Index: sys/amd64/vmm/amd/svm_support.S
===================================================================
--- sys/amd64/vmm/amd/svm_support.S
+++ sys/amd64/vmm/amd/svm_support.S
@@ -124,9 +124,21 @@
 	pop %rdx
 	mov %edx, %eax
 	shr $32, %rdx
-	mov $MSR_GSBASE, %ecx
+	mov $MSR_GSBASE, %rcx
 	wrmsr
 
+	/*
+	 * Clobber the remaining registers with guest contents so they
+	 * can't be misused.
+	 */
+	xor %rbp, %rbp
+	xor %rdi, %rdi
+	xor %rsi, %rsi
+	xor %r8, %r8
+	xor %r9, %r9
+	xor %r10, %r10
+	xor %r11, %r11
+
 	VLEAVE
 	ret
 END(svm_launch)
Index: sys/amd64/vmm/intel/vmx_support.S
===================================================================
--- sys/amd64/vmm/intel/vmx_support.S
+++ sys/amd64/vmm/intel/vmx_support.S
@@ -72,6 +72,20 @@
 	movq	VMXCTX_GUEST_RDI(%rdi),%rdi; /* restore rdi the last */
 
 /*
+ * Clobber the remaining registers with guest contents so they can't
+ * be misused.
+ */
+#define	VMX_GUEST_CLOBBER						\
+	xor	%rax, %rax;						\
+	xor	%rcx, %rcx;						\
+	xor	%rdx, %rdx;						\
+	xor	%rsi, %rsi;						\
+	xor	%r8, %r8;						\
+	xor	%r9, %r9;						\
+	xor	%r10, %r10;						\
+	xor	%r11, %r11;
+
+/*
  * Save and restore the host context.
  *
  * Assumes that %rdi holds a pointer to the 'vmxctx'.
@@ -232,6 +246,8 @@
 
 	VMX_HOST_RESTORE
 
+	VMX_GUEST_CLOBBER
+
 	/*
 	 * This will return to the caller of 'vmx_enter_guest()' with a return
 	 * value of VMX_GUEST_VMEXIT.