I mean, "rock music" is a very broad term, or course. Once upon a time, "rock" was Elvis Presley. Now we have Pop, and Hard Rock, and Metal, and Electronica, and Reggae, and New Romantic, and Punk, and Grunge, and many many sub-categories of modern music.
Someone who likes rock? Let's call them a "rocker", that's a suitably non-committal term for someone who generally likes rock.