linux-kernel - Re: [RFC PATCH 0/2] TPM derived keys

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Date: Tue, 14 May 2024 17:30:51 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Jarkko Sakkinen" <jarkko@...nel.org>, "Ignat Korchagin"
 <ignat@...udflare.com>
Cc: "James Bottomley" <James.Bottomley@...senpartnership.com>, "Mimi Zohar"
 <zohar@...ux.ibm.com>, "David Howells" <dhowells@...hat.com>, "Paul Moore"
 <paul@...l-moore.com>, "James Morris" <jmorris@...ei.org>,
 <serge@...lyn.com>, <linux-integrity@...r.kernel.org>,
 <keyrings@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <kernel-team@...udflare.com>
Subject: Re: [RFC PATCH 0/2] TPM derived keys

On Tue May 14, 2024 at 5:00 PM EEST, Jarkko Sakkinen wrote:
> On Tue May 14, 2024 at 4:11 PM EEST, Ignat Korchagin wrote:
> > For example, a cheap NAS box with no internal storage (disks connected
> > externally via USB). We want:
> >   * disks to be encrypted and decryptable only by this NAS box
>
> So how this differs from LUKS2 style, which also systemd supports where
> the encryption key is anchored to PCR's? If I took hard drive out of my
> Linux box, I could not decrypt it in another machine because of this.

Maybe you could replace the real LUKS2 header with a dummy LUKS2
header, which would need to be able the describe "do not use this" and
e.g. SHA256 of the actual header. And then treat the looked up header as
the header when the drive is mounted.

LUKS2 would also need to be able to have pre-defined (e.g. kernel
command-line or bootconfig) small internal storage, which would be
also encrypted with TPM's PRCs containing an array of LUKS2 header
and then look up that with SHA256 as the key.

Without knowing LUKS2 implementation to me these do not sound reaching
the impossible engineer problems so maybe this would be worth of
investigating...

BR, Jarkko