linux-kernel - Re: [PATCH 1/1] x86/speculation, objtool: Annotate indirect calls/jumps for objtool on 32bit

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Date:   Wed, 14 Mar 2018 13:24:06 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andy Whitcroft <apw@...onical.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] x86/speculation, objtool: Annotate indirect
 calls/jumps for objtool on 32bit


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Wed, Mar 14, 2018 at 11:24:27AM +0000, Andy Whitcroft wrote:
> > In 9e0e3c5130e9 ("x86/speculation, objtool: Annotate indirect calls/jumps
> > for objtool") we added annotations for CALL_NOSPEC/JMP_NOSPEC on x86 64bit.
> > We did not annotate the 32bit path.  Annotate it similarly.
> > 
> > Signed-off-by: Andy Whitcroft <apw@...onical.com>
> > ---
> >  arch/x86/include/asm/nospec-branch.h | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> >     While reviewing indirect calls in our builds I noted that the
> >     i386 retpoline CALL_NOSPEC is not annotated safe even though
> >     its amd64 equivalent is.  I cannot see any reason this is not
> >     also inherantly safe.  Peter was there a reason that you did
> >     not annotate this one too?  Anyhow, on the assumption this was
> >     just missed, this patch annotates it.
> 
> Yeah, just an oversight aided by the fact that I (obviously) never build
> 32bit kernels.
> 
> > diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
> > index d0dabeae0505..07886162bdf8 100644
> > --- a/arch/x86/include/asm/nospec-branch.h
> > +++ b/arch/x86/include/asm/nospec-branch.h
> > @@ -183,7 +183,10 @@
> >   * otherwise we'll run out of registers. We don't care about CET
> >   * here, anyway.
> >   */
> > -# define CALL_NOSPEC ALTERNATIVE("call *%[thunk_target]\n",	\
> > +# define CALL_NOSPEC 						\
> > +	ALTERNATIVE(						\
> > +	ANNOTATE_RETPOLINE_SAFE					\
> > +	"call *%[thunk_target]\n",				\
> >  	"       jmp    904f;\n"					\
> >  	"       .align 16\n"					\
> >  	"901:	call   903f;\n"					\
> 
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Applied, thanks guys!

	Ingo