linux-kernel - Re: [PATCH v3 01/13] x86/retpoline: Add initial retpoline support

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Date:   Fri, 5 Jan 2018 14:03:58 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Juergen Gross <jgross@...e.com>
cc:     David Woodhouse <dwmw@...zon.co.uk>, ak@...ux.intel.com,
        Paul Turner <pjt@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Kees Cook <keescook@...gle.com>,
        Rik van Riel <riel@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>, gnomes@...rguk.ukuu.org.uk
Subject: Re: [PATCH v3 01/13] x86/retpoline: Add initial retpoline support

On Fri, 5 Jan 2018, Juergen Gross wrote:
> On 05/01/18 13:54, Thomas Gleixner wrote:
> > On Thu, 4 Jan 2018, David Woodhouse wrote:
> >> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> >> index 07cdd1715705..900fa7016d3f 100644
> >> --- a/arch/x86/include/asm/cpufeatures.h
> >> +++ b/arch/x86/include/asm/cpufeatures.h
> >> @@ -342,5 +342,6 @@
> >>  #define X86_BUG_MONITOR			X86_BUG(12) /* IPI required to wake up remote CPU */
> >>  #define X86_BUG_AMD_E400		X86_BUG(13) /* CPU is among the affected by Erratum 400 */
> >>  #define X86_BUG_CPU_INSECURE		X86_BUG(14) /* CPU is insecure and needs kernel page table isolation */
> >> +#define X86_BUG_NO_RETPOLINE		X86_BUG(15) /* Placeholder: disable retpoline branch thunks */
> > 
> > I think this is the wrong approach. We have X86_BUG_CPU_INSECURE, which now
> > should be renamed to X86_BUG_CPU_MELTDOWN_V3 or something like that. It
> > tells the kernel, that the CPU is affected by variant 3.
> 
> MELTDOWN is variant 3.
> 
> > 
> > If the kernel detects that and has PTI support then it sets the 'pti'
> > feature bit which tells that the mitigation is in place.
> > 
> > So what we really want is
> > 
> >    X86_BUG_MELTDOWN_V1/2/3
> 
> X86_BUG_MELTDOWN, X86_BUG_SPECTRE_V1, X86_BUG_SPECTRE_V2

Right. I'm confused as always :)