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

[Stefan Berger]

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

> >      Stefan
> /Jarkko

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