linux-kernel - Re: [PATCH 1/3] tpm: protect against locality counter underflow

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Date: Tue, 20 Feb 2024 23:10:16 +0000
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: <ross.philipson@...cle.com>, "Lino Sanfilippo"
 <l.sanfilippo@...bus.com>, "Alexander Steffen"
 <Alexander.Steffen@...ineon.com>, "Daniel P. Smith"
 <dpsmith@...rtussolutions.com>, "Jason Gunthorpe" <jgg@...pe.ca>, "Sasha
 Levin" <sashal@...nel.org>, <linux-integrity@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>
Cc: "Kanth Ghatraju" <kanth.ghatraju@...cle.com>, "Peter Huewe"
 <peterhuewe@....de>
Subject: Re: [PATCH 1/3] tpm: protect against locality counter underflow

On Tue Feb 20, 2024 at 10:57 PM UTC,  wrote:
> On 2/20/24 2:26 PM, Jarkko Sakkinen wrote:
> > On Tue Feb 20, 2024 at 8:54 PM UTC, Lino Sanfilippo wrote:
> >> for (i = 0; i <= MAX_LOCALITY; i++)
> >> 	__tpm_tis_relinquish_locality(priv, i);
> > 
> > I'm pretty unfamiliar with Intel TXT so asking a dummy question:
> > if Intel TXT uses locality 2 I suppose we should not try to
> > relinquish it, or?
>
> The TPM has five localities (0 - 4). Localities 1 - 4 are for DRTM 
> support. For TXT, locality 4 is hard wired to the CPU - nothing else can 

Locality 4 is familiar because it comes across from time to time.

If I recall correctly DRTM should use only localities 3-4 and 
localities 0-2 should be reserved for the OS use.

So this does not match what I recall unfortunately but I'm not
really expert with this stuff.

The patches has zero explanations SINIT ACM's behaviour on
locality use and without that this cannot move forward because
there's neither way to reproduce any of this.

Actually there's zero effort on anything related to SINIT.

> an AC (Authenticated Code) module. That leaves 1 and 2 for the DRTM 
> software environment to use. If the DRTM software opens 1 or 2, it 
> should close them before exiting the DRTM.
>
> > 
> > AFAIK, we don't have a symbol called MAX_LOCALITY.
>
> Daniel added it in the patch set.

Got this, my symbol lookup just failed in my Git tree but looking at
the patch set there was a symbol called *TPM_*MAX_LOCALITY :-)

BR, Jarkko