Re: [Security] proactive defense: using read-only memory, RO/NXmodules

From: Ingo Molnar
Date: Mon Nov 08 2010 - 01:13:47 EST

* Kees Cook <kees.cook@xxxxxxxxxxxxx> wrote:

> Hi,
> While Dan Rosenberg is working to make things harder to locate potential targets
> in the kernel through fixing kernel address leaks[1], I'd like to approach a
> related proactive security measure: enforcing read-only memory for things that
> would make good targets.

Nice! IMHO we need more of that. (If the readonly section gets big enough in
practice we could perhaps even mark it large-page in the future. It could serve as
an allocator to module code as well - that would probably be a speedup even for

> [...]
> The proposal is simple: as much of the kernel should be read-only as possible,
> most especially function pointers and other execution control points, which are
> the easiest target to exploit when an arbitrary kernel memory write becomes
> available[2] to an attacker. There has been past work to "const"ify function
> pointer tables, and this should continue. However, there are a few things that
> need further attention:
> - Modules need to be correctly marked RO/NX. This patch exists[3], but is
> not in mainline. It needs to be in mainline.
> [3];a=commitdiff;h=65187d24fa3ef60f691f847c792e8eaca7e19251

The reason the RO/NX patch from Siarhei Liakh is not upstream yet is rather mundane:
it introduced regressions - it caused boot crashes on one of my testboxes.

But there is no fundamental reason why it shouldnt be upstream. We can push it
upstream if the crashes are resolved and if it gets an Ack from Rusty or Linus for
the module bits.

Siarhei, what's the status of your RO/NX changes?


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