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

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Date:   Thu, 01 Feb 2018 14:55:26 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     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, 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.
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