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

[Stefan Berger]

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.

   Stefan


> Looks like it can not be less than backend buffer size nor less than
> CRB_CTRL_CMD_SIZE.
>
> Signed-off-by: Yuri Konotopov <ykonotopov@gnome.org>
> ---
>   hw/tpm/tpm_crb.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/tpm/tpm_crb.c b/hw/tpm/tpm_crb.c
> index 58ebd1469c..8243645453 100644
> --- a/hw/tpm/tpm_crb.c
> +++ b/hw/tpm/tpm_crb.c
> @@ -270,7 +270,7 @@ static void tpm_crb_reset(void *dev)
>       s->regs[R_CRB_CTRL_RSP_SIZE] = CRB_CTRL_CMD_SIZE;
>       s->regs[R_CRB_CTRL_RSP_ADDR] = TPM_CRB_ADDR_BASE + A_CRB_DATA_BUFFER;
>   
> -    s->be_buffer_size = MIN(tpm_backend_get_buffer_size(s->tpmbe),
> +    s->be_buffer_size = MAX(tpm_backend_get_buffer_size(s->tpmbe),
>                               CRB_CTRL_CMD_SIZE);
>   
>       if (tpm_backend_startup_tpm(s->tpmbe, s->be_buffer_size) < 0) {