‘Looper’ Trailer: What’d They Do to JGL’s Face?

Here's a trailer for what looks like a pretty good action movie called Looper, starring Bruce Willis and Joseph Gordon Levitt as older/younger versions of each other. It looks like they went to some pretty great lengths to make "JGL" look like Willis, but I can't put my finger on exactly what they did...

See what I mean? Is it makeup, CGI, or does JGL just do a really good Bruce Willis impression?