linux-kernel - Re: [PATCH] retpoline/module: Taint kernel for missing retpoline in module

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Date:   Sat, 13 Jan 2018 16:37:57 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     "Van De Ven, Arjan" <arjan.van.de.ven@...el.com>
Cc:     Andi Kleen <andi@...stfloor.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "dwmw@...zon.co.uk" <dwmw@...zon.co.uk>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        Andi Kleen <ak@...ux.intel.com>,
        "jeyu@...nel.org" <jeyu@...nel.org>
Subject: Re: [PATCH] retpoline/module: Taint kernel for missing retpoline in
 module

On Sat, Jan 13, 2018 at 02:38:51PM +0000, Van De Ven, Arjan wrote:
> > > When the a module hasn't been compiled with a retpoline
> > > aware compiler, print a warning and set a taint flag.
> > 
> > Isn't that caught by the "build with a different compiler/version" check
> > that we have?  Or used to have?  If not, can't we just make it into that
> > type of check to catch this type of problem no matter what type of
> > feature/option it is trying to catch?
> 
> 
> making retpoline part of the modversion hash thingy could make sense.
> 
> but I kinda feel this is a bit overkill; it's not a function issue if
> you get this wrong, and if you run an ancient or weird out of tree
> module there's a real chance you have other security fun as well ;-)

Sure, but take pity on the crazy distro developers who have to support
crap like this.  They really want to know if a module is built
differently from the kernel, to force the user to know they are on their
own.

modversion seems like a trivial thing to mix this into, and solves the
distro issue at the same time.

thanks,

greg k-h