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Date:   Fri, 3 Apr 2020 11:16:07 -0500
From:   Josh Poimboeuf <jpoimboe@redhat.com>
To:     Alexandre Chartre <alexandre.chartre@oracle.com>
Cc:     x86@kernel.org, linux-kernel@vger.kernel.org, peterz@infradead.org,
        jthierry@redhat.com, tglx@linutronix.de
Subject: Re: [PATCH 5/7] x86/speculation: Annotate intra-function calls
Message-ID: <20200403161607.jxz6duaz7dud22wf@treble>
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 <20200402082220.808-6-alexandre.chartre@oracle.com>
 <20200403160538.qwu237amhanr6pyi@treble>
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On Fri, Apr 03, 2020 at 11:05:38AM -0500, Josh Poimboeuf wrote:
> On Thu, Apr 02, 2020 at 10:22:18AM +0200, Alexandre Chartre wrote:
> >  .macro RETPOLINE_JMP reg:req
> > -	call	.Ldo_rop_\@
> > +	INTRA_FUNCTION_CALL .Ldo_rop_\@
> >  .Lspec_trap_\@:
> >  	pause
> >  	lfence
> > @@ -102,7 +116,7 @@
> >  .Ldo_retpoline_jmp_\@:
> >  	RETPOLINE_JMP \reg
> >  .Ldo_call_\@:
> > -	call	.Ldo_retpoline_jmp_\@
> > +	INTRA_FUNCTION_CALL .Ldo_retpoline_jmp_\@
> >  .endm
> 
> There's a catch: this is part of an alternative.  Which means if
> X86_FEATURE_RETPOLINE isn't set at runtime, then the retpoline won't be
> there and the ORC data will be wrong.
> 
> In fact objtool should probably be made smart enough to warn about this
> situation, when an alternative changes the stack state.
> 
> The only way I can think of to fix this is to have ORC alternatives :-/

Or they could be converted to use static branches instead of
alternatives.

-- 
Josh