Re: [tip:x86/pti] x86/retpoline: Fill return stack buffer on vmexit

[David Woodhouse]

On Thu, 2018-01-25 at 16:51 +0100, Borislav Petkov wrote:
> 
> > And the seg fault is objtool's way of telling you you need a
> > ANNOTATE_NOSPEC_ALTERNATIVE above the alternative ;-)
> 
> Except that it blew up when I did this which doesn't have ALTERNATIVE
> (it's the diff I saved :-))

Yeah, ANNOTATE_NOSPEC_ALTERNATIVE just tells objtool "don't look at the
alternative; you're not going to like it".

If you start putting a __fill_rsb() function out of line somewhere and
only *calling* it from alternatives, then objtool is going to shit
itself when it sees that function, regardless.

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