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

Andrew Cooper
2023-11-11T18:19:19Z

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