Re: [PATCH] tpm: fixed be_buffer_size size in in tpm_crb

[Stefan Berger]

On 12/26/21 21:24, Stefan Berger wrote:
> On 12/25/21 07:38, Yuri Konotopov wrote:
> > Trying to boot VM with TPM 2.0 CRB in passthrough mode without this 
> > change
> > I got "Requested buffer size of 3968 is smaller than host TPM's fixed
> > buffer size of 4096".
>
> I suppose the host has a TIS interface.
>
> The reason it gives this message is that the response this TPM may 
> send back could be 4096 bytes in size but the CRB of the VM can only 
> catch 3968 bytes, so there's a mismatch. You may not be able to use 
> the CRB in passthrough mode. I would try to have the VM use the TIS.


For TPM passthrough the host TPM's buffer size basically has to match 
the VM's buffer size so that

- apps inside the VM cannot create longer commands than what the host 
device can accept

- apps inside the VM cannot create commands that cause the TPM to return 
responses that are bigger than what the VM's TPM buffer can accept

  Stefan