> > From: Theo de Raadt <dera...@cvs.openbsd.org> > > Date: Thu, 04 Jul 2013 09:04:54 -0600 > > > > I suspect the best approach would be a hybrid value. The upper half > > of the address should try to land in an unmapped zone, or into the zero > > page, or into some address space hole, ir into super high memory above > > the stack which is gauranteed unmapped. > > Don't forget strict alignment architectures, where it is beneficial > to have the lowest bit set to trigger alignment traps.
That's why I vaguely mentioned the idea of a sysctl or MD defines, which would declare a fixed component, plus a mask on top of random. That fixed component need not just be high bits, it can also cover the lowest bit (or two) for instance.