Whisk balsamic vinegar, garlic, rosemary, honey, salt, and pepper together in a bowl. Place pork in a resealable plastic bag and pour balsamic mixture on top to coat. Squeeze out excess air, and seal the bag. Place the bag in a container to avoid leaks, and marinate in the refrigerator for 6 to 8 hours.

Preheat the oven to 425 degrees F (220 degrees C).

Remove pork from the marinade and shake off excess. Place pork in a roasting pan or baking dish. Reserve marinade.

Roast pork in the preheated oven until slightly pink in the center, about 25 minutes. An instant-read thermometer inserted into the center should read at least 145 degrees F (63 degrees C). Remove pork from the oven, place on a cutting board, and cover loosely with aluminum foil. Let rest for 10 to 20 minutes.

While pork is resting, pour marinade into a small saucepan and bring to a boil. Reduce heat to medium-low and simmer for 10 minutes. Serve with the roasted tenderloin.