Any person who, while committing a crime of violence as defined in § 18.2-288 (2) or a felony violation of § 18.2-248 or subdivision (a) 2 or 3 of § 18.2-248.1, has in his possession a firearm or knife and is wearing body armor designed to diminish the effect of the impact of a bullet or projectile shall be guilty of a Class 4 felony.