On Mon, Jan 08, 2018 at 05:16:02PM -0800, Andi Kleen wrote: > > If we clear the registers, what the hell are you going to put in the > > RSB that helps you? > > RSB allows you to control chains of gadgets.
I admit the gadget thing is a bit obscure. There's another case we were actually more worried about: On Skylake and Broadwell when the RSB underflows it will fall back to the indirect branch predictor, which can be poisoned and we try to avoid using with retpoline. So we try to avoid underflows, and this filling helps us with that. Does that make more sense? -Andi
