Re: [PATCH Part2 v6 28/49] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_FINISH command

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Replying inline to the patch (and not with a in-reply-to patch, as nitted by Sean Christopherson).

Am 21.06.22 um 01:08 schrieb Ashish Kalra:
From: Brijesh Singh <brijesh.singh@xxxxxxx>

The KVM_SEV_SNP_LAUNCH_FINISH finalize the cryptographic digest and stores
it as the measurement of the guest at launch.

While finalizing the launch flow, it also issues the LAUNCH_UPDATE command
to encrypt the VMSA pages.

If its an SNP guest, then VMSA was added in the RMP entry as
a guest owned page and also removed from the kernel direct map
so flush it later after it is transitioned back to hypervisor
state and restored in the direct map.

Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
---
  .../virt/kvm/x86/amd-memory-encryption.rst    |  22 ++++
  arch/x86/kvm/svm/sev.c                        | 119 ++++++++++++++++++
  include/uapi/linux/kvm.h                      |  14 +++
  3 files changed, 155 insertions(+)

diff --git a/Documentation/virt/kvm/x86/amd-memory-encryption.rst b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
index 62abd5c1f72b..750162cff87b 100644
--- a/Documentation/virt/kvm/x86/amd-memory-encryption.rst
+++ b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
@@ -514,6 +514,28 @@ Returns: 0 on success, -negative on error
  See the SEV-SNP spec for further details on how to build the VMPL permission
  mask and page type.
+21. KVM_SNP_LAUNCH_FINISH
+-------------------------
+
+After completion of the SNP guest launch flow, the KVM_SNP_LAUNCH_FINISH command can be
+issued to make the guest ready for the execution.
+
+Parameters (in): struct kvm_sev_snp_launch_finish
+
+Returns: 0 on success, -negative on error
+
+::
+
+        struct kvm_sev_snp_launch_finish {
+                __u64 id_block_uaddr;
+                __u64 id_auth_uaddr;
+                __u8 id_block_en;
+                __u8 auth_key_en;
+                __u8 host_data[32];
+        };
+
+
+See SEV-SNP specification for further details on launch finish input parameters.
References
  ==========
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index a9461d352eda..a5b90469683f 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2095,6 +2095,106 @@ static int snp_launch_update(struct kvm *kvm, struct kvm_sev_cmd *argp)
  	return ret;
  }
+static int snp_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp)
+{
+	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+	struct sev_data_snp_launch_update data = {};
+	int i, ret;
+
+	data.gctx_paddr = __psp_pa(sev->snp_context);
+	data.page_type = SNP_PAGE_TYPE_VMSA;
+
+	for (i = 0; i < kvm->created_vcpus; i++) {
+		struct vcpu_svm *svm = to_svm(xa_load(&kvm->vcpu_array, i));
+		u64 pfn = __pa(svm->sev_es.vmsa) >> PAGE_SHIFT;
+
+		/* Perform some pre-encryption checks against the VMSA */
+		ret = sev_es_sync_vmsa(svm);
+		if (ret)
+			return ret;
+
+		/* Transition the VMSA page to a firmware state. */
+		ret = rmp_make_private(pfn, -1, PG_LEVEL_4K, sev->asid, true);
+		if (ret)
+			return ret;
+
+		/* Issue the SNP command to encrypt the VMSA */
+		data.address = __sme_pa(svm->sev_es.vmsa);
+		ret = __sev_issue_cmd(argp->sev_fd, SEV_CMD_SNP_LAUNCH_UPDATE,
+				      &data, &argp->error);
+		if (ret) {
+			snp_page_reclaim(pfn);
+			return ret;
+		}
+
+		svm->vcpu.arch.guest_state_protected = true;
+	}
+
+	return 0;
+}
+
+static int snp_launch_finish(struct kvm *kvm, struct kvm_sev_cmd *argp)
+{
+	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+	struct sev_data_snp_launch_finish *data;
+	void *id_block = NULL, *id_auth = NULL;
+	struct kvm_sev_snp_launch_finish params;
+	int ret;
+
+	if (!sev_snp_guest(kvm))
+		return -ENOTTY;
+
+	if (!sev->snp_context)
+		return -EINVAL;
+
+	if (copy_from_user(&params, (void __user *)(uintptr_t)argp->data, sizeof(params)))
+		return -EFAULT;
+
+	/* Measure all vCPUs using LAUNCH_UPDATE before we finalize the launch flow. */
+	ret = snp_launch_update_vmsa(kvm, argp);

This poses a real problem for those, who want to precalculate the digest beforehand and sign their TEE without loading the TEE:
1. We don't know the contents of the VMSA, nor the hash of it.
2. Who guarantees, that future kernels have the same VMSA contents?

