Mailing List Archive

xen-devel-bounces@lists.xensource.com wrote on 11/05/2006 11:44:14 AM:

> The TPM protocol in contrast assumes a
> > reliable connection from the computer to the device and that all
> commands
> > finish correctly and responses are received by the apps *and* that
> requests
> > are not resent. How does the block driver handle this? Will the
> frontend
> > driver still receive explicit notification of a shutdown?
>
> Blkfront remembers un-acknowledged requests and reissues them after a
> re-connect. It doesn't matter whether the requests have previously been

I cannot possibly reissue commands like a TPM_Extend(value). It's
performing a hashing operation on a register of the TPM using a formular
like

PCR_n = SHA1(PCR_n || value)

where || is a concatenation of two byte arrays.

So issuing this command twice would put the TPM's PCR register into a
state that it is not supposed to be in.

> issued or not, as we know there will be no reordering hazards within the
> request stream, as there are no ordering guarantees. It currently
> doesn't use the suspend notification.

Unfortunately the TPM is a device with different constraints.

Stefan

PS: Specs for the TPM are here:
https://www.trustedcomputinggroup.org/specs/TPM/tpmwg-mainrev62_Part3_Commands.pdf
page 114 talks about the TPM_Extend command.


>
> Ian
>
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