linux-kernel - Re: [PATCH v2 3/3] tpm: vtpm_proxy: Add ioctl to request locality prepended to command

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Message-Id: <2c20fc62-938a-a6da-dbb2-70711b84996d@linux.vnet.ibm.com>
Date:   Wed, 10 May 2017 09:20:14 -0400
From:   Stefan Berger <stefanb@...ux.vnet.ibm.com>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     tpmdd-devel@...ts.sourceforge.net,
        LSM List <linux-security-module@...r.kernel.org>,
        jgunthorpe@...idianresearch.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] tpm: vtpm_proxy: Add ioctl to request locality
 prepended to command

On 05/10/2017 08:47 AM, Jarkko Sakkinen wrote:
> On Tue, May 09, 2017 at 11:49:05AM -0400, Stefan Berger wrote:
>> On 05/08/2017 07:43 PM, Jarkko Sakkinen wrote:
>>> On Thu, May 04, 2017 at 04:03:18PM -0400, Stefan Berger wrote:
>>>> On 05/04/2017 02:40 PM, Jarkko Sakkinen wrote:
>>>>> On Thu, May 04, 2017 at 07:14:27AM -0400, Stefan Berger wrote:
>>>>>> On 05/04/2017 05:17 AM, Jarkko Sakkinen wrote:
>>>>>>> On Wed, May 03, 2017 at 07:40:48PM -0400, Stefan Berger wrote:
>>>>>>>> On 05/03/2017 06:37 PM, Jarkko Sakkinen wrote:
>>>>>>>>> On Fri, Apr 28, 2017 at 09:02:18AM -0400, Stefan Berger wrote:
>>>>>>>>>> Add an ioctl to request that the locality be prepended to every TPM
>>>>>>>>>> command.
>>>>>>>>> Don't really understand this change. Why locality is prenpended?
>>>>>>>> Commands can be executed under locality 0-3 and for some commands it is
>>>>>>>> important to know which locality a user may have chosen. How else should we
>>>>>>>> convey that locality to the TPM emulator ?
>>>>>>> Why this is not in the commit message?
>>>>>>>
>>>>>>> More scalable way to do this would be to have a set of vtpm proxy
>>>>>>> commands. There could be a command for requesting and releasing
>>>>>>> locality. That would be more clean.
>>>>>> I would think that if someone wanted to use locality it's the client using
>>>>>> /dev/tpm(rm)0 calling an ioctl or so and the vtpm proxy then merely passing
>>>>>> that locality to the backend (TPM emulator). I suppose the intention is to
>>>>>> support something like that following the addition of the new functions
>>>>>> request_locality and release_locality?
>>>>> What if we later on want to pass something else than locality to the
>>>>> backend? How that will work out?
>>>> 'push' more data in front. 'pop' off by recipient. We could wrap the command
>>>> in some form.
>>>>
>>>>       Stefan
>>> I would find having a set of special commands cleaner. Prepending sounds
>>> like a quick hack to me, not really something that should exist in the
>>> mainline.
>> Along the lines of this here?
>>
>> uint32_2 command
>> uint32_2 totlength
>> uint8_t locality
>> uint8_t buffer[]  <- the actual TPM command
>>
>>
>> With a command code like VTPM_PROXY_CMD_TPM_CMD = 1.
>>
>>     Stefan
> That would break binary compability.

That's why I am adding that additional flag that allows a client to 
choose whether it wants the TPM command wrapped (or locality prepended) 
so that it knows what to expect from the driver. I don't think that 
breaks compatibility.

>
> I would suggest allocating CC's backwards starting from 0xFFFFFFFF for
> these control messages and send them in regular TPM command layout. A
> bit similar idea as we have in the RM.
>
> /Jarkko
>