linux-kernel - Re: [PATCH 4/7] x86,nospec: Annotate indirect calls/jumps

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Date:   Thu, 1 Feb 2018 16:13:48 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>
Subject: Re: [PATCH 4/7] x86,nospec: Annotate indirect calls/jumps

On Thu, Feb 01, 2018 at 04:11:36PM +0100, Peter Zijlstra wrote:
> On Thu, Feb 01, 2018 at 02:55:26PM +0000, David Woodhouse wrote:
> > 
> > 
> > On Thu, 2018-02-01 at 15:34 +0100, Peter Zijlstra wrote:
> > > 
> > >   * These are the bare retpoline primitives for indirect jmp and call.
> > >   * Do not use these directly; they only exist to make the ALTERNATIVE
> > >   * invocation below less ugly.
> > > @@ -102,9 +114,9 @@
> > >  .macro JMP_NOSPEC reg:req
> > >  #ifdef CONFIG_RETPOLINE
> > >         ANNOTATE_NOSPEC_ALTERNATIVE
> > > -       ALTERNATIVE_2 __stringify(jmp *\reg),                           \
> > > +       ALTERNATIVE_2 __stringify(ANNOTATE_RETPOLINE_SAFE; jmp *\reg),  \
> > >                 __stringify(RETPOLINE_JMP \reg), X86_FEATURE_RETPOLINE, \
> > > -               __stringify(lfence; jmp *\reg), X86_FEATURE_RETPOLINE_AMD
> > > +               __stringify(lfence; ANNOTATE_RETPOLINE_SAFE; jmp *\reg), X86_FEATURE_RETPOLINE_AMD
> > >  #else
> > >         jmp     *\reg
> > >  #endif
> > 
> > The first one, yes. But the second one for the AMD retpoline is
> > redundant, isn't it? Objtool isn't going to look there.
> 
> It was when I wrote it.. lemme try again.

Insta complaint:

arch/x86/entry/.tmp_entry_64.o: warning: objtool: .altinstr_replacement+0x19: indirect jump found in RETPOLINE build