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

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Message-Id: <CZB0JWCZJVF1.17B3HJLTYVOWD@seitikki>
Date: Wed, 21 Feb 2024 19:45:10 +0000
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Jarkko Sakkinen" <jarkko@...nel.org>, "James Bottomley"
 <James.Bottomley@...senPartnership.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: "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 Wed Feb 21, 2024 at 7:43 PM UTC, Jarkko Sakkinen wrote:
> On Wed Feb 21, 2024 at 12:37 PM UTC, James Bottomley wrote:
> > On Tue, 2024-02-20 at 22:31 +0000, Jarkko Sakkinen wrote:
> > > 
> > > 2. Because localities are not too useful these days given TPM2's
> > >    policy mechanism
> >
> > Localitites are useful to the TPM2 policy mechanism.  When we get key
> > policy in the kernel it will give us a way to create TPM wrapped keys
> > that can only be unwrapped in the kernel if we run the kernel in a
> > different locality from userspace (I already have demo patches doing
> > this).
>
> Let's keep this discussion in scope, please.
>
> Removing useless code using registers that you might have some actually
> useful use is not wrong thing to do. It is better to look at things from
> clean slate when the time comes.
>
> > >  I cannot recall out of top of my head can
> > >    you have two localities open at same time.
> >
> > I think there's a misunderstanding about what localities are: they're
> > effectively an additional platform supplied tag to a command.  Each
> > command can therefore have one and only one locality.  The TPM doesn't
>
> Actually this was not unclear at all. I even read the chapters from
> Ariel Segall's yesterday as a refresher.

Refering to https://www.amazon.com/Trusted-Platform-Modules-Computing-Networks/dp/1849198934

SBR, Jarkko