linux-kernel - Re: [PATCH v8 08/10] tpm: Proxy driver for supporting multiple emulated TPMs

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Date:	Wed, 16 Mar 2016 09:49:57 -0400
From:	Stefan Berger <stefanb@...ux.vnet.ibm.com>
To:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:	tpmdd-devel@...ts.sourceforge.net, jgunthorpe@...idianresearch.com,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-api@...r.kernel.org, dhowells@...hat.com
Subject: Re: [PATCH v8 08/10] tpm: Proxy driver for supporting multiple
 emulated TPMs

On 03/16/2016 08:09 AM, Jarkko Sakkinen wrote:
> On Sun, Mar 13, 2016 at 06:54:38PM -0400, Stefan Berger wrote:
>> This patch implements a proxy driver for supporting multiple emulated TPMs
>> in a system.
>>
>> The driver implements a device /dev/vtpmx that is used to created
>> a client device pair /dev/tpmX (e.g., /dev/tpm10) and a server side that
>> is accessed using a file descriptor returned by an ioctl.
>> The device /dev/tpmX is the usual TPM device created by the core TPM
>> driver. Applications or kernel subsystems can send TPM commands to it
>> and the corresponding server-side file descriptor receives these
>> commands and delivers them to an emulated TPM.
>>
>> Signed-off-by: Stefan Berger <stefanb@...ux.vnet.ibm.com>
>> CC: linux-kernel@...r.kernel.org
>> CC: linux-doc@...r.kernel.org
>> CC: linux-api@...r.kernel.org
> Alternative to this would be to have /dev/vtpmx create:
>
> * /dev/vtpm0 for the server
> * /dev/tpm0 for the client
>
> This is how David Howell's PoC worked and that's why I want
> to make this alternative visible.

My initial implementation had this as well.

>
> The server could even respawn without container noticing it.
> This solution have better availability properties.

A TPM should be stable enough to not have to be respawned...

     Stefan