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

[Jarkko Sakkinen]

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