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

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Message-Id: <D3H9ULV1NH4M.1A8EKXWZFTEF2@kernel.org>
Date: Fri, 16 Aug 2024 13:42:13 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Thomas Gleixner" <tglx@...utronix.de>, "Daniel P. Smith"
 <dpsmith@...rtussolutions.com>, "Eric W. Biederman"
 <ebiederm@...ssion.com>, "Eric Biggers" <ebiggers@...nel.org>
Cc: "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>, <mjg59@...f.ucam.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>, <andrew.cooper3@...rix.com>,
 <trenchboot-devel@...glegroups.com>
Subject: Re: [PATCH v9 06/19] x86: Add early SHA-1 support for Secure Launch
 early measurements

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@...nel.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