linux-kernel - [PATCH v6 2/2] KVM: SEV: Add KVM_SEV_SNP_ENABLE_REQ

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Message-ID: <20250428195113.392303-3-michael.roth@amd.com>
Date: Mon, 28 Apr 2025 14:51:13 -0500
From: Michael Roth <michael.roth@....com>
To: <kvm@...r.kernel.org>
CC: <linux-coco@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
	<pbonzini@...hat.com>, <seanjc@...gle.com>, <jroedel@...e.de>,
	<thomas.lendacky@....com>, <liam.merwick@...cle.com>,
	<dionnaglaze@...gle.com>, <huibo.wang@....com>
Subject: [PATCH v6 2/2] KVM: SEV: Add KVM_SEV_SNP_ENABLE_REQ_CERTS command

Introduce a new command for KVM_MEMORY_ENCRYPT_OP ioctl that can be used
to enable fetching of endorsement key certificates from userspace via
the new KVM_EXIT_SNP_REQ_CERTS exit type. Also introduce a new
KVM_X86_SEV_SNP_REQ_CERTS KVM device attribute so that userspace can
query whether the kernel supports the new command/exit.

Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Michael Roth <michael.roth@....com>
---
 .../virt/kvm/x86/amd-memory-encryption.rst      | 17 ++++++++++++++++-
 arch/x86/include/uapi/asm/kvm.h                 |  2 ++
 arch/x86/kvm/svm/sev.c                          | 17 ++++++++++++++++-
 3 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/Documentation/virt/kvm/x86/amd-memory-encryption.rst b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
index 1ddb6a86ce7f..cd680f129431 100644
--- a/Documentation/virt/kvm/x86/amd-memory-encryption.rst
+++ b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
@@ -572,6 +572,17 @@ Returns: 0 on success, -negative on error
 See SNP_LAUNCH_FINISH in the SEV-SNP specification [snp-fw-abi]_ for further
 details on the input parameters in ``struct kvm_sev_snp_launch_finish``.
 
+21. KVM_SEV_SNP_ENABLE_REQ_CERTS
+--------------------------------
+
+The KVM_SEV_SNP_ENABLE_REQ_CERTS command will configure KVM to exit to
+userspace with a ``KVM_EXIT_SNP_REQ_CERTS`` exit type as part of handling
+a guest attestation report, which will to allow userspace to provide a
+certificate corresponding to the endorsement key used by firmware to sign
+that attestation report.
+
+Returns: 0 on success, -negative on error
+
 Device attribute API
 ====================
 
@@ -579,11 +590,15 @@ Attributes of the SEV implementation can be retrieved through the
 ``KVM_HAS_DEVICE_ATTR`` and ``KVM_GET_DEVICE_ATTR`` ioctls on the ``/dev/kvm``
 device node, using group ``KVM_X86_GRP_SEV``.
 
-Currently only one attribute is implemented:
+The following attributes are currently implemented:
 
 * ``KVM_X86_SEV_VMSA_FEATURES``: return the set of all bits that
   are accepted in the ``vmsa_features`` of ``KVM_SEV_INIT2``.
 
+* ``KVM_X86_SEV_SNP_REQ_CERTS``: return a value of 1 if the kernel supports the
+  ``KVM_EXIT_SNP_REQ_CERTS`` exit, which allows for fetching endorsement key
+  certificates from userspace for each SNP attestation request the guest issues.
+
 Firmware Management
 ===================
 
diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
index 225a12e0d5d6..24045279dbea 100644
--- a/arch/x86/include/uapi/asm/kvm.h
+++ b/arch/x86/include/uapi/asm/kvm.h
@@ -468,6 +468,7 @@ struct kvm_sync_regs {
 /* vendor-specific groups and attributes for system fd */
 #define KVM_X86_GRP_SEV			1
 #  define KVM_X86_SEV_VMSA_FEATURES	0
+#  define KVM_X86_SEV_SNP_REQ_CERTS	1
 
 struct kvm_vmx_nested_state_data {
 	__u8 vmcs12[KVM_STATE_NESTED_VMX_VMCS_SIZE];
@@ -708,6 +709,7 @@ enum sev_cmd_id {
 	KVM_SEV_SNP_LAUNCH_START = 100,
 	KVM_SEV_SNP_LAUNCH_UPDATE,
 	KVM_SEV_SNP_LAUNCH_FINISH,
+	KVM_SEV_SNP_ENABLE_REQ_CERTS,
 
 	KVM_SEV_NR_MAX,
 };
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index b74e2be2cbaf..d5b4f308ab3a 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2123,7 +2123,9 @@ int sev_dev_get_attr(u32 group, u64 attr, u64 *val)
 	case KVM_X86_SEV_VMSA_FEATURES:
 		*val = sev_supported_vmsa_features;
 		return 0;
-
+	case KVM_X86_SEV_SNP_REQ_CERTS:
+		*val = sev_snp_enabled ? 1 : 0;
+		return 0;
 	default:
 		return -ENXIO;
 	}
@@ -2535,6 +2537,16 @@ static int snp_launch_finish(struct kvm *kvm, struct kvm_sev_cmd *argp)
 	return ret;
 }
 
+static int snp_enable_certs(struct kvm *kvm)
+{
+	if (kvm->created_vcpus || !sev_snp_guest(kvm))
+		return -EINVAL;
+
+	to_kvm_sev_info(kvm)->snp_certs_enabled = true;
+
+	return 0;
+}
+
 int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
 {
 	struct kvm_sev_cmd sev_cmd;
@@ -2640,6 +2652,9 @@ int sev_mem_enc_ioctl(struct kvm *kvm, void __user *argp)
 	case KVM_SEV_SNP_LAUNCH_FINISH:
 		r = snp_launch_finish(kvm, &sev_cmd);
 		break;
+	case KVM_SEV_SNP_ENABLE_REQ_CERTS:
+		r = snp_enable_certs(kvm);
+		break;
 	default:
 		r = -EINVAL;
 		goto out;
-- 
2.25.1