linux-kernel - Re: [PATCH 5.18 34/61] objtool: Update Retpoline validation

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Message-ID: <Ys6OiDQCuP072GCX@nazgul.tnic>
Date:   Wed, 13 Jul 2022 11:21:30 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jiri Slaby <jirislaby@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Subject: Re: [PATCH 5.18 34/61] objtool: Update Retpoline validation

On Wed, Jul 13, 2022 at 10:17:54AM +0200, Greg Kroah-Hartman wrote:
> > A naive fix is:
> > --- a/arch/x86/kernel/head_32.S
> > +++ b/arch/x86/kernel/head_32.S
> > @@ -23,6 +23,7 @@
> >  #include <asm/cpufeatures.h>
> >  #include <asm/percpu.h>
> >  #include <asm/nops.h>
> > +#include <asm/nospec-branch.h>
> >  #include <asm/bootparam.h>
> >  #include <asm/export.h>
> >  #include <asm/pgtable_32.h>

Yap, pls send a proper patch.

> I doubt it should be doing that, but I'll let others answer more
> definitively.

I'd leave that question to the objtool folks.

Technically, the UNTRAIN_RET sequence is meant for both 32- and 64-bit
so there should be no reason not to mitigate that on 32-bit too. Not
that people should run 32-bit kernels...

> Your commit seems sane, for some reason I thought Boris tested i386
> builds, but maybe in the end something snuck in that broke it.

I caught one build breakage in relocate_kernel_32.S but this is a new
one.

Thx.

-- 
Regards/Gruss,
    Boris.

SUSE Software Solutions Germany GmbH
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Martje Boudien Moerman
(HRB 36809, AG Nürnberg)