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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Matthew Garrett <mjg59@srcf.ucam.org>
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        Eric Biggers <ebiggers@kernel.org>,
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Subject: Re: [PATCH v6 06/14] x86: Add early SHA support for Secure Launch
 early measurements
In-Reply-To: <20230512161318.GA18400@srcf.ucam.org>
References: <20230504145023.835096-1-ross.philipson@oracle.com>
 <20230504145023.835096-7-ross.philipson@oracle.com>
 <20230510012144.GA1851@quark.localdomain>
 <20230512110455.GD14461@srcf.ucam.org>
 <CAMj1kXE8m5jCH3vW54ys=dE2-Vf_gnnueR6_g4Rq-LSJ5BqRjA@mail.gmail.com>
 <20230512112847.GF14461@srcf.ucam.org> <87pm75bs3v.ffs@tglx>
 <20230512161318.GA18400@srcf.ucam.org>
Date:   Fri, 12 May 2023 20:17:21 +0200
Message-ID: <873541bej2.ffs@tglx>
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On Fri, May 12 2023 at 17:13, Matthew Garrett wrote:
> On Fri, May 12, 2023 at 03:24:04PM +0200, Thomas Gleixner wrote:
>> On Fri, May 12 2023 at 12:28, Matthew Garrett wrote:
>> > Unless we assert that SHA-1 events are unsupported, it seems a bit odd 
>> > to force a policy on people who have both banks enabled. People with 
>> > mixed fleets are potentially going to be dealing with SHA-1 measurements 
>> > for a while yet, and while there's obviously a security benefit in using 
>> > SHA-2 instead it'd be irritating to have to maintain two attestation 
>> > policies.
>> 
>> Why?
>> 
>> If you have a mixed fleet then it's not too much asked to provide two
>> data sets. On a TPM2 system you can enforce SHA-2 and only fallback to
>> SHA-1 on TPM 1.2 hardware. No?
>
> No, beause having TPM2 hardware doesn't guarantee that your firmware 
> enables SHA-2 (which also means this is something that could change with 
> firmware updates, which means that refusing to support SHA-1 if the 
> SHA-2 banks are enabled could result in an entirely different policy 
> being required (and plausibly one that isn't implemented in their 
> existing tooling)

It's not rocket science to have both variants supported in tooling,
really.

What a mess.