OpenBSD: Theo de Raadt at CanSecWest: Synthetic Memory Protections
undeadly.org
undeadly.org
The idea that syscalls verify that stack pointer and PC are within valid regions at a first glance looks like a great idea, but I'm not sure if it stops many attacks. Might also turn out to be about too expensive...
You still need to go through the memory mappings every time, which is also randomised thanks to ASLR.