linux-kernel - Re: [PATCH RFC 3/3] tsm: Add TVM Measurement Sample Code

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Message-ID: <796ebe16-86a4-4109-9b80-91a238f975f0@intel.com>
Date: Sat, 14 Sep 2024 11:36:00 -0500
From: "Xing, Cedric" <cedric.xing@...el.com>
To: James Bottomley <James.Bottomley@...senPartnership.com>, Dan Williams
	<dan.j.williams@...el.com>, Samuel Ortiz <sameo@...osinc.com>, Lukas Wunner
	<lukas@...ner.de>, Dionna Amalie Glaze <dionnaglaze@...gle.com>, Qinkun Bao
	<qinkun@...gle.com>, Mikko Ylinen <mikko.ylinen@...ux.intel.com>, "Kuppuswamy
 Sathyanarayanan" <sathyanarayanan.kuppuswamy@...ux.intel.com>
CC: <linux-kernel@...r.kernel.org>, <linux-coco@...ts.linux.dev>
Subject: Re: [PATCH RFC 3/3] tsm: Add TVM Measurement Sample Code

On 9/12/2024 7:28 AM, James Bottomley wrote:
> On Sat, 2024-09-07 at 23:56 -0500, Cedric Xing wrote:
>> This sample kernel module demonstrates how to make MRs accessible to
>> user mode
>> through TSM.
>>
>> Once loaded, this module registers a virtual measurement provider
>> with the TSM
>> core and will result in the directory tree below.
>>
>> /sys/kernel/tsm/
>> └── measurement-example
>>      ├── config_mr
>>      ├── full_report
>>      ├── report_digest
>>      ├── rtmr0
>>      │   ├── append_event
>>      │   ├── digest
>>      │   ├── event_log
>>      │   └── hash_algo
>>      ├── rtmr1
>>      │   ├── append_event
>>      │   ├── digest
>>      │   ├── event_log
>>      │   └── hash_algo
>>      ├── static_mr
>>      └── user_data
> 
> I'm not sure this is the best structure to apply to logs with multiple
> banks (hash algorithms).  There needs to be a way to get the same
> registers measurement for each bank, but the log should sit above that
> (appending should extend all active banks)
> 
> How about
> 
> /sys/kernel/tsm/
> └──<measurement type>
>     ├──reg0
>     │   ├── <log format>
>     │   │   ├── append_event
>     │   │   └── event_log
>     │   ├── <hash algo>
>     │  ...  └── digest
>     ...
> 
> That way it supports multiple log formats (would be the job of the log
> extender to ensure compatibility) and multiple banks.
> 
I have considered this before. But I'm not sure how to (define/describe 
criteria to) match an MR with its log format. Also, MRs are arch 
dependent and may also vary from gen to gen. I'm afraid this might bring 
in more chaos than order.

-Cedric