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

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Date:   Tue, 12 Nov 2019 10:35:55 -0800
From:   Peter Gonda <pgonda@...gle.com>
To:     "Singh, Brijesh" <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 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?

> +
> +       /* copy the certificate blobs from userspace */
> +       pdh_cert = psp_copy_user_blob(params.pdh_cert_uaddr, params.pdh_cert_len);
> +       if (IS_ERR(pdh_cert)) {
> +               ret = PTR_ERR(pdh_cert);
> +               goto e_free;
> +       }
> +
> +       data->pdh_cert_address = __psp_pa(pdh_cert);
> +       data->pdh_cert_len = params.pdh_cert_len;
> +
> +       plat_cert = psp_copy_user_blob(params.plat_cert_uaddr, params.plat_cert_len);
> +       if (IS_ERR(plat_cert)) {
> +               ret = PTR_ERR(plat_cert);
> +               goto e_free_pdh;
> +       }

I think plat_cert is also only required if the guest policy SEV bit is
set. Can plat_cert also be optional?

> +
> +       data->plat_cert_address = __psp_pa(plat_cert);
> +       data->plat_cert_len = params.plat_cert_len;
> +
> +       amd_cert = psp_copy_user_blob(params.amd_cert_uaddr, params.amd_cert_len);
> +       if (IS_ERR(amd_cert)) {
> +               ret = PTR_ERR(amd_cert);
> +               goto e_free_plat_cert;
> +       }

I think amd_cert is also only required if the guest policy SEV bit is
set. Can amd_cert also be optional?

> +
> +       data->amd_cert_address = __psp_pa(amd_cert);
> +       data->amd_cert_len = params.amd_cert_len;
> +
> +       ret = -EINVAL;
> +       if (params.session_len > SEV_FW_BLOB_MAX_SIZE)
> +               goto e_free_amd_cert;
> +
> +       ret = -ENOMEM;
> +       session_data = kmalloc(params.session_len, GFP_KERNEL);
> +       if (!session_data)
> +               goto e_free_amd_cert;

This pattern of returning -EINVAL if a length is greater than
SEV_FW_BLOB_MAX_SIZE and -ENOMEM if kmalloc fails is used at
sev_launch_measure. And I think in your later patches you do similar,
did you consider factoring this out into a helper function similar to
psp_copy_user_blob?