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.
Meanwhile, preheat the oven to 400 degrees F (200 degrees C).
Roast pork in the preheated oven for 30 minutes. Reduce the heat to 375 degrees F (190 degrees C) and continue cooking until no longer pink in the center, about 2 hours more. An instant-read thermometer inserted into the center should read at least 170 degrees F (75 degrees C).