linux-kernel - Re: [GIT PULL] New TPM driver and features

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Date:	Fri, 27 Jul 2012 08:08:28 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Kent Yoder <key@...ux.vnet.ibm.com>
CC:	James Morris <jmorris@...ei.org>,
	Peter Huewe <peter.huewe@...ineon.com>,
	Bryan Freed <bfreed@...omium.org>,
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [GIT PULL] New TPM driver and features

On 07/27/2012 07:29 AM, Kent Yoder wrote:
> Hi,
>
> On Thu, Jul 26, 2012 at 02:46:25PM -0700, H. Peter Anvin wrote:
>> On 07/26/2012 07:31 AM, Kent Yoder wrote:
>>>        hw_random: add support for the TPM chip as a hardware RNG source
>>
>> Could you clarify this?  rngd (the user of /dev/hw_random) already
>> has support for the TPM... is this fundamentally different (e.g. can
>> it coexist with tcsd being in use at the same time)?
>
>    These can coexist at the same time since /dev/tpm0 is only opened once
> from user-space (from tcsd) and this hwrng driver comes in through the
> kernel. There would be some amount of contention with the tpm, but its
> not likely to be noticable - grabbing rng data doesn't require any state
> in the tpm, like an auth session or key loading.
>
>    Since the rngd support for the tpm requires trousers, this patch will
> be useful in places where you don't want to have to deploy the full TSS,
> like embedded and early boot.
>

Actually the rngd support for the TPM *conflicts* with trousers... I was 
looking at adding trousers support when I stumbled over your patch. 
Your patch is better, because it solves the handover problem (rngd 
should normally be started as early as possible.)

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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