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

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Message-ID: <22088ed3-51a4-415f-932c-db84c92a2812@intel.com>
Date: Wed, 7 Feb 2024 12:16:53 -0800
From: "Xing, Cedric" <cedric.xing@...el.com>
To: Dan Williams <dan.j.williams@...el.com>, James Bottomley
	<James.Bottomley@...senpartnership.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

On 2/6/2024 6:02 PM, Dan Williams wrote:
> James Bottomley wrote:
>> There isn't really anything more complex about an interface that takes
>> a log entry, and does the record an extend, than an interface which
>> takes a PCR extension value.  So best practice would say that you
>> should create the ABI that you can't get wrong (log and record) rather
>> than creating one that causes additional problems for userspace.
> 
> Agree, there's no need for the kernel to leave deliberately pointy edges
> for userspace to trip over.
> 
> Cedric, almost every time we, kernel community, build an interface where
> userspace says "trust us, we know what we are doing" it inevitably
> results later in "whoops, turns out it would have helped if the kernel
> enforced structure here". So the log ABI adds that structure for the
> primary use cases.

Dan, I agree with your statement generally. But with the precedent of 
TPM module not maintaining a log, I just wonder if the addition of log 
would cause problems or force more changes to existing usages than 
necessary. For example, IMA has its own log and if changed to use RTMR, 
how would those 2 logs interoperate? We would also need to decide on a 
log format that can accommodate all applications.