The BASE jumps were for real and the crew filmed 10 of then to get the shots they needed as well as an additional 20 jumps from a helicopter to grab some of the high level wing-suit flying. Anyway, there is a great BTS video here shot by Michael Nordqvist who also filmed the high level stuff - although I have to say there are definitely a few shots that look to have been digitally manipulated in order to get the characters to do very sharp mid-air turns to avoid buildings. Still it's an impressive stunt set piece and worth looking at because it also shows us the 2IFC prior to completion.
Heading up to the top
In the picture above, you can see how high the jumpers had to get in the helicopter. At this point they look to be double the real height of the 2IFC and there is a small sequence in the above linked video that shows you a similar height and angle. The next picture shows the section of the wing suit flight that looks to be digitally manipulated and includes a close bypass of the BOC tower before a sharp left hand turn to avoid the Lippo Centre.
And a boat landing to finish it all off.