Re: [PATCH v3 01/11] KVM: SVM: Add KVM_SEV SEND_START command

[Brijesh Singh]

On 11/14/19 1:27 PM, Peter Gonda wrote:
> On Tue, Nov 12, 2019 at 2:27 PM Brijesh Singh <brijesh.singh@xxxxxxx> wrote:
> > On 11/12/19 12:35 PM, Peter Gonda wrote:
> > > On Wed, Jul 10, 2019 at 1:13 PM Singh, Brijesh <brijesh.singh@xxxxxxx> wrote:
> > > > +static int sev_send_start(struct kvm *kvm, struct kvm_sev_cmd *argp)
> > > > +{
> > > > +       struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> > > > +       void *amd_cert = NULL, *session_data = NULL;
> > > > +       void *pdh_cert = NULL, *plat_cert = NULL;
> > > > +       struct sev_data_send_start *data = NULL;
> > > > +       struct kvm_sev_send_start params;
> > > > +       int ret;
> > > > +
> > > > +       if (!sev_guest(kvm))
> > > > +               return -ENOTTY;
> > > > +
> > > > +       if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data,
> > > > +                               sizeof(struct kvm_sev_send_start)))
> > > > +               return -EFAULT;
> > > > +
> > > > +       data = kzalloc(sizeof(*data), GFP_KERNEL);
> > > > +       if (!data)
> > > > +               return -ENOMEM;
> > > > +
> > > > +       /* userspace wants to query the session length */
> > > > +       if (!params.session_len)
> > > > +               goto cmd;
> > > > +
> > > > +       if (!params.pdh_cert_uaddr || !params.pdh_cert_len ||
> > > > +           !params.session_uaddr)
> > > > +               return -EINVAL;
> > > I think pdh_cert is only required if the guest policy SEV bit is set.
> > > Can pdh_cert be optional?
> >
> >
> > We don't cache the policy information in kernel, having said so we can
> > try caching it during the LAUNCH_START to optimize this case. I have to
> > check with FW folks but I believe all those fields are required. IIRC,
> > When I passed NULL then SEND_START failed for me. But I double check it
> > and update you on this.
>
>
> I must have misinterpreted the this line of the spec:
> "If GCTX.POLICY.SEV is 1, the PDH, PEK, CEK, ASK, and ARK certificates
> are validated."
> I thought that since they were not validated they were not needed.

I have confirmed that these fields are required by the SEND_START
even when GCTX.POLICY.SEV=0. The FW needs us to pass certificate
chain, if POLICY.SEV=1 then FW will validating the chain otherwise
ignore it.