linux-kernel - Re: Linux DRTM on UEFI platforms

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Message-ID: <20220708045638.GA27939@srcf.ucam.org>
Date:   Fri, 8 Jul 2022 05:56:38 +0100
From:   Matthew Garrett <mjg59@...f.ucam.org>
To:     Brendan Trotter <btrotter@...il.com>
Cc:     "Daniel P. Smith" <dpsmith@...rtussolutions.com>,
        The development of GNU GRUB <grub-devel@....org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Daniel Kiper <daniel.kiper@...cle.com>,
        Alec Brown <alec.r.brown@...cle.com>,
        Kanth Ghatraju <kanth.ghatraju@...cle.com>,
        Ross Philipson <ross.philipson@...cle.com>,
        "piotr.krol@...eb.com" <piotr.krol@...eb.com>,
        "krystian.hebel@...eb.com" <krystian.hebel@...eb.com>,
        "persaur@...il.com" <persaur@...il.com>,
        "Yoder, Stuart" <stuart.yoder@....com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        "michal.zygowski@...eb.com" <michal.zygowski@...eb.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        "lukasz@...rylko.pl" <lukasz@...rylko.pl>,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        James Morris <jmorris@...ei.org>
Subject: Re: Linux DRTM on UEFI platforms

On Fri, Jul 08, 2022 at 01:06:19PM +0930, Brendan Trotter wrote:

> This leaves me wondering what your true motivation is. Are you trying
> to benefit GRUB/Trenchboot (at the expense of security, end-user
> convenience, distro installer hassle, etc); or trying to manufacture
> scope for future man-in-the middle attacks (by promoting a solution
> that requires something between firmware and kernel)?

The described mechanism doesn't require trusting the code that's in the 
middle - if the state is perturbed by this code, the measurements will 
be different, and the system will be untrusted. I agree that this 
implementation is more complicated than just leaving it all up to the 
kernel, but I'm having a *lot* of trouble seeing how this has any impact 
on its security. Jumping immediately to impugning the motivation of the 
people involved is entirely inappropriate.