linux-kernel - Re: [Linux-ima-devel] [PATCH v2 4/5] keys, trusted: modify arguments of tpm_pcr

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Date:   Tue, 30 May 2017 15:41:13 +0200
From:   Roberto Sassu <roberto.sassu@...wei.com>
To:     Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        <tpmdd-devel@...ts.sourceforge.net>
CC:     <linux-ima-devel@...ts.sourceforge.net>,
        <linux-security-module@...r.kernel.org>,
        <keyrings@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [Linux-ima-devel] [PATCH v2 4/5] keys, trusted: modify arguments
 of tpm_pcr_extend()

On 5/30/2017 2:06 PM, Mimi Zohar wrote:
> On Tue, 2017-05-30 at 09:36 +0200, Roberto Sassu wrote:
>> On 5/30/2017 5:35 AM, Mimi Zohar wrote:
>>> On Fri, 2017-05-05 at 16:21 +0200, Roberto Sassu wrote:
>>>> pcrlock() has been modified to pass the correct arguments
>>>> to tpm_pcr_extend(): the pointer of a tpm2_digest structure containing
>>>> a random value generated by tpm_get_random() and the size of the array (1).
>>>
>>> If the number of arguments is wrong, that means the patch that
>>> introduced the change is not bi-sect safe.  (This comment is
>>> applicable to patch 5/5 too.)
>>
>> Jarkko (the TPM driver maintainer) asked me to not introduce
>> a new function to pass multiple digests, but to modify
>> the parameters of tpm_pcr_extend().
>
> Since struct tpm2_digest is a static size, shouldn't we be able to
> compute the number of digests?

The length of 'hash' is not passed to tpm_pcr_extend().

The only way to avoid changing the number of parameters would
be to pass a buffer whose format is the same of the event log
format defined by TCG:

<algo count> <algo1 ID> <digest1> ... <algoN ID> <digestN>

Roberto

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