On Mon, 2018-01-08 at 15:56 -0800, Linus Torvalds wrote: > On Mon, Jan 8, 2018 at 3:44 PM, David Woodhouse <dw...@infradead.org> wrote: > > > > To guard against this fill the return buffer with controlled > > content during context switch. This prevents any underflows. > > Ugh. I really dislike this patch. Everything else in the retpoline > patches makes me go "ok, that's reasonable". This one makes me go > "Eww". > > It's hacky, it's ugly, and it looks pretty expensive too. > > Is there really nothing more clever we can do?
You get this part in the IBRS/microcode solution too. The IBRS MSR doesn't catch everything; you still need to stuff the RSB in very similar places (and/or use the IBPB MSR in some).
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