Are you looking for songs sung traditionally BY prisoners, songs ABOUT prison experiences, both, or either?

My favorite song ABOUT prison is "Norwich Gaol", from Peter Bellamy's folk opera "The Transports". And as the theme of the opera is the transportation of convicts to Australia, other songs from it might fit your purposes.

The movie "Oh Brother, Where Art Thou" features:
"Po Lazarus" - sung by a prison gang as a work song; many work songs might be considered prison songs, too.
"Big Rock Candy Mountain" - a song about a prisoner dreaming of an idyllic place.
"I'll Fly Away" - one of Brumley's songs of inspiration, inspired by a prison song he heard a field laborer singing.
"In the Jailhouse Now" - need I comment?

"Ratcliffe Highway" involves imprisonment for desertion, two daring but failed escapes, and impending execution. Is that to your liking?