Re: [tip:x86/pti] x86/retpoline: Fill return stack buffer on vmexit
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- Subject: Re: [tip:x86/pti] x86/retpoline: Fill return stack buffer on vmexit
- From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
- Date: Thu, 25 Jan 2018 10:56:46 -0600
- Cc: Borislav Petkov <bp@xxxxxxxxx>, tim.c.chen@xxxxxxxxxxxxxxx, pjt@xxxxxxxxxx, jikos@xxxxxxxxxx, gregkh@xxxxxxxxxxxxxxxxxxxx, dave.hansen@xxxxxxxxx, mingo@xxxxxxxxxx, riel@xxxxxxxxxx, luto@xxxxxxxxxxxxxx, torvalds@xxxxxxxxxxxxxxxxxxxx, ak@xxxxxxxxxxxxxxx, keescook@xxxxxxxxxx, peterz@xxxxxxxxxxxxx, tglx@xxxxxxxxxxxxx, hpa@xxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-tip-commits@xxxxxxxxxxxxxxx
- In-reply-to: <1516896198.30244.133.camel@infradead.org>
- References: <1515755487-8524-1-git-send-email-dwmw@amazon.co.uk> <tip-117cc7a908c83697b0b737d15ae1eb5943afe35b@git.kernel.org> <20180125120743.ey32gvl5mjam4r2s@pd.tnic> <1516882849.30244.94.camel@infradead.org> <20180125124554.vdx7rrnfrxrzl2ng@pd.tnic> <20180125151024.bidjr26r667vs7h5@treble> <20180125155110.mw655b7fwgm7qqc7@pd.tnic> <1516896198.30244.133.camel@infradead.org>
- User-agent: Mutt/1.6.0.1 (2016-04-01)
On Thu, Jan 25, 2018 at 04:03:18PM +0000, David Woodhouse wrote:
> 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.
Right, if you *really* want it always inline, the short term solution is
to just patch it in with X86_FEATURE_ALWAYS.
And don't ask me what the long term solution is, I don't even know what
I'm having for lunch today.
--
Josh
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