linux-kernel - Re: [RFC PATCH v2 0/4] tsm: Runtime measurement registers ABI

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Date: Wed, 14 Feb 2024 22:14:12 -0800
From: Dan Williams <dan.j.williams@...el.com>
To: "Xing, Cedric" <cedric.xing@...el.com>, James Bottomley
	<James.Bottomley@...senpartnership.com>, Dan Williams
	<dan.j.williams@...el.com>, Kuppuswamy Sathyanarayanan
	<sathyanarayanan.kuppuswamy@...ux.intel.com>, Dan Middleton
	<dan.middleton@...ux.intel.com>, Samuel Ortiz <sameo@...osinc.com>
CC: Qinkun Bao <qinkun@...gle.com>, "Yao, Jiewen" <jiewen.yao@...el.com>,
	Dionna Amalie Glaze <dionnaglaze@...gle.com>, <biao.lu@...el.com>,
	<linux-coco@...ts.linux.dev>, <linux-integrity@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2 0/4] tsm: Runtime measurement registers ABI

Xing, Cedric wrote:
> On 2/13/2024 8:05 AM, James Bottomley wrote:
[..]
> > The TCG crypto agile log format is
> > 
> >   index (32 bit),
> >   event tag (32 bit),
> >   digests array,
> >   sized event entry (up to 4GB)
> > 
> > So an IMA log entry can definitely be transformed into this format
> > (providing someone agrees to the tag or set of tags).  The slight
> > problem would be that none of the current IMA tools would understand
> > it, but that could be solved over time (the kernel could use the TCG
> > format internally but transform to the IMA format for the current
> > securityfs IMA log).
> > 
> Hi James,
> 
[..]
> Another problem of CEL is that NOT every byte of an event is 
> hashed/extended. CEL spec has defined for each "content_type" the subset 
> of bytes to hash, so a verifier must understand ALL content types to be 
> able to verify the integrity of a log. In other words, the integrity of 
> a "systemd" log can never be verified by a CEL conformant verifier.

Wait, James said, "crypto agile log format", not CEL. Crypto agile log
format looks more generic, no "recnum" for example.

[..]
> >> IMHO, we don't have to follow TCG2 format..
[..]
> > https://xkcd.com/927/
> > 
> That is funny :-D
> 
> I can't agree more, so "no log" I think is always an option.

So to me, "no log" means that instead of going from 14 standards going
to 15, the kernel is saying "whee, infinite userspace log formats!", an
abdication of its role to support a stable application ABI.

The job here to define a kernel de-facto standard for the tags that this
configs implementation of a cryto agile log emits, right? As James says:

"(providing someone agrees to the tag or set of tags)"