linux-kernel - Re: [PATCH v5 7/7] tpm: pass an array of tpm_bank_list structures to tpm_pcr

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Date:   Sun, 18 Nov 2018 09:27:45 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>
Cc:     zohar@...ux.ibm.com, david.safford@...com, monty.wiseman@...com,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, silviu.vlasceanu@...wei.com
Subject: Re: [PATCH v5 7/7] tpm: pass an array of tpm_bank_list structures to
 tpm_pcr_extend()

On Fri, Nov 16, 2018 at 04:55:36PM +0100, Roberto Sassu wrote:
> On 11/16/2018 4:03 PM, Jarkko Sakkinen wrote:
> > On Wed, Nov 14, 2018 at 04:31:08PM +0100, Roberto Sassu wrote:
> > > Currently, tpm_pcr_extend() accepts as an input only a SHA1 digest.
> > > 
> > > This patch modifies the definition of tpm_pcr_extend() to allow other
> > > kernel subsystems to pass a digest for each algorithm supported by the TPM.
> > > All digests are processed by the TPM in one operation.
> > > 
> > > If a tpm_pcr_extend() caller provides a subset of the supported algorithms,
> > > the TPM driver extends the remaining PCR banks with the first digest
> > > passed as an argument to the function.
> > 
> > What is the legit use case for this?
> 
> A subset could be chosen for better performance, or when a TPM algorithm
> is not supported by the crypto subsystem.

Doesn't extending a subset a security concern?

/Jarkko