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Message-ID: <CAGXu5jJ64qCGuMCt+hTpwiVT+pu76b+g8QA=vtVgEv=a4ca9mQ@mail.gmail.com>
Date: Wed, 15 Jun 2016 10:05:49 -0700
From: Kees Cook <keescook@...omium.org>
To: Andy Lutomirski <luto@...capital.net>
Cc: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
Borislav Petkov <bp@...en8.de>, "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: Playing with virtually mapped stacks (with guard pages!)
On Tue, Jun 14, 2016 at 11:01 PM, Andy Lutomirski <luto@...capital.net> wrote:
> Hi all-
>
> If you want to play with virtually mapped stacks, I have it more or
> less working on x86 in a branch here:
>
> https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/log/?h=x86/vmap_stack
>
> The core bit (virtually map the stack and fix the accounting) is just
> a config option, but it needs the arch to opt-in. I suspect that
> every arch will have its own set of silly issues to address to make it
> work well. For x86, the silly issues are getting the OOPS to work
> right and handling some vmalloc_fault oddities to avoid panicing at
> random.
Awesome! Some notes/questions:
- there are a number of typos in commit messages and comments, just FYI
- where is the guard page added? I don't see anything leaving a hole at the end?
- where is thread_info? I understand there to be two benefits from
vmalloc stack: 1) thread_info can live elsewhere, 2) guard page can
exist easily
- this seems like it should Oops not warn:
WARN_ON_ONCE(vm->nr_pages != THREAD_SIZE / PAGE_SIZE);
that being wrong seems like a very bad state to continue from
- bikeshed: I think the CONFIG should live in arch/Kconfig (with a
description of what an arch needs to support for it) and be called
HAVE_ARCH_VMAP_STACK so that archs can select it instead of having
multiple definitions of CONFIG_VMAP_STACK in each arch.
Thanks for digging into this!
-Kees
--
Kees Cook
Chrome OS & Brillo Security
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