Re: [PATCH 1/3] tpm: Disable TCG_TPM2_HMAC by default

[Jarkko Sakkinen]

On Tue May 21, 2024 at 4:11 PM EEST, Jarkko Sakkinen wrote:
> On Tue May 21, 2024 at 4:00 PM EEST, Jarkko Sakkinen wrote:
> > On Tue May 21, 2024 at 3:33 PM EEST, James Bottomley wrote:
> > > On Tue, 2024-05-21 at 10:10 +0300, Jarkko Sakkinen wrote:
> > > > This benchmark could be done in user space using /dev/tpm0.
> > >
> > > Let's actually try that.  If you have the ibmtss installed, the command
> > > to time primary key generation from userspace on your tpm is
> > >
> > > time tsscreateprimary -hi n -ecc nistp256
> > >
> > >
> > > And just for chuckles and grins, try it in the owner hierarchy as well
> > > (sometimes slow TPMs cache this)
> > >
> > > time tsscreateprimary -hi o -ecc nistp256
> > >
> > > And if you have tpm2 tools, the above commands should be:
> > >
> > > time tpm2_createprimary -C n -G ecc256
> > > time tpm2_createprimary -C o -G ecc256
> >
> > Thanks, I definitely want to try these in my NUC7. I can try both
> > stacks and it is pretty good test machine because it is old'ish
> > and slow ;-)
> >
> > I'm also thinking differently than when I put out this pull request.
> > I honestly think that it must be weird use case to use TPM with
> > a machine that dies with a HMAC pipe. It makes no sense to me and
> > I think we should focus on common sense here.
> >
> > I could imagine one use case: pre-production hardware that is not
> > yet in ASIC. But in that case you would probably build your kernel
> > picking exactly the right options. I mean it is only a default
> > after all.
> >
> > I think we could add this:
> >
> > 	default X86 || ARM64
> >
> > This pretty covers the spectrum where HMAC does make sense by
> > default. We can always relax it but this does not really take
> > away the legit user base from the feature.
> >
> > It would be a huge bottleneck to make HMAC also opt-in because
> > the stuff it adds makes a lot of sense when build on top. E.g.
> > the asymmetric key patch set that I sent within early week was
> > made possible by all this great work that you've done.
> >
> > So yeah, I'd like to send the above Kconfig changes, but that
> > is all I want to do this at this point.
>
> Patch is out (lore link was not yet available):
>
> https://lkml.org/lkml/2024/5/21/583

Right also: TCG_TPM is neither default in x86 defconfig. So it would
require two switches turned on to get basic TPM support ongoing. So
yeah, I think we're in a sweet spot with above patch.

BR, Jarkko