linux-kernel - Re: [PATCH v7 06/13] x86: Add early SHA support for Secure Launch early measurements

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Date:   Sat, 11 Nov 2023 18:19:12 +0000
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     Eric Biggers <ebiggers@...nel.org>,
        Ross Philipson <ross.philipson@...cle.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-integrity@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-crypto@...r.kernel.org, iommu@...ts.linux-foundation.org,
        kexec@...ts.infradead.org, linux-efi@...r.kernel.org,
        dpsmith@...rtussolutions.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, hpa@...or.com, ardb@...nel.org, mjg59@...f.ucam.org,
        James.Bottomley@...senpartnership.com, luto@...capital.net,
        nivedita@...m.mit.edu, kanth.ghatraju@...cle.com,
        trenchboot-devel@...glegroups.com
Subject: Re: [PATCH v7 06/13] x86: Add early SHA support for Secure Launch
 early measurements

On 11/11/2023 5:44 pm, Eric Biggers wrote:
> On Fri, Nov 10, 2023 at 05:27:44PM -0500, Ross Philipson wrote:
>>  arch/x86/boot/compressed/early_sha1.c   | 12 ++++
>>  lib/crypto/sha1.c                       | 81 +++++++++++++++++++++++++
> It's surprising to still see this new use of SHA-1 after so many people objected
> to it in the v6 patchset.  It's also frustrating that the SHA-1 support is still
> being obfuscated by being combined in one patch with SHA-2 support, perhaps in
> an attempt to conflate the two algorithms and avoid having to give a rationale
> for the inclusion of SHA-1.  Finally, new functions should not be added to
> lib/crypto/sha1.c unless those functions have multiple users.

The rational was given.  Let me reiterate it.

There are real TPMs in the world that can't use SHA-2.  The use of SHA-1
is necessary to support DRTM on such systems, and there are real users
of such configurations.

DRTM with SHA-1-only is a damnsight better than no DTRM, even if SHA-1
is getting a little long in the tooth.

So unless you have a credible plan to upgrade every non-SHA-2 TPM in the
world, you are deliberately breaking part of the usecase paying for the
effort of trying to upstream DRTM support into Linux.

~Andrew