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

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Date:   Wed, 24 Jun 2020 18:33:45 -0300
From:   Bruno Meneguele <bmeneg@...hat.com>
To:     Stefan Berger <stefanb@...ux.ibm.com>
Cc:     Maurizio Drocco <maurizio.drocco@....com>, zohar@...ux.ibm.com,
        Silviu.Vlasceanu@...wei.com, dmitry.kasatkin@...il.com,
        jejb@...ux.ibm.com, jmorris@...ei.org,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, mdrocco@...ux.vnet.ibm.com,
        roberto.sassu@...wei.com, serge@...lyn.com
Subject: Re: [PATCH v2] ima_evm_utils: extended calc_bootaggr to PCRs 8 - 9

On Wed, Jun 24, 2020 at 05:17:52PM -0400, Stefan Berger wrote:
> 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@....com>
> > > 
> > > 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?
> 

boot_aggregate in kernel, after the following patch be applied:

https://lkml.org/lkml/2020/6/23/833

is calculated regardless PCR 8 & 9 being zero or not.
Thus evmctl is only reflecting the same behavior.

I think it would be worth changing the commit log here.

> 
>    Stefan
> 
> 
> > > 
> > > Signed-off-by: Maurizio Drocco <maurizio.drocco@....com>
> > > ---
> > > 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@...hat.com>
> > 
> 

-- 
bmeneg 
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