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

[Kees Cook]

On Tue, Nov 24, 2015 at 4:47 PM, Andrew Morton
<akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Tue, 24 Nov 2015 16:34:19 -0800 Dan Williams <dan.j.williams@xxxxxxxxx> 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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