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

[Brijesh Singh <brijesh.singh@amd.com>]

On 11/14/19 1:27 PM, Peter Gonda wrote:
> On Tue, Nov 12, 2019 at 2:27 PM Brijesh Singh <brijesh.singh@amd.com> wrote:
>>
>>
>> On 11/12/19 12:35 PM, Peter Gonda wrote:
>>> On Wed, Jul 10, 2019 at 1:13 PM Singh, Brijesh <brijesh.singh@amd.com> 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.