。
You have to follow the dormitory rules.
Literal
Dormitory [possessive-の] rules [topic-は] must-observe.
~なければならない (must do) is literally 'if one doesn't do X, it won't do' — a double-negative obligation pattern. 守る here means 'to observe/follow rules,' not 'to protect.' The subject is generic — the obligation applies to anyone in the dorm.