The centre-back had been out of action since the end of 2012 after rupturing his anterior cruciate ligament, before suffering a recurrence of the injury last year.
However, the German international made his comeback on Friday as Bayern beat Red Barons fan club 3-0 in a pre-season clash.
"No, there was no doubt [that I might not return from injury]," he told the club's official website.
"I always knew I'd get a chance here, playing free of any pain. I always looked forward and was very focused. I don't make any demands [on my knee]. I enjoy every training session. Obviously I want to improve.
"I'm feeling good. If I look back over the last year, in comparison with today, I have made such big steps."
Badstuber has made close to 150 first-team appearances for Bayern.