linux-kernel - Re: [PATCH v2 2/2] restrict /dev/mem to idle io memory ranges

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Message-ID: <CAGXu5j+N2o7UvLzq3Arw3zFEz1hLPEipcKu3RWyQ1m7BG0Ku=g@mail.gmail.com>
Date:	Tue, 24 Nov 2015 16:50:41 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-arch <linux-arch@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...hat.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 2/2] restrict /dev/mem to idle io memory ranges

On Tue, Nov 24, 2015 at 4:47 PM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Tue, 24 Nov 2015 16:34:19 -0800 Dan Williams <dan.j.williams@...el.com> wrote:
>
>> > IOW, a very good description of the problem-being-solved would help out
>> > a lot here...
>>
>> I'll fold the eventual result of this discussion into the changelog if
>> I can convince you it's worth moving forward.
>
> I'm easily convinced ;) Please let's get all the info into the right
> place, make sure it answers the thus-far-asked questions (at least) and
> we'll take it from there.
>
> And please do have a think about switching as much as possible over to
> runtime-configurability.  Because "please echo foo > /proc" is a heck
> of a lot nicer than "please reboot with iomem=" which is a heck of a lot
> nicer than "please ask vendor for a new kernel".

I think run-time config for this should be an as-needed case. Nothing
should be fiddling with this memory from userspace anyway -- a driver
covering it should be unloaded first.

And, with my dosemu maintainer hat on, If you're using dosemu in a
mode where this will cause a problem, you are already running a custom
kernel. :)

And that said, if someone can actually produce a case where we need
this runtime configurable, I'm all for it. I just don't think we need
to design it in right now.

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security
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