I would propose at least one additional ioctl parameter specifying the final VMSA for the SNP_PAGE_TYPE_VMSA snp_launch_update_vmsa.
This parameter could specify to use:
- the current VMSA
- or a VMSA resembling the CPU state on reset, where the contents is guaranteed to never change and have a defined digest
- or a user provided VMSA

+	if (ret)
+		return ret;
+
+	data = kzalloc(sizeof(*data), GFP_KERNEL_ACCOUNT);
+	if (!data)
+		return -ENOMEM;
+
+	if (params.id_block_en) {
+		id_block = psp_copy_user_blob(params.id_block_uaddr, KVM_SEV_SNP_ID_BLOCK_SIZE);
+		if (IS_ERR(id_block)) {
+			ret = PTR_ERR(id_block);
+			goto e_free;
+		}
+
+		data->id_block_en = 1;
+		data->id_block_paddr = __sme_pa(id_block);
+	}
+
+	if (params.auth_key_en) {

The `params.auth_key_en` indicator does _not_ specify, whether an ID_AUTH struct should be sent or not,
but wheter the ID_AUTH struct contains an author key or not. The firmware always expects an ID_AUTH block.

So, please move the upper `if` to enclose only `data->auth_key_en = 1;`, or use my patch sent in-reply to this mail yesterday.

+		id_auth = psp_copy_user_blob(params.id_auth_uaddr, KVM_SEV_SNP_ID_AUTH_SIZE);
+		if (IS_ERR(id_auth)) {
+			ret = PTR_ERR(id_auth);
+			goto e_free_id_block;
+		}
+
+		data->auth_key_en = 1;
+		data->id_auth_paddr = __sme_pa(id_auth);
+	}
+
+	data->gctx_paddr = __psp_pa(sev->snp_context);
+	ret = sev_issue_cmd(kvm, SEV_CMD_SNP_LAUNCH_FINISH, data, &argp->error);
+
+	kfree(id_auth);
+
+e_free_id_block:
+	kfree(id_block);
+
+e_free:
+	kfree(data);
+
+	return ret;
+}
+
  int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
  {
  	struct kvm_sev_cmd sev_cmd;
@@ -2191,6 +2291,9 @@ int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
  	case KVM_SEV_SNP_LAUNCH_UPDATE:
  		r = snp_launch_update(kvm, &sev_cmd);
  		break;
+	case KVM_SEV_SNP_LAUNCH_FINISH:
+		r = snp_launch_finish(kvm, &sev_cmd);
+		break;
  	default:
  		r = -EINVAL;
  		goto out;
@@ -2696,11 +2799,27 @@ void sev_free_vcpu(struct kvm_vcpu *vcpu)
svm = to_svm(vcpu); + /*
+	 * If its an SNP guest, then VMSA was added in the RMP entry as
+	 * a guest owned page. Transition the page to hypervisor state
+	 * before releasing it back to the system.
+	 * Also the page is removed from the kernel direct map, so flush it
+	 * later after it is transitioned back to hypervisor state and
+	 * restored in the direct map.
+	 */
+	if (sev_snp_guest(vcpu->kvm)) {
+		u64 pfn = __pa(svm->sev_es.vmsa) >> PAGE_SHIFT;
+
+		if (host_rmp_make_shared(pfn, PG_LEVEL_4K, false))
+			goto skip_vmsa_free;
+	}
+
  	if (vcpu->arch.guest_state_protected)
  		sev_flush_encrypted_page(vcpu, svm->sev_es.vmsa);
__free_page(virt_to_page(svm->sev_es.vmsa)); +skip_vmsa_free:
  	if (svm->sev_es.ghcb_sa_free)
  		kvfree(svm->sev_es.ghcb_sa);
  }
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 9b36b07414ea..5a4662716b6a 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1814,6 +1814,7 @@ enum sev_cmd_id {
  	KVM_SEV_SNP_INIT,
  	KVM_SEV_SNP_LAUNCH_START,
  	KVM_SEV_SNP_LAUNCH_UPDATE,
+	KVM_SEV_SNP_LAUNCH_FINISH,
KVM_SEV_NR_MAX,
  };
@@ -1948,6 +1949,19 @@ struct kvm_sev_snp_launch_update {
  	__u8 vmpl1_perms;
  };
+#define KVM_SEV_SNP_ID_BLOCK_SIZE 96
+#define KVM_SEV_SNP_ID_AUTH_SIZE	4096
+#define KVM_SEV_SNP_FINISH_DATA_SIZE	32
+
+struct kvm_sev_snp_launch_finish {
+	__u64 id_block_uaddr;
+	__u64 id_auth_uaddr;
+	__u8 id_block_en;
+	__u8 auth_key_en;
+	__u8 host_data[KVM_SEV_SNP_FINISH_DATA_SIZE];
+	__u8 pad[6];
+};
+
  #define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1 << 0)
  #define KVM_DEV_ASSIGN_PCI_2_3		(1 << 1)
  #define KVM_DEV_ASSIGN_MASK_INTX	(1 << 2)




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