
>  security/integrity/ima/ima_crypto.c | 11 ++++++++++-
>  2 files changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/security/integrity/ima/ima.h b/security/integrity/ima/ima.h
> index df93ac258e01..9d94080bdad8 100644
> --- a/security/integrity/ima/ima.h
> +++ b/security/integrity/ima/ima.h
> @@ -30,7 +30,7 @@
>  
>  enum ima_show_type { IMA_SHOW_BINARY, IMA_SHOW_BINARY_NO_FIELD_LEN,
>  		     IMA_SHOW_BINARY_OLD_STRING_FMT, IMA_SHOW_ASCII };
> -enum tpm_pcrs { TPM_PCR0 = 0, TPM_PCR8 = 8 };
> +enum tpm_pcrs { TPM_PCR0 = 0, TPM_PCR8 = 8, TPM_PCR10 = 10 };
>  
>  /* digest size for IMA, fits SHA1 or MD5 */
>  #define IMA_DIGEST_SIZE		SHA1_DIGEST_SIZE
> diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
> index 220b14920c37..6f0137bdaf61 100644
> --- a/security/integrity/ima/ima_crypto.c
> +++ b/security/integrity/ima/ima_crypto.c
> @@ -809,7 +809,7 @@ static void ima_pcrread(u32 idx, struct tpm_digest *d)
>  static int ima_calc_boot_aggregate_tfm(char *digest, u16 alg_id,
>  				       struct crypto_shash *tfm)
>  {
> -	struct tpm_digest d = { .alg_id = alg_id, .digest = {0} };
> +	struct tpm_digest d = { .alg_id = alg_id, .digest = {0} }, d0 = d;
>  	int rc;
>  	u32 i;
>  	SHASH_DESC_ON_STACK(shash, tfm);
> @@ -830,6 +830,15 @@ static int ima_calc_boot_aggregate_tfm(char *digest, u16 alg_id,
>  		rc = crypto_shash_update(shash, d.digest,
>  					 crypto_shash_digestsize(tfm));
>  	}
> +	/* extend cumulative sha1 over tpm registers 8-9 */
> +	for (i = TPM_PCR8; i < TPM_PCR10; i++) {
> +		ima_pcrread(i, &d);
> +		/* if not zero, accumulate with current aggregate */
> +		if (memcmp(d.digest, d0.digest,
> +					crypto_shash_digestsize(tfm) != 0))

The formatting here is a bit off.

thanks,

Mimi

> +			rc = crypto_shash_update(shash, d.digest,
> +					crypto_shash_digestsize(tfm));
> +	}
>  	if (!rc)
>  		crypto_shash_final(shash, digest);
>  	return rc;