The most real prison songs are the songs made by prisoners, I suppose:-
https://www.musicbanter.com/country-...out-album.html
If that kind of hardcore
a capella material isn't to your liking, then the next most genuine article might be the concerts that Johnny Cash played in the Folsom and San Quentin prisons, which included several songs about prison life itself.
At a furthur remove are the artists who sing about prison without necessarily having been there. My two favourites are prob these wistful songs by The Allman Bros and Felice Bros :-
Finally, Exuma has a typically individualistic take on prison. Without researching, it seems to ref a real-life incident that led to imprisonment:-