linux-kernel - Re: [PATCH v10 8/8] tpm: TPM 2.0 FIFO Interface

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Date:	Sun, 14 Dec 2014 15:40:05 -0500
From:	Stefan Berger <stefanb@...ux.vnet.ibm.com>
To:	Scot Doyle <lkml14@...tdoyle.com>
CC:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
	Peter Huewe <peterhuewe@....de>,
	Ashley Lai <ashley@...leylai.com>,
	Marcel Selhorst <tpmdd@...horst.net>,
	tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	josh@...htriplett.org, christophe.ricard@...il.com,
	jason.gunthorpe@...idianresearch.com,
	Will Arthur <will.c.arthur@...el.com>
Subject: Re: [PATCH v10 8/8] tpm: TPM 2.0 FIFO Interface

On 12/14/2014 01:27 PM, Scot Doyle wrote:
> On Sun, 14 Dec 2014, Stefan Berger wrote:
>> On 12/14/2014 10:40 AM, Jarkko Sakkinen wrote:
>>> On Sun, Dec 14, 2014 at 09:48:26AM -0500, Stefan Berger wrote:
>>>> On 12/12/2014 02:46 PM, Jarkko Sakkinen wrote:
>>>>> Detect TPM 2.0 by sending idempotent TPM 2.x command. Ordinals for
>>>>> TPM 2.0 are higher than TPM 1.x commands so this should be fail-safe.
>>>>> Using STS3 is unreliable because some chips just report 0xff and not
>>>>> what the spec says.
>>>> TPM TIS 1.2 can report either 0xff or 0x00 for sts3 since that part of
>>>> register was not defined for this version but only for a later version.
>>>> So,
>>>> unless the TIS 1.3 for TPM 2.0 is broken, it should report a bit _pattern_
>>>> (not plain 0x00 or 0xff) that you could apply the suggested mask to and
>>>> check then.
>>> I propose this: lets keep the bit ugly but approach for now and when
>>> there are TPM2 FIFOs available in the market move to your workaround.
>>> I think that would be the most reasonable middle road here.
>> You are now calling tpm2_gen_interrupt and are looking at the rc, which is the
>> rc from tpm_transmit_cmd, which seems to make sure that the sending of the
>> command went alright and the reception of the response. Is this good enough to
>> distinguish between a TPM 2 and a TPM 1.2? If you send a valid TPM 2 command
>> to a TPM 1.2 this will at least transmit the data ok, but the TPM will respond
>> with a TPM 1.2 tag in the response. The way I understand the code, the rc does
>> not include whether the response packet is a valid TPM 2 response packet and
>> lets you conclude to a TPM2. I do something similar in upcoming QEMU patches
>> where I send a valid TPM2 command for probing and if the tag(!) in the
>> response is a TPM2 tag (0x8001 = TPM_ST_NO_SESSIONS), then it's a TPM 2,
>> otherwise a TPM 1.2.
>>
>> Did you test this with a TPM 1.2 ?
>>
>>     Stefan
> One system's output, with a dev_info call to show the value of rc:
> [ 0.223837] tpm_tis 00:08: tpm2_gen_interrupt(chip, true) -> 0xa
> [ 0.223847] tpm_tis 00:08: 1.2 TPM (device-id 0xB, rev-id 16)
> [ 0.280468] tpm_tis 00:08: [Firmware Bug]: TPM interrupt not working, polling instead
>

Ok, good.

[We won't be able to use STS3 if the TIS of Jarkko's TPM2 is broken...]

     Stefan



    Stefan

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