It's genuine, 'Star Wars' 1977 UK quad by Tom Chantrell, as I do not believe this poster has ever been faked. It looks to be in good rolled condition without fold lines too.
The only slightly bad news is that there are two versions of this poster, and this is the more common 'Oscars' version. That said, still a brilliant piece and worth £500 - £600 in my estimation. If you are going to sell probably easier to sell it unframed.