[gamblor956]

Tom Cruise actually performed that stunt. There is a highlight BTS reel showing how they composited that shot (https://www.youtube.com/watch?v=eZjsZCMBT-s one of several; just the first result in my Google search). As you can see, he's very well secured to the plane in the BTS footage; the cables and other protection are composited out in post-production. Similarly, in the water tank scene later in the movie, Cruise actually jumped 120 feet into water, and held his breath in a water tank for several minutes (though the fountain in the jump, and the arm in the tank were both composited into the scene in post).

In fact, Tom Cruise actually performs most of his stunts, especially for the MI movies. It's kind of his thing; while the context of the stunt might be CGI the action itself is real.

He's worth more than a billion dollars, so he can afford to pay specialists to train him; he supposedly spent over a year learning to hold his breath for several minutes just for the water tank scene.