Heat oven to 400° F with a rack in the middle position. Score the skin of the pork in a criss-cross diamond pattern every 1½ inches. Turn the pork skin-side down and rub with the garlic, rosemary, sage, 2 teaspoons salt, and ¾ teaspoon pepper. Roll up the pork with the skin on the outside and tie every 2 inches with kitchen twine. Place on a rimmed baking sheet.

Roast the pork for 1 hour. Reduce heat to 350° F and continue to roast until the skin is very crispy and pulls away from the meat easily, 2 to 2½ hours more. Transfer to a cutting board, tent loosely with foil, and let rest for 15 minutes before slicing.