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

Jarkko Sakkinen
2024-08-16T10:42:23Z

On Thu Aug 15, 2024 at 10:10 PM EEST, Thomas Gleixner wrote:
> On Thu, Aug 15 2024 at 13:38, Daniel P. Smith wrote:
> > On 5/31/24 09:54, Eric W. Biederman wrote:
> >> Eric Biggers <ebiggers@kernel.org> writes:
> >>> That paragraph is also phrased as a hypothetical, "Even if we'd prefer to use
> >>> SHA-256-only". That implies that you do not, in fact, prefer SHA-256 only. Is
> >>> that the case? Sure, maybe there are situations where you *have* to use SHA-1,
> >>> but why would you not at least *prefer* SHA-256?
> >>
> >> Yes. Please prefer to use SHA-256.
> >>
> >> Have you considered implementing I think it is SHA1-DC (as git has) that
> >> is compatible with SHA1 but blocks the known class of attacks where
> >> sha1 is actively broken at this point?
> >
> > We are using the kernel's implementation, addressing what the kernel
> > provides is beyond our efforts. Perhaps someone who is interested in
> > improving the kernel's SHA1 could submit a patch implementing/replacing
> > it with SHA1-DC, as I am sure the maintainers would welcome the help.

Git also has a bit more wide than secure launch, and the timeline is
also completely different. Git maintains legacy, while has also
introduced SHA-256 support in 2018. This as a new feature in the kernel
stack.

The purpose of SHA1-DC has obviously been to extend the lifespan, not
fix SHA-1.

Linux will be better of not adding anything new related to SHA-1 or
TPM 1.2. They still have a maintenance cost and I think that time
would be better spent of for almost anything else (starting from
taking your trashes out or boiling coffee) ;-)

>
> Well, someone who is interested to get his "secure" code merged should
> have a vested interested to have a non-broken SHA1 implementation if
> there is a sensible requirement to use SHA1 in that new "secure" code,
> no?
>
> Just for the record. The related maintainers can rightfully decide to
> reject known broken "secure" code on a purely technical argument.
>
> Thanks,
>
> tglx

BR, Jarkko