Re: [PATCH v6 2/2] KVM: SEV: Add KVM_SEV_SNP_ENABLE_REQ_CERTS command

[Liam Merwick <liam.merwick@oracle.com>]

On 28/04/2025 20:51, Michael Roth wrote:
> 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@google.com>
> Signed-off-by: Michael Roth <michael.roth@amd.com>

Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Tested-by: Liam Merwick <liam.merwick@oracle.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;