linux-kernel - Re: [PATCH v3 01/11] KVM: SVM: Add KVM_SEV SEND

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Date:   Thu, 14 Nov 2019 11:27:38 -0800
From:   Peter Gonda <pgonda@...gle.com>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Joerg Roedel <joro@...tes.org>, Borislav Petkov <bp@...e.de>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 01/11] KVM: SVM: Add KVM_SEV SEND_START command

On Tue, Nov 12, 2019 at 2:27 PM Brijesh Singh <brijesh.singh@....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@....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.