linux-kernel - Re: [PATCH v9 06/19] x86: Add early SHA-1 support for Secure Launch early measurements

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Message-Id: <D3KUEGW4Q63K.NEFOY5C6ZG2O@kernel.org>
Date: Tue, 20 Aug 2024 18:26:31 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Matthew Garrett" <mjg59@...f.ucam.org>
Cc: "Andrew Cooper" <andrew.cooper3@...rix.com>, "Thomas Gleixner"
 <tglx@...utronix.de>, "Daniel P. Smith" <dpsmith@...rtussolutions.com>,
 "Eric W. Biederman" <ebiederm@...ssion.com>, "Eric Biggers"
 <ebiggers@...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>, <iommu@...ts.linux-foundation.org>,
 <mingo@...hat.com>, <bp@...en8.de>, <hpa@...or.com>,
 <dave.hansen@...ux.intel.com>, <ardb@...nel.org>,
 <James.Bottomley@...senpartnership.com>, <peterhuewe@....de>,
 <jgg@...pe.ca>, <luto@...capital.net>, <nivedita@...m.mit.edu>,
 <herbert@...dor.apana.org.au>, <davem@...emloft.net>, <corbet@....net>,
 <dwmw2@...radead.org>, <baolu.lu@...ux.intel.com>,
 <kanth.ghatraju@...cle.com>, <trenchboot-devel@...glegroups.com>
Subject: Re: [PATCH v9 06/19] x86: Add early SHA-1 support for Secure Launch
 early measurements

On Mon Aug 19, 2024 at 9:24 PM EEST, Matthew Garrett wrote:
> On Mon, Aug 19, 2024 at 09:05:47PM +0300, Jarkko Sakkinen wrote:
> > On Fri Aug 16, 2024 at 9:41 PM EEST, Matthew Garrett wrote:
> > > On Fri, Aug 16, 2024 at 02:22:04PM +0300, Jarkko Sakkinen wrote:
> > >
> > > > For (any) non-legacy features we can choose, which choices we choose to
> > > > support, and which we do not. This is not an oppositive view just saying
> > > > how it is, and platforms set of choices is not a selling argument.
> > >
> > > NIST still permits the use of SHA-1 until 2030, and the most significant 
> > > demonstrated weaknesses in it don't seem applicable to the use case 
> > > here. We certainly shouldn't encourage any new uses of it, and anyone 
> > > who's able to use SHA-2 should be doing that instead, but it feels like 
> > > people are arguing about not supporting hardware that exists in the real 
> > > world for vibes reasons rather than it being a realistically attackable 
> > > weakness (and if we really *are* that concerned about SHA-1, why are we 
> > > still supporting TPM 1.2 at all?)
> > 
> > We are life-supporting TPM 1.2 as long as necessary but neither the
> > support is extended nor new features will gain TPM 1.2 support. So
> > that is at least my policy for that feature.
>
> But the fact that we support it and provide no warning labels is a 
> pretty clear indication that we're not actively trying to prevent people 
> from using SHA-1 in the general case. Why is this a different case? 
> Failing to support it actually opens an entire separate set of footgun 
> opportunities in terms of the SHA-1 banks now being out of sync with the 
> SHA-2 ones, so either way we're leaving people open to making poor 
> choices.

This is a fair and enclosing argument. I get where you are coming from
now. Please as material for the commit message.

BR, Jarkko