Can Exercise Be Performed If Suffering From Chondromalacia Patellae?

I had Chondromalacia patellae as a teen and needed to have a lateral release surgery. I've since had another surgery to clear up scar tissue. My knee doctor has told me that I have soft cartilage and should refrain from squats, lunges, and too many stairs. I have recently begun an exercise program and am unsure if I can kickbox or not with this particular problem. Also, on the treadmill, would I be able to do more than a fast walk?