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

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Date:   Tue, 12 Nov 2019 16:27:25 -0600
From:   Brijesh Singh <brijesh.singh@....com>
To:     Peter Gonda <pgonda@...gle.com>
Cc:     brijesh.singh@....com, "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 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.


>
>> +
>> +       /* 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?


Same as above, I believe its required.


>
>> +
>> +       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?


Same as above, I believe its required. I will double check it.


>> +
>> +       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?


Yes, we could factor out this check into a separate function. Let me see
what I can do in next iteration. thanks for the feedbacks.

-Brijesh