KVM: x86: Copy filter arg outside kvm_vm_ioctl_set_msr_filter()

In the next patch we want to introduce a second caller to
set_msr_filter() which constructs its own filter list on the stack.
Refactor the original function so it takes it as argument instead of
reading it through copy_from_user().

Signed-off-by: Alexander Graf <graf@amazon.com>
Message-Id: <20221017184541.2658-3-graf@amazon.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Author: agraf

arch/x86/kvm/x86.c

@@ -6442,35 +6442,31 @@ static int kvm_add_msr_filter(struct kvm_x86_msr_filter *msr_filter,
 	return 0;
 }
 
-static int kvm_vm_ioctl_set_msr_filter(struct kvm *kvm, void __user *argp)
+static int kvm_vm_ioctl_set_msr_filter(struct kvm *kvm,
+				       struct kvm_msr_filter *filter)
 {
-	struct kvm_msr_filter __user *user_msr_filter = argp;
 	struct kvm_x86_msr_filter *new_filter, *old_filter;
-	struct kvm_msr_filter filter;
 	bool default_allow;
 	bool empty = true;
 	int r = 0;
 	u32 i;
 
-	if (copy_from_user(&filter, user_msr_filter, sizeof(filter)))
-		return -EFAULT;
-
-	if (filter.flags & ~KVM_MSR_FILTER_DEFAULT_DENY)
+	if (filter->flags & ~KVM_MSR_FILTER_DEFAULT_DENY)
 		return -EINVAL;
 
-	for (i = 0; i < ARRAY_SIZE(filter.ranges); i++)
-		empty &= !filter.ranges[i].nmsrs;
+	for (i = 0; i < ARRAY_SIZE(filter->ranges); i++)
+		empty &= !filter->ranges[i].nmsrs;
 
-	default_allow = !(filter.flags & KVM_MSR_FILTER_DEFAULT_DENY);
+	default_allow = !(filter->flags & KVM_MSR_FILTER_DEFAULT_DENY);
 	if (empty && !default_allow)
 		return -EINVAL;
 
 	new_filter = kvm_alloc_msr_filter(default_allow);
 	if (!new_filter)
 		return -ENOMEM;
 
-	for (i = 0; i < ARRAY_SIZE(filter.ranges); i++) {
-		r = kvm_add_msr_filter(new_filter, &filter.ranges[i]);
+	for (i = 0; i < ARRAY_SIZE(filter->ranges); i++) {
+		r = kvm_add_msr_filter(new_filter, &filter->ranges[i]);
 		if (r) {
 			kvm_free_msr_filter(new_filter);
 			return r;
@@ -6915,9 +6911,16 @@ long kvm_arch_vm_ioctl(struct file *filp,
 	case KVM_SET_PMU_EVENT_FILTER:
 		r = kvm_vm_ioctl_set_pmu_event_filter(kvm, argp);
 		break;
-	case KVM_X86_SET_MSR_FILTER:
-		r = kvm_vm_ioctl_set_msr_filter(kvm, argp);
+	case KVM_X86_SET_MSR_FILTER: {
+		struct kvm_msr_filter __user *user_msr_filter = argp;
+		struct kvm_msr_filter filter;
+
+		if (copy_from_user(&filter, user_msr_filter, sizeof(filter)))
+			return -EFAULT;
+
+		r = kvm_vm_ioctl_set_msr_filter(kvm, &filter);
 		break;
+	}
 	default:
 		r = -ENOTTY;
 	}