The ref keep tracks of injury time, but it seldom adds up to the real time that is wasted.
I addition, time wasting in the form of diving and faking injuries chops up the flow of the game as well, making it harder for the attacking team.
Then in injury time, you can keep up the time wasting, and most of the time additional time will not be added.
SOunds like a flaw in the way the game is officiated. There should be penalties of some sort for diving and the clock should stop for injuries, real or fake. It's the subjectivity of the game that bothers me...