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

Ingo Molnar
2015-10-03T07:50:50Z

* Borislav Petkov <bp@alien8.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