From: "Jarkko Sakkinen" <jarkko@kernel.org>
To: "Daniel P. Smith" <dpsmith@apertussolutions.com>,
"James Bottomley" <James.Bottomley@HansenPartnership.com>,
"Lino Sanfilippo" <l.sanfilippo@kunbus.com>,
"Alexander Steffen" <Alexander.Steffen@infineon.com>,
"Jason Gunthorpe" <jgg@ziepe.ca>,
"Sasha Levin" <sashal@kernel.org>,
<linux-integrity@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Cc: "Ross Philipson" <ross.philipson@oracle.com>,
"Kanth Ghatraju" <kanth.ghatraju@oracle.com>,
"Peter Huewe" <peterhuewe@gmx.de>
Subject: Re: [PATCH 1/3] tpm: protect against locality counter underflow
Date: Fri, 23 Feb 2024 22:40:14 +0200 [thread overview]
Message-ID: <CZCQZ5FTCCB5.GIN1NU7G5S0@suppilovahvero> (raw)
In-Reply-To: <f1a54774-9a44-4400-91e2-358facc12191@apertussolutions.com>
On Fri Feb 23, 2024 at 3:57 AM EET, Daniel P. Smith wrote:
> On 2/21/24 14:43, 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.
> >
> > I was merely asking that if TPM_ACCESS_X is not properly cleared and you
> > se TPM_ACCESS_Y where Y < X how does the hardware react as the bug
> > report is pretty open ended and not very clear of the steps leading to
> > unwanted results.
> >
> > With a quick check from [1] could not spot the conflict reaction but
> > it is probably there.
>
> The expected behavior is explained in the Informative Comment of section
> 6.5.2.4 of the Client PTP spec[1]:
>
> "The purpose of this register is to allow the processes operating at the
> various localities to share the TPM. The basic notion is that any
> locality can request access to the TPM by setting the
> TPM_ACCESS_x.requestUse field using its assigned TPM_ACCESS_x register
> address. If there is no currently set locality, the TPM sets current
> locality to the requesting one and allows operations only from that
> locality. If the TPM is currently at another locality, the TPM keeps the
> request pending until the currently executing locality frees the TPM.
Right.
I'd think it would make sense to document the basic dance like this as
part of kdoc for request_locality:
* Setting TPM_ACCESS_x.requestUse:
* 1. No locality reserved => set locality.
* 2. Locality reserved => set pending.
I.e. easy reminder with enough granularity.
> Software relinquishes the TPM’s locality by writing a 1 to the
> TPM_ACCESS_x.activeLocality field. Upon release, the TPM honors the
> highest locality request pending. If there is no pending request, the
> TPM enters the “free” state."
And this for relinquish_locality:
* Setting TPM_ACCESS_x.activeLocality:
* 1. No locality pending => free.
* 2. Localities pending => reserve for highest.
> >> submission). I think the locality request/relinquish was modelled
> >> after some other HW, but I don't know what.
> >
> > My wild guess: first implementation was made when TPM's became available
> > and there was no analytical thinking other than getting something that
> > runs :-)
>
> Actually, no that is not how it was done. IIRC, localities were designed
> in conjunction with D-RTM when Intel and MS started the LeGrande effort
> back in 2000. It was then generalized for the TPM 1.1b specification. My
OK, thanks for this bit of information! I did not know this.
> first introduction to LeGrande/TXT wasn't until 2005 as part of an early
> access program. So most of my historical understanding is from
> discussions I luckily got to have with one of the architects and a few
> of the original TCG committee members.
Thanks alot for sharing this.
>
> [1]
> https://trustedcomputinggroup.org/wp-content/uploads/PC-Client-Specific-Platform-TPM-Profile-for-TPM-2p0-v1p05p_r14_pub.pdf
>
> v/r,
> dps
BR, Jarkko
next prev parent reply other threads:[~2024-02-23 20:40 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20240131170824.6183-1-dpsmith@apertussolutions.com>
2024-01-31 17:08 ` [PATCH 1/3] tpm: protect against locality counter underflow Daniel P. Smith
2024-02-01 22:21 ` Jarkko Sakkinen
2024-02-02 3:08 ` Lino Sanfilippo
2024-02-12 20:05 ` Jarkko Sakkinen
2024-02-19 17:54 ` Daniel P. Smith
2024-02-20 18:42 ` Alexander Steffen
2024-02-20 19:04 ` Jarkko Sakkinen
2024-02-20 20:54 ` Lino Sanfilippo
2024-02-20 22:23 ` Jarkko Sakkinen
2024-02-20 23:19 ` Lino Sanfilippo
2024-02-21 0:40 ` Jarkko Sakkinen
2024-02-23 1:58 ` Daniel P. Smith
2024-02-23 12:58 ` Jarkko Sakkinen
2024-02-25 11:23 ` Daniel P. Smith
2024-02-26 9:39 ` Jarkko Sakkinen
2024-02-20 22:26 ` Jarkko Sakkinen
2024-02-20 22:31 ` Jarkko Sakkinen
2024-02-20 23:26 ` Lino Sanfilippo
2024-02-21 0:42 ` Jarkko Sakkinen
2024-02-21 12:37 ` James Bottomley
2024-02-21 19:43 ` Jarkko Sakkinen
2024-02-21 19:45 ` Jarkko Sakkinen
2024-02-22 9:06 ` James Bottomley
2024-02-22 23:49 ` Jarkko Sakkinen
2024-02-23 1:57 ` Daniel P. Smith
2024-02-23 20:40 ` Jarkko Sakkinen [this message]
2024-02-23 20:42 ` Jarkko Sakkinen
2024-02-23 1:57 ` Daniel P. Smith
2024-02-23 20:50 ` Jarkko Sakkinen
2024-02-20 22:57 ` ross.philipson
2024-02-20 23:10 ` Jarkko Sakkinen
2024-02-20 23:13 ` Jarkko Sakkinen
2024-02-23 1:56 ` Daniel P. Smith
2024-02-23 20:44 ` Jarkko Sakkinen
2024-02-24 2:34 ` Lino Sanfilippo
2024-02-26 9:38 ` Jarkko Sakkinen
2024-02-23 1:55 ` Daniel P. Smith
2024-02-26 12:43 ` Alexander Steffen
2024-02-24 2:06 ` Lino Sanfilippo
2024-02-23 0:01 ` Jarkko Sakkinen
2024-01-31 17:08 ` [PATCH 2/3] tpm: ensure tpm is in known state at startup Daniel P. Smith
2024-02-01 22:33 ` Jarkko Sakkinen
2024-02-19 19:17 ` Daniel P. Smith
2024-02-19 20:17 ` Jarkko Sakkinen
2024-01-31 17:08 ` [PATCH 3/3] tpm: make locality request return value consistent Daniel P. Smith
2024-02-01 22:49 ` Jarkko Sakkinen
2024-02-19 20:29 ` Daniel P. Smith
2024-02-19 20:45 ` Jarkko Sakkinen
2024-02-20 18:57 ` Alexander Steffen
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