linux-kernel - Re: [RFC][PATCH] x86/mm: warn on W+x mappings

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Message-ID: <20151003075045.GC25143@gmail.com>
Date:	Sat, 3 Oct 2015 09:50:45 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Kees Cook <keescook@...omium.org>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	"x86@...nel.org" <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH] x86/mm: warn on W+x mappings


* Borislav Petkov <bp@...en8.de> wrote:

> On Fri, Oct 02, 2015 at 09:26:44AM +0200, Ingo Molnar wrote:
> > It's better to generate a WARN()ing programmatically if the W+X condition occurs, 
> > that gets noticed by tools and people alike. I'd like to start treating that 
> > condition as a hard kernel bug.
> > 
> > A dump in dmesg is subject to random noise by printk crusaders and is also subject 
> > to general bitrot, nor does it provide any ready warning to act upon.
> 
> You're not going to enable this option in production anyway. [...]

Why not? I'd suggest distros do it too, it's not too much code to run during 
bootup. That way if we one some weird configuration forget about a W+X mapping, 
the distro is warned that there's a security problem.

> > I'd even add this debug check as default-enabled in the x86 defconfigs, so 
> > that my own continuous kernel testing kit picks up any new warnings from it.
> 
> There's the problem with exposing sensitive info in debugfs if you do that. And 
> nowadays we're trying hard not to leak any of that.

Ah, I think you missed the following detail: the patch I suggested would separate 
the debugfs bits from the checking bits and would thus allow a 'security check 
only' .config setting.

Distros would normally not want to enable the debugfs file, agreed about that.

Thanks,

	Ingo
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