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

[Roberto Sassu]

> -----Original Message-----
> From: owner-linux-security-module@xxxxxxxxxxxxxxx [mailto:owner-linux-
> security-module@xxxxxxxxxxxxxxx] On Behalf Of Mimi Zohar
> Sent: Tuesday, March 3, 2020 5:04 AM
> To: Roberto Sassu <roberto.sassu@xxxxxxxxxx>;
> James.Bottomley@xxxxxxxxxxxxxxxxxxxxx;
> jarkko.sakkinen@xxxxxxxxxxxxxxx
> Cc: linux-integrity@xxxxxxxxxxxxxxx; linux-security-module@xxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; Silviu Vlasceanu
> <Silviu.Vlasceanu@xxxxxxxxxx>
> 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;
> >  }