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

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Date: Tue, 20 Feb 2024 22:31:23 +0000
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Jarkko Sakkinen" <jarkko@...nel.org>, "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: "Ross Philipson" <ross.philipson@...cle.com>, "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 10:26 PM UTC, 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?
>
> AFAIK, we don't have a symbol called MAX_LOCALITY.

OK it was called TPM_MAX_LOCALITY :-) I had the patch set applied
in one branch but looked up with wrong symbol name.

So I reformalize my question to two parts:

1. Why does TXT leave locality 2 open in the first place? I did
   not see explanation. Isn't this a bug in TXT?
2. Because localities are not too useful these days given TPM2's
   policy mechanism I cannot recall out of top of my head can
   you have two localities open at same time. So what kind of
   conflict happens when you try to open locality 0 and have
   locality 2 open?

BR, Jarkko