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

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Mon Nov 4, 2024 at 1:27 PM EET, Ard Biesheuvel wrote:
> On Mon, 4 Nov 2024 at 12:18, Jarkko Sakkinen <jarkko@kernel.org> 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.
> >
>
> Daniel has been nothing but courteous and patient, and you've waited
> 11 revision to come up with some bikeshedding patches that don't
> materially improve anything.
>
> So commenting on Daniel's approach here is uncalled for.
>
> Can we please converge on this?
>
> Daniel - if no component can be built as a module, there should be no
> reason for the set_default_locality() hook to be exported to modules
> right? And do we even need a sysfs node to expose this information?

I provided patches with my sob's and spent time on making the delta
absolute minimal to what exists already. If those are picked, I'm
good. They are essentially drop-in replicas to the existing patches.

BR, Jarkko