Re: [Qemu-devel] [PATCH 5/5] tpm: tpm_passthrough: Fail startup if FE buffer size < BE buffer size

["Marc-André Lureau" <marcandre.lureau@redhat.com>]

Hi Stefan,

On Mon, Nov 06, 2017 at 07:58:56PM -0500, Stefan Berger wrote:
> If the requested buffer size of the frontend is smaller than the fixed
> buffer size of the host's TPM, fail the startup_tpm() interface function,
> which will make the device unusable. We fail it because the backend TPM
> could produce larger packets than what the frontend could pass to the OS.
> 
> The current combination of TIS frontend and either passthrough or emulator
> backend will not lead to this case since the TIS can support any size of
> buffer.
> 
> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
> ---
>  hw/tpm/tpm_passthrough.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/hw/tpm/tpm_passthrough.c b/hw/tpm/tpm_passthrough.c
> index ec755fe..66d5098 100644
> --- a/hw/tpm/tpm_passthrough.c
> +++ b/hw/tpm/tpm_passthrough.c
> @@ -304,6 +304,20 @@ static TPMBackend *tpm_passthrough_create(QemuOpts *opts)
>      return TPM_BACKEND(obj);
>  }
>  
> +static int tpm_passthrough_startup_tpm(TPMBackend *tb, uint32_t buffersize)
> +{
> +    TPMPassthruState *tpm_pt = TPM_PASSTHROUGH(tb);
> +
> +    if (buffersize && buffersize < tpm_pt->tpm_buffersize) {
> +        error_report("Requested buffer size of %u is smaller than host TPM's "
> +                     "fixed buffer size of %u",
> +                     buffersize, tpm_pt->tpm_buffersize);

Looks ok

> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
>  static TpmTypeOptions *tpm_passthrough_get_tpm_options(TPMBackend *tb)
>  {
>      TpmTypeOptions *options = g_new0(TpmTypeOptions, 1);
> @@ -362,6 +376,7 @@ static void tpm_passthrough_class_init(ObjectClass *klass, void *data)
>      tbc->opts = tpm_passthrough_cmdline_opts;
>      tbc->desc = "Passthrough TPM backend driver";
>      tbc->create = tpm_passthrough_create;
> +    tbc->startup_tpm = tpm_passthrough_startup_tpm;
>      tbc->reset = tpm_passthrough_reset;
>      tbc->cancel_cmd = tpm_passthrough_cancel_cmd;
>      tbc->get_tpm_established_flag = tpm_passthrough_get_tpm_established_flag;
> -- 
> 2.5.5

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>