KVM: SEV: fix compat ABI for KVM_MEMORY_ENCRYPT_OP

The data structs for KVM_MEMORY_ENCRYPT_OP have different sizes for 32- and 64-bit
userspace, but they do not make any attempt to convert from one ABI to the other
when 32-bit userspace is running on 64-bit kernels.  This configuration never
worked, and SEV is only for 64-bit kernels so we're not breaking ABI on 32-bit
kernels.

Fix this by adding the appropriate padding; no functional change intended
for 64-bit userspace.
Reviewed-by: Michael Roth <michael.roth@amd.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/uapi/asm/kvm.h

@@ -694,6 +694,7 @@ enum sev_cmd_id {
 
 struct kvm_sev_cmd {
 	__u32 id;
+	__u32 pad0;
 	__u64 data;
 	__u32 error;
 	__u32 sev_fd;
@@ -704,28 +705,35 @@ struct kvm_sev_launch_start {
 	__u32 policy;
 	__u64 dh_uaddr;
 	__u32 dh_len;
+	__u32 pad0;
 	__u64 session_uaddr;
 	__u32 session_len;
+	__u32 pad1;
 };
 
 struct kvm_sev_launch_update_data {
 	__u64 uaddr;
 	__u32 len;
+	__u32 pad0;
 };
 
 
 struct kvm_sev_launch_secret {
 	__u64 hdr_uaddr;
 	__u32 hdr_len;
+	__u32 pad0;
 	__u64 guest_uaddr;
 	__u32 guest_len;
+	__u32 pad1;
 	__u64 trans_uaddr;
 	__u32 trans_len;
+	__u32 pad2;
 };
 
 struct kvm_sev_launch_measure {
 	__u64 uaddr;
 	__u32 len;
+	__u32 pad0;
 };
 
 struct kvm_sev_guest_status {
@@ -738,33 +746,43 @@ struct kvm_sev_dbg {
 	__u64 src_uaddr;
 	__u64 dst_uaddr;
 	__u32 len;
+	__u32 pad0;
 };
 
 struct kvm_sev_attestation_report {
 	__u8 mnonce[16];
 	__u64 uaddr;
 	__u32 len;
+	__u32 pad0;
 };
 
 struct kvm_sev_send_start {
 	__u32 policy;
+	__u32 pad0;
 	__u64 pdh_cert_uaddr;
 	__u32 pdh_cert_len;
+	__u32 pad1;
 	__u64 plat_certs_uaddr;
 	__u32 plat_certs_len;
+	__u32 pad2;
 	__u64 amd_certs_uaddr;
 	__u32 amd_certs_len;
+	__u32 pad3;
 	__u64 session_uaddr;
 	__u32 session_len;
+	__u32 pad4;
 };
 
 struct kvm_sev_send_update_data {
 	__u64 hdr_uaddr;
 	__u32 hdr_len;
+	__u32 pad0;
 	__u64 guest_uaddr;
 	__u32 guest_len;
+	__u32 pad1;
 	__u64 trans_uaddr;
 	__u32 trans_len;
+	__u32 pad2;
 };
 
 struct kvm_sev_receive_start {
@@ -772,17 +790,22 @@ struct kvm_sev_receive_start {
 	__u32 policy;
 	__u64 pdh_uaddr;
 	__u32 pdh_len;
+	__u32 pad0;
 	__u64 session_uaddr;
 	__u32 session_len;
+	__u32 pad1;
 };
 
 struct kvm_sev_receive_update_data {
 	__u64 hdr_uaddr;
 	__u32 hdr_len;
+	__u32 pad0;
 	__u64 guest_uaddr;
 	__u32 guest_len;
+	__u32 pad1;
 	__u64 trans_uaddr;
 	__u32 trans_len;
+	__u32 pad2;
 };
 
 #define KVM_X2APIC_API_USE_32BIT_IDS            (1ULL << 0)