RE: [PATCH v3 7/8] ima: Calculate and extend PCR with digests in ima_template_entry

Roberto Sassu
2020-03-18T12:42:45Z

> -----Original Message-----
> From: owner-linux-security-module@vger.kernel.org [mailto:owner-linux-
> security-module@vger.kernel.org] On Behalf Of Mimi Zohar
> Sent: Tuesday, March 3, 2020 5:04 AM
> To: Roberto Sassu <roberto.sassu@huawei.com>;
> James.Bottomley@HansenPartnership.com;
> jarkko.sakkinen@linux.intel.com
> Cc: linux-integrity@vger.kernel.org; linux-security-module@vger.kernel.org;
> linux-kernel@vger.kernel.org; Silviu Vlasceanu
> <Silviu.Vlasceanu@huawei.com>
> Subject: Re: [PATCH v3 7/8] ima: Calculate and extend PCR with digests in
> ima_template_entry
>
> On Mon, 2020-02-10 at 11:04 +0100, Roberto Sassu wrote:
>
> > @@ -219,6 +214,8 @@ int ima_restore_measurement_entry(struct
> ima_template_entry *entry)
> >
> > int __init ima_init_digests(void)
> > {
> > + u16 digest_size;
> > + u16 crypto_id;
> > int i;
> >
> > if (!ima_tpm_chip)
> > @@ -229,8 +226,17 @@ int __init ima_init_digests(void)
> > if (!digests)
> > return -ENOMEM;
> >
> > - for (i = 0; i < ima_tpm_chip->nr_allocated_banks; i++)
> > + for (i = 0; i < ima_tpm_chip->nr_allocated_banks; i++) {
> > digests[i].alg_id = ima_tpm_chip->allocated_banks[i].alg_id;
> > + digest_size = ima_tpm_chip->allocated_banks[i].digest_size;
> > + crypto_id = ima_tpm_chip->allocated_banks[i].crypto_id;
> > +
> > + /* for unmapped TPM algorithms digest is still a padded
> SHA1 */
> > + if (crypto_id == HASH_ALGO__LAST)
> > + digest_size = SHA1_DIGEST_SIZE;
> > +
> > + memset(digests[i].digest, 0xff, digest_size);
>
> Shouldn't the memset here be of the actual digest size even for
> unmapped TPM algorithms.

This is consistent with ima_calc_field_array_hash(), so that a verifier
will always pad the SHA1 digest with zeros to obtain the final PCR value.

I can set all bytes if you prefer.

Thanks

Roberto

HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063
Managing Director: Li Peng, Li Jian, Shi Yanli

> > + }
> >
> > return 0;
> > }