Re: [PATCH v2] ima_evm_utils: extended calc_bootaggr to PCRs 8 - 9

[Stefan Berger]

On 6/23/20 2:13 PM, Bruno Meneguele wrote:
> On Tue, Jun 23, 2020 at 02:01:22PM -0400, Maurizio Drocco wrote:
> > From: Maurizio <maurizio.drocco@xxxxxxx>
> >
> > If PCRs 8 - 9 are set (i.e. not all-zeros), cal_bootaggr should include
> > them into the digest.


Wouldn't you have to check for not all-zeros in your code?


   Stefan


> > Signed-off-by: Maurizio Drocco <maurizio.drocco@xxxxxxx>
> > ---
> > Changelog:
> > v2:
> > - Always include PCRs 8 & 9 to non-sha1 hashes
> > v1:
> > - Include non-zero PCRs 8 & 9 to boot aggregates
> >
> >   src/evmctl.c | 15 +++++++++++++--
> >   1 file changed, 13 insertions(+), 2 deletions(-)
> >
> > diff --git a/src/evmctl.c b/src/evmctl.c
> > index 1d065ce..46b7092 100644
> > --- a/src/evmctl.c
> > +++ b/src/evmctl.c
> > @@ -1930,6 +1930,16 @@ static void calc_bootaggr(struct tpm_bank_info *bank)
> >   		}
> >   	}
> >   
> > +	if (strcmp(bank->algo_name, "sha1") != 0) {
> > +		for (i = 8; i < 10; i++) {
> > +			err = EVP_DigestUpdate(pctx, bank->pcr[i], bank->digest_size);
> > +			if (!err) {
> > +				log_err("EVP_DigestUpdate() failed\n");
> > +				return;
> > +			}
> > +		}
> > +	}
> > +
> >   	err = EVP_DigestFinal(pctx, bank->digest, &mdlen);
> >   	if (!err) {
> >   		log_err("EVP_DigestFinal() failed\n");
> > @@ -1972,8 +1982,9 @@ static int append_bootaggr(char *bootaggr, struct tpm_bank_info *tpm_banks)
> >   /*
> >    * The IMA measurement list boot_aggregate is the link between the preboot
> >    * event log and the IMA measurement list.  Read and calculate all the
> > - * possible per TPM bank boot_aggregate digests based on the existing
> > - * PCRs 0 - 7 to validate against the IMA boot_aggregate record.
> > + * possible per TPM bank boot_aggregate digests based on the existing PCRs
> > + * 0 - 9 to validate against the IMA boot_aggregate record. If the digest
> > + * algorithm is SHA1, only PCRs 0 - 7 are considered to avoid ambiguity.
> >    */
> >   static int cmd_ima_bootaggr(struct command *cmd)
> >   {
> > --
> > 2.17.1
> Reviewed-by: Bruno Meneguele <bmeneg@xxxxxxxxxx>