In October of last year Pershing Square, the hedge fund controlled by uber investor Bill Ackman, began gobbling up huge blocks of common stock in Fannie Mae and Freddie Mac at prices ranging from $1.54 to $2.27 a share. Today, a small portion of those positions is underwater, but thanks to a recent rebound in the stocks, whatever “paper” losses Pershing Square incurred have just about been wiped out. In trading Thursday, Fannie common was selling for $2.14, Freddie a few pennies below that.