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Date: Thu, 9 Mar 2017 09:31:52 -0800
From: Tycho Andersen <tycho@...ker.com>
To: Kees Cook <keescook@...omium.org>
Cc: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: Ahoy!
Hi Kees,
On Wed, Mar 8, 2017 at 10:01 PM, Kees Cook <keescook@...omium.org> wrote:
> On Wed, Mar 8, 2017 at 6:42 PM, Tycho Andersen <tycho@...ker.com> wrote:
> > Hey Kees,
> >
> > On Wed, Mar 08, 2017 at 03:17:55PM -0800, Kees Cook wrote:
> >> On Tue, Mar 7, 2017 at 3:37 PM, Tycho Andersen <tycho@...ker.com>
> wrote:
> >> > I'm a new engineer at Docker, and I've been given some time to work on
> >> > kernel security, so I figured I'd introduce myself here. I'm currently
> >> > trying to figure out what a good first small-ish project that matches
> up
> >> > with the company's interests (containers, infrastructure that is used
> for
> >> > security primitives like eBPF).
> >> >
> >> > Thoughts about areas to poke at are much appreciated!
> >>
> >> Hi! Welcome to the fun!
> >>
> >> As I understand it (for our earlier chat), Docker is mainly x86, which
> >> somewhat limits choices from the existing KSPP TODO list which has a
> >> lot of arm and arm64 stuff on it. :)
> >
> > Yes, unfortunately :(.
> >
> >> So, here's one that isn't protection exactly, but rather a requested
> >> arrangement of Kconfig logic: it would be nice if HARDENED_USERCOPY
> >> depended on !DEVKMEM and STRICT_DEVMEM=y, but this isn't quite trivial
> >> since STRICT_DEVMEM doesn't exist for all architectures, but maybe it
> >> should be looking at ARCH_HAS_DEVMEM_IS_ALLOWED... (it seems Dan
> >> Williams cleaned this up a lot already in commit 21266be9ed542)
> >>
> >> Regardless, no one has snagged this to make sure that hardened
> >> usercopy isn't bypassed by things like DEVKMEM or DEVMEM and the lack
> >> of STRICT_DEVMEM. I'd like to have that off the list, and mostly I
> >> think it just requires staring at the Kconfigs for a bit to figure out
> >> the right combination so that people wanting hardened usercopy don't
> >> accidentally undermine themselves.
> >
> > Yeah, I think it is fairly simple. Does the attached patch look like
> > what you had in mind? I can send out a real version to the right
> > people if it looks reasonable.
>
> Ah, I found the original thread.. https://lkml.org/lkml/2016/9/7/589
>
> Can you add the !MMU case, and then I think it'll be good.
>
Cool, I just sent it to both you and James, not sure exactly how it should
go.
>
> >> So, that's the first thing that pops out at me. What do you think? :)
> >
> > I was curious about PAX_MEMORY_STACKLEAK, actually. I noticed in the
> > initial KSPP announcement email you mentioned it, and it's not clear
> > to me that anything actually got merged for it.
>
> That was an example of one of the many plugins in grsecurity, but no
> one has looked at upstreaming it yet. Since we've got the gcc
> infrastructure in place now, yeah, please take a look; I'd love to add
> it.
> > I understand in principle what needs to happen, but I'm not sure I
> > understand why a gcc plugin is required.
>
> IIUC, the plugin is used to instrument the call depth so that it's an
> efficient clearing.
>
Ah, makes sense.
>
> > Anyway, it seems like a
> > small-ish change (that could be hid behind a sysctl or a compiler
> > flag) that is reasonable enough to start with. Thoughts?
>
> Nothing is ever simple. :) See the #ifdef CONFIG_PAX_MEMORY_STACKLEAK
> sections in the x86 entry code, fs/exec.c, etc. And it looks like
> additional changes (that lack the config ifdef in processor.h) for
> adding the new field to track depth, etc.
>
> (It'd be nice to expand this feature beyond x86 too, but that can be
> the next step.)
>
> As far as how to enable id, I would follow the existing Kconfig style
> (see how the structleak plugin was added for upstream).
>
Awesome, thanks for the pointers. I'll give it a whirl and see what I can
come up with.
Cheers,
Tycho
>
> I think it'd be a great addition!
>
> -Kees
>
> --
> Kees Cook
> Pixel Security
>
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