Re: [PATCH v3 32/49] i386/sev: Don't return launch measurements for SEV-SNP guests

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Mar 20, 2024 at 03:39:28AM -0500, Michael Roth wrote:
> For SEV-SNP guests, launch measurement is queried from within the guest
> during attestation, so don't attempt to return it as part of
> query-sev-launch-measure.
> 
> Signed-off-by: Michael Roth <michael.roth@amd.com>
> ---
>  target/i386/sev.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/target/i386/sev.c b/target/i386/sev.c
> index b03d70a3d1..0c8e4bdb4c 100644
> --- a/target/i386/sev.c
> +++ b/target/i386/sev.c
> @@ -803,7 +803,9 @@ sev_launch_get_measure(Notifier *notifier, void *unused)
>  
>  static char *sev_get_launch_measurement(void)
>  {
> -    SevGuestState *sev_guest = SEV_GUEST(MACHINE(qdev_get_machine())->cgs);
> +    ConfidentialGuestSupport *cgs = MACHINE(qdev_get_machine())->cgs;
> +    SevGuestState *sev_guest =
> +        (SevGuestState *)object_dynamic_cast(OBJECT(cgs), TYPE_SEV_GUEST);
>  
>      if (sev_guest &&
>          SEV_COMMON(sev_guest)->state >= SEV_STATE_LAUNCH_SECRET) {

The QAPI docs for query-sev-launch-measurement should be updated
to reflect that this command is only valid to call for SEV/SEV-ES,
not SNP.

The error reoprting in qmp_query_sev_launch_measure leaves a little
to be desired just giving a generic message

   "SEV launch measurement is not available"

I think that this sev_get_launch_measurement method should report
a more fine grained error, to distinguish

  * Unavailable because we're not a SEV/SEV-ES guest
  * Unavailable because the guest hasn't reached launch state

With regards,
Daniel
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