linux-kernel - Re: [RFC PATCH 0/4] Alternative TPM patches for Trenchboot

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Message-Id: <D5DCR279TZY5.1C7KRTFPGD3WU@kernel.org>
Date: Mon, 04 Nov 2024 13:19:55 +0200
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Jarkko Sakkinen" <jarkko@...nel.org>, "Daniel P. Smith"
 <dpsmith@...rtussolutions.com>
Cc: <x86@...nel.org>, "Ross Philipson" <ross.philipson@...cle.com>, "Ard
 Biesheuvel" <ardb@...nel.org>, "Thomas Gleixner" <tglx@...utronix.de>,
 "Peter Huewe" <peterhuewe@....de>, "Jason Gunthorpe" <jgg@...pe.ca>, "open
 list:TPM DEVICE DRIVER" <linux-integrity@...r.kernel.org>, "open list"
 <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/4] Alternative TPM patches for Trenchboot

On Mon Nov 4, 2024 at 1:18 PM EET, Jarkko Sakkinen wrote:
> On Mon Nov 4, 2024 at 12:57 PM EET, Daniel P. Smith wrote:
> > On 11/2/24 14:00, Jarkko Sakkinen wrote:
> > > On Sat Nov 2, 2024 at 5:22 PM EET, Jarkko Sakkinen wrote:
> > >> It is not really my problem but I'm also wondering how the
> > >> initialization order is managed. What if e.g. IMA happens to
> > >> initialize before slmodule?
> > > 
> > > The first obvious observation from Trenchboot implementation is that it
> > > is 9/10 times worst idea ever to have splitted root of trust. Here it
> > > is realized by an LKM for slmodule.
> >
> > First, there is no conflict between IMA and slmodule. With your change 
> > to make locality switching a one shot, the only issue would be if IMA 
> > were to run first and issue a locality switch to Locality 0, thus 
> > blocking slmodule from switching to Locality 2. As for PCR usage, IMA 
> > uses the SRTM PCRs, which are completely accessible under Locality 2.
>
> Just pointing out a possible problem (e.g. with  TPM2_PolicyLocality).
>
> > Honestly, a better path forward would be to revisit the issue that is
> > driving most of that logic existing, which is the lack of a TPM
> > interface code in the setup kernel. As a reminder, this issue is due to
> > the TPM maintainers position that the only TPM code in the kernel can be
> > the mainline driver. Which, unless something has changed, is impossible
> > to compile into the setup kernel due to its use of mainline kernel
> > constructs not present in the setup kernel.
>
> I don't categorically reject adding some code to early setup. We have
> some shared code EFI stub but you have to explain your changes
> proeprly. Getting rejection in some early version to some approach,
> and being still pissed about that years forward is not really way
> to go IMHO.

... and ignoring fixes that took me almost one day to fully get together
is neither.

These address the awful commit messages, tpm_tis-only filtering and not
allowing repetition in the calls.

BR, Jarkko