Re: [PATCH] tpm: enable HMAC encryption for only x86-64 and aarch64

[Jarkko Sakkinen]

On Tue May 21, 2024 at 5:26 PM EEST, Jarkko Sakkinen wrote:
> On Tue May 21, 2024 at 5:13 PM EEST, James Bottomley wrote:
> > On Tue, 2024-05-21 at 17:02 +0300, Jarkko Sakkinen wrote:
> > > Secondly, it also roots to the null key if a parent is not given. So
> > > it covers all the basic features of the HMAC patch set.
> >
> > I don't think that can work.  The key file would be wrapped to the
> > parent and the null seed (and hence the wrapping) changes with every
> > reboot.  If you want a permanent key, it has to be in one of the
> > accessible permanent hierarchies (storage ideally or endorsement).
>
> I'm fully aware that null seed is randomized per power cycle.
>
> The fallback was inherited from James Prestwood's original code and I
> decided to keep it as a testing feature, and also to test HMAC changes.
>
> If you look at the testing transcript in the cover letter, it should be
> obvious that a primary key is created in my basic test.

I think what could be done to it in v3 would be to return -EOPNOTSUPP
if parent is not defined. I.e. rationale here is that this way the
empty option is still usable for something in future kernel releases.

BR, Jarkko