[$] A return-oriented programming defense from OpenBSD

Stack-smashing attacks have a long history; they featured, for example, asa core part of the Morris worm back in1988. Restrictions on executing code on the stack have, to a great extent,put an end to such simple attacks, but that does not mean thatstack-smashing attacks are no longer a threat. Return-orientedprogramming (ROP) has become a common technique for compromising systems via astack-smashing vulnerability. There are various schemes out there fordefeating ROP attacks, but a mechanism called "RETGUARD" that is being implementedin OpenBSD is notable for its relative simplicity.