Was the roll made using the SSME gimbal control? I would imagine the SRB does not have this capability. Is there any use of flight control surfaces as well?
Attitude control during first stage was achieved by SRB thrust vector control. The large distance between the nozzles and the high thrust levels meant that the SRB TVC had enormous control authority.
Bottom line: The roll program was performed by gimballing the SRB nozzles.