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

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Date:   Tue, 3 Jan 2023 12:42:19 -0800
From:   Matthew Garrett <mgarrett@...ora.tech>
To:     jejb@...ux.ibm.com
Cc:     Evan Green <evgreen@...omium.org>, linux-kernel@...r.kernel.org,
        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, 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 Mon, Nov 14, 2022 at 9:11 AM James Bottomley <jejb@...ux.ibm.com> wrote:
>
> 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.

Is there any way to get key creation data to include NV indexes? If
not, no, we can't use NVRAM.