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

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Date: Tue, 21 May 2024 10:13:45 -0400
From: James Bottomley <James.Bottomley@...senPartnership.com>
To: Jarkko Sakkinen <jarkko@...nel.org>, 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, 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).

The spec has a mechanism for deriving the key from a permanent handle
if the system doesn't have it in-place.  I do have patches to use that
because that's the way most sealed objects and keys are generated
today.  I'll post them (although there'll be a bit of fixing up to do).

Regards,

James