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

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Date:   Mon, 15 Jan 2018 08:48:12 -0800
From:   Andi Kleen <andi@...stfloor.org>
To:     David Laight <David.Laight@...LAB.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>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "arjan.van.de.ven@...el.com" <arjan.van.de.ven@...el.com>,
        "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

> It is not unlikely that most of a module's code is released as a
> binary 'blob', with only the part that needs to match the kernel ABI
> compiled on the target system.

Yes that is true. However such blob build systems are usually
done with custom Makefiles, not Kbuild, and those Makefiles don't set
-DRETPOLINE, so it would still be caught.

Now if someone sets -DRETPOLINE on a blob build it wouldn't warn,
but that would be actively malicious and there's no way to protect
against that.

It's merely aimed at detecting mistakes.

-Andi