linux-kernel - Re: [PATCH v5 03/11] tpm: Allow PCR 23 to be restricted to kernel-only use

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Message-ID: <8ae56656a461d7b957b93778d716c6161070383a.camel@linux.ibm.com>
Date:   Mon, 14 Nov 2022 12:11:20 -0500
From:   James Bottomley <jejb@...ux.ibm.com>
To:     Evan Green <evgreen@...omium.org>, linux-kernel@...r.kernel.org
Cc:     corbet@....net, linux-integrity@...r.kernel.org,
        Eric Biggers <ebiggers@...nel.org>, gwendal@...omium.org,
        dianders@...omium.org, apronin@...omium.org,
        Pavel Machek <pavel@....cz>, Ben Boeckel <me@...boeckel.net>,
        rjw@...ysocki.net, Kees Cook <keescook@...omium.org>,
        dlunev@...gle.com, zohar@...ux.ibm.com,
        Matthew Garrett <mgarrett@...ora.tech>, jarkko@...nel.org,
        linux-pm@...r.kernel.org, Matthew Garrett <mjg59@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>, Peter Huewe <peterhuewe@....de>
Subject: Re: [PATCH v5 03/11] tpm: Allow PCR 23 to be restricted to
 kernel-only use

On Fri, 2022-11-11 at 15:16 -0800, Evan Green wrote:
> Introduce a new Kconfig, TCG_TPM_RESTRICT_PCR, which if enabled
> restricts usermode's ability to extend or reset PCR 23.

Could I re ask the question here that I asked of Matthew's patch set:

https://lore.kernel.org/all/b0c4980c8fad14115daa3040979c52f07f7fbe2c.camel@linux.ibm.com/

Which was could we use an NVRAM index in the TPM instead of a PCR?  The
reason for asking was that PCRs are rather precious and might get more
so now that Lennart has some grand scheme for using more of them in his
unified boot project.  Matthew promised to play with the idea but never
got back to the patch set to say whether he investigated this or not.

James