Grind garlic, salt, pepper, cumin, oregano, and coriander into a paste using a mortar and pestle.

Transfer 1/2 of the paste to a bowl. Add lime juice, orange juice, olive oil, and vinegar and whisk until smooth.

Cut several deep, 1-inch-long slits into the fatty side of the pork roast. Rub the remaining paste into the slits. Put roast into a 1-gallon resealable plastic bag. Pour citrus mixture into the bag to coat roast, then squeeze as much air from the bag as possible and seal. Refrigerate, turning occasionally, 8 hours to overnight.

Remove pork roast from refrigerator, transfer to a roasting pan, and let stand at room temperature for 30 minutes.

Preheat the oven to 400 degrees F (200 degrees C).