Gm Cm
-  -
3  3
3  4
3  5
5  5
5  3
3  3

 Pretty much those two chords, just strum them throughout the song.
 I do not know the first riff and some other assorted riffs throughout the song, but
this is the basic reggae strum that continues throughout the song, and I made this
tab...pretty much because it is my favorite song off of "Yours Truly" and nobody else 
had the tab and knew what the chords were, so here it is! Please Help yourself and jam away!