linux-kernel - Re: [PATCH v8 04/12] x86/spectre: Add boot time option to select Spectre v2 mitigation

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Message-ID: <nycvar.YFH.7.76.1801241500140.11852@cbobk.fhfr.pm>
Date:   Wed, 24 Jan 2018 15:03:48 +0100 (CET)
From:   Jiri Kosina <jikos@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...ux-foundation.org>
cc:     Andi Kleen <ak@...ux.intel.com>, Borislav Petkov <bp@...en8.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Paul Turner <pjt@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kees Cook <keescook@...gle.com>,
        Rik van Riel <riel@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        gnomes@...rguk.ukuu.org.uk, x86@...nel.org,
        thomas.lendacky@....com, Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH v8 04/12] x86/spectre: Add boot time option to select
 Spectre v2 mitigation

On Wed, 24 Jan 2018, Greg Kroah-Hartman wrote:

> > > I just thought since you were already using modversions in enterprise 
> > > distros already, that adding it there would be the simplest.
> > 
> > The patch as-is introduces immediate modversion mismatch between 
> > retpolined kernel and non-retpolined module, making each and every one 
> > fail to load.
> 
> Good, the patch works then, because I thought that not loading
> non-retpolined modules in a kernel that was built with retpoline was the
> goal here.

No, we do not want to break loading of externally-built modules just 
because they might contain indirect calls.

Warning in such situations / tainting the kernel / reporting "might be 
vulnerable" in sysfs should be the proper way to go.

retpolines are not kernel ABI (towards modules) breaker, so let's not 
pretend it is.

Thanks,

-- 
Jiri Kosina
SUSE Labs