On Sat, Jun 15, 2019 at 04:18:21PM +0200, Ard Biesheuvel wrote: > Yes, I am using the same saturation point as x86. In this example, I > am not entirely sure I understand why it matters, though: the atomics > guarantee that the write by CPU2 fails if CPU1 changed the value in > the mean time, regardless of which value it wrote. > > I think the concern is more related to the likelihood of another CPU > doing something nasty between the moment that the refcount overflows > and the moment that the handler pins it at INT_MIN/2, e.g., > > > CPU 1 CPU 2 > > inc() > > load INT_MAX > > about to overflow? > > yes > > > > set to 0 > > <insert exploit here> > > set to INT_MIN/2
Ah, gotcha, but the "set to 0" is really "set to INT_MAX+1" (not zero) if you're using the same saturation. -- Kees Cook
