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SubjectRe: Improve retpoline for Skylake
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On Mon, 2018-01-15 at 10:06 -0800, Andy Lutomirski wrote:
>
> > Refill or not, you are aware that a correctly timed SMI in a leaf
> > function will cause the next ret to speculate into userspace, because
> > there is guaranteed peturbance in the RSB?  (On the expectation that the
> > SMM handler isn't entirely devoid of function calls).
>
> Couldn't firmware fill the RSB with a some known safe address, maybe
> even 0, and then immediately do RSM?

Why don't we just unconditionally declare that *all* firmware that uses
SMI for anything at all is broken?

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