Re: [PATCH v6 11/10] x86/retpoline: Avoid return buffer underflows on context switch

[David Woodhouse]

On Mon, 2018-01-08 at 19:27 -0800, Andy Lutomirski wrote:
> >Â
> > If SMEP is not active, speculation can go anywhere, including to a user
> > controlled gadget which can reload any registers it needs, including
> > with immediate constants.
> 
> I thought that, even on pre-SMEP hardware, the CPU wouldn't
> speculatively execute from NX pages. And PTI marks user memory NX
> in kernel mode.

Hm, now that could be useful.Â

Do *all* the KPTI backports (some of which are reimplementations rather
than strictly backports) mark user memory NX?

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