Index: uvm_user.c
===================================================================
RCS file: /cvsroot/src/sys/uvm/uvm_user.c,v
retrieving revision 1.14
diff -p -u -r1.14 uvm_user.c
--- uvm_user.c	2 Feb 2011 15:13:34 -0000	1.14
+++ uvm_user.c	12 Feb 2019 10:04:12 -0000
@@ -47,9 +47,17 @@ __KERNEL_RCSID(0, "$NetBSD: uvm_user.c,v
 void
 uvm_deallocate(struct vm_map *map, vaddr_t start, vsize_t size)
 {
+	vaddr_t end = round_page(start + size);
 
 	if (size == 0)
 		return;
 
-	uvm_unmap(map, trunc_page(start), round_page(start + size));
+	/*
+	 * If end ends up less than start, or both start and end are
+	 * zero, there was likely an overflow.  Saturate instead.
+	 */
+	if (end < start || (end == start && end == 0))
+		end = (vaddr_t)-1;
+
+	uvm_unmap(map, trunc_page(start), end);
 }