KVM: SVM: nested: Don't allocate VMCB structures on stack

Do not allocate a vmcb_control_area and a vmcb_save_area on the stack,
as these structures will become larger with future extenstions of
SVM and thus the svm_set_nested_state() function will become a too large
stack frame.
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200907131613.12703-2-joro@8bytes.org

arch/x86/kvm/svm/nested.c

@@ -1060,10 +1060,14 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 	struct vmcb *hsave = svm->nested.hsave;
 	struct vmcb __user *user_vmcb = (struct vmcb __user *)
 		&user_kvm_nested_state->data.svm[0];
-	struct vmcb_control_area ctl;
-	struct vmcb_save_area save;
+	struct vmcb_control_area *ctl;
+	struct vmcb_save_area *save;
+	int ret;
 	u32 cr0;
 
+	BUILD_BUG_ON(sizeof(struct vmcb_control_area) + sizeof(struct vmcb_save_area) >
+		     KVM_STATE_NESTED_SVM_VMCB_SIZE);
+
 	if (kvm_state->format != KVM_STATE_NESTED_FORMAT_SVM)
 		return -EINVAL;
 
@@ -1095,13 +1099,22 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 		return -EINVAL;
 	if (kvm_state->size < sizeof(*kvm_state) + KVM_STATE_NESTED_SVM_VMCB_SIZE)
 		return -EINVAL;
-	if (copy_from_user(&ctl, &user_vmcb->control, sizeof(ctl)))
-		return -EFAULT;
-	if (copy_from_user(&save, &user_vmcb->save, sizeof(save)))
-		return -EFAULT;
 
-	if (!nested_vmcb_check_controls(&ctl))
-		return -EINVAL;
+	ret  = -ENOMEM;
+	ctl  = kzalloc(sizeof(*ctl),  GFP_KERNEL);
+	save = kzalloc(sizeof(*save), GFP_KERNEL);
+	if (!ctl || !save)
+		goto out_free;
+
+	ret = -EFAULT;
+	if (copy_from_user(ctl, &user_vmcb->control, sizeof(*ctl)))
+		goto out_free;
+	if (copy_from_user(save, &user_vmcb->save, sizeof(*save)))
+		goto out_free;
+
+	ret = -EINVAL;
+	if (!nested_vmcb_check_controls(ctl))
+		goto out_free;
 
 	/*
 	 * Processor state contains L2 state.  Check that it is
@@ -1109,15 +1122,15 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 	 */
 	cr0 = kvm_read_cr0(vcpu);
         if (((cr0 & X86_CR0_CD) == 0) && (cr0 & X86_CR0_NW))
-                return -EINVAL;
+		goto out_free;
 
 	/*
 	 * Validate host state saved from before VMRUN (see
 	 * nested_svm_check_permissions).
 	 * TODO: validate reserved bits for all saved state.
 	 */
-	if (!(save.cr0 & X86_CR0_PG))
-		return -EINVAL;
+	if (!(save->cr0 & X86_CR0_PG))
+		goto out_free;
 
 	/*
 	 * All checks done, we can enter guest mode.  L1 control fields
@@ -1126,15 +1139,21 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 	 * contains saved L1 state.
 	 */
 	copy_vmcb_control_area(&hsave->control, &svm->vmcb->control);
-	hsave->save = save;
+	hsave->save = *save;
 
 	svm->nested.vmcb = kvm_state->hdr.svm.vmcb_pa;
-	load_nested_vmcb_control(svm, &ctl);
+	load_nested_vmcb_control(svm, ctl);
 	nested_prepare_vmcb_control(svm);
 
 out_set_gif:
 	svm_set_gif(svm, !!(kvm_state->flags & KVM_STATE_NESTED_GIF_SET));
-	return 0;
+
+	ret = 0;
+out_free:
+	kfree(save);
+	kfree(ctl);
+
+	return ret;
 }
 
 struct kvm_x86_nested_ops svm_nested_ops = {