The focus ring itself has a little play, probably to allow for temperature expansion/contraction so it doesn't bind up. If you grip the red ring end with one hand and the camera mount end with the other and twist, turn and bend, there should be no movement at all between top and bottom.
That said, many Canon lenses do have a break zone in the middle that absorbs/deflects impact, along with the lens hood, should, for example, camera and lens on a tripod topple. The lens might even look broken in the middle, but I have seen this happen and the guy whose rig toppled popped it all back together and went on shooting.
So, if you do have play between the two halves, not just a little ring wiggle, better have it checked out