linux-kernel - Re: [PATCH v8 06/15] x86: Add early SHA support for Secure Launch early measurements

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Message-ID: <e641e2f1-16cf-4717-8a1f-8afac2644efe@citrix.com>
Date: Fri, 23 Feb 2024 18:20:27 +0000
From: Andrew Cooper <andrew.cooper3@...rix.com>
To: Eric Biggers <ebiggers@...nel.org>,
 Andrew Cooper <andrew.cooper3@...rix.com>
Cc: Ard Biesheuvel <ardb@...nel.org>,
 Ross Philipson <ross.philipson@...cle.com>, linux-kernel@...r.kernel.org,
 x86@...nel.org, linux-integrity@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-crypto@...r.kernel.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, dave.hansen@...ux.intel.com,
 mjg59@...f.ucam.org, James.Bottomley@...senpartnership.com,
 peterhuewe@....de, jarkko@...nel.org, jgg@...pe.ca, luto@...capital.net,
 nivedita@...m.mit.edu, herbert@...dor.apana.org.au, davem@...emloft.net,
 kanth.ghatraju@...cle.com, trenchboot-devel@...glegroups.com
Subject: Re: [PATCH v8 06/15] x86: Add early SHA support for Secure Launch
 early measurements

On 23/02/2024 5:54 pm, Eric Biggers wrote:
> On Fri, Feb 23, 2024 at 04:42:11PM +0000, Andrew Cooper wrote:
>> Yes, and I agree.  We're not looking to try and force this in with
>> underhand tactics.
>>
>> But a blind "nack to any SHA-1" is similarly damaging in the opposite
>> direction.
>>
> Well, reviewers have said they'd prefer that SHA-1 not be included and given
> some thoughtful reasons for that.  But also they've given suggestions on how to
> make the SHA-1 support more palatable, such as splitting it into a separate
> patch and giving it a proper justification.
>
> All suggestions have been ignored.

The public record demonstrates otherwise.

But are you saying that you'd be happy if the commit message read
something more like:

---8<---
For better or worse, Secure Launch needs SHA-1 and SHA-256.

The choice of hashes used lie with the platform firmware, not with
software, and is often outside of the users control.

Even if we'd prefer to use SHA-256-only, if firmware elected to start us
with the SHA-1 and SHA-256 backs active, we still need SHA-1 to parse
the TPM event log thus far, and deliberately cap the SHA-1 PCRs in order
to safely use SHA-256 for everything else.
---

?

~Andrew