In a small bowl, mix oil, garlic, rosemary, salt and pepper. Place half of the marinade in each of two resealable plastic bags. Add pork to one bag and potatoes to the other bag. Seal bags and turn to coat; refrigerate 8 hours or overnight.
Preheat oven to 425°. Drain and discard marinades. Place meat and potatoes in a greased 2-qt. broiler-safe baking dish. Bake, uncovered, 20-25 minutes or until potatoes are almost tender. Broil 5 in. from heat for 4-5 minutes or until potatoes are tender and a thermometer inserted in pork reads 160°. Let stand 5 minutes before slicing.