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

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Message-Id: <D1FEC6TB7660.2XD9X21W46X7V@kernel.org>
Date: Tue, 21 May 2024 17:35:58 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Jarkko Sakkinen" <jarkko@...nel.org>, "James Bottomley"
 <James.Bottomley@...senPartnership.com>, <linux-integrity@...r.kernel.org>
Cc: <keyrings@...r.kernel.org>, "Peter Huewe" <peterhuewe@....de>, "Jason
 Gunthorpe" <jgg@...pe.ca>, "Mimi Zohar" <zohar@...ux.ibm.com>, "David
 Howells" <dhowells@...hat.com>, "Paul Moore" <paul@...l-moore.com>, "James
 Morris" <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>,
 <linux-kernel@...r.kernel.org>, <linux-security-module@...r.kernel.org>
Subject: Re: [PATCH] tpm: enable HMAC encryption for only x86-64 and aarch64

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