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

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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.



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