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

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Message-ID: <20180124142213.GA11440@kroah.com>
Date:   Wed, 24 Jan 2018 15:22:13 +0100
From:   Greg Kroah-Hartman <gregkh@...ux-foundation.org>
To:     Jiri Kosina <jikos@...nel.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, Jan 24, 2018 at 03:03:48PM +0100, Jiri Kosina wrote:
> 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.

Ok, my fault, I should not have suggested that Andi do the check this
way then.  I thought we wanted to make this part of the kernel ABI.

I'll go make up a patch to revert this now...

thanks,

greg k-h