Re: [PATCH 00/13] Virtually mapped stacks with guard pages (x86, core)

[Kees Cook <keescook@chromium.org>]

On Wed, Jun 15, 2016 at 5:28 PM, Andy Lutomirski <luto@kernel.org> wrote:
> Since the dawn of time, a kernel stack overflow has been a real PITA
> to debug, has caused nondeterministic crashes some time after the
> actual overflow, and has generally been easy to exploit for root.
>
> With this series, arches can enable HAVE_ARCH_VMAP_STACK.  Arches
> that enable it (just x86 for now) get virtually mapped stacks with
> guard pages.  This causes reliable faults when the stack overflows.
>
> If the arch implements it well, we get a nice OOPS on stack overflow
> (as opposed to panicing directly or otherwise exploding badly).  On
> x86, the OOPS is nice, has a usable call trace, and the overflowing
> task is killed cleanly.
>
> This does not address interrupt stacks.
>
> Andy Lutomirski (12):
>   x86/cpa: In populate_pgd, don't set the pgd entry until it's populated
>   x86/cpa: Warn if kernel_unmap_pages_in_pgd is used inappropriately
>   mm: Track NR_KERNEL_STACK in pages instead of number of stacks
>   mm: Move memcg stack accounting to account_kernel_stack
>   fork: Add generic vmalloced stack support
>   x86/die: Don't try to recover from an OOPS on a non-default stack
>   x86/dumpstack: When OOPSing, rewind the stack before do_exit
>   x86/dumpstack: When dumping stack bytes due to OOPS, start with
>     regs->sp
>   x86/dumpstack: Try harder to get a call trace on stack overflow
>   x86/dumpstack/64: Handle faults when printing the "Stack:" part of an
>     OOPS
>   x86/mm/64: Enable vmapped stacks
>   x86/mm: Improve stack-overflow #PF handling
>
> Ingo Molnar (1):
>   x86/mm/hotplug: Don't remove PGD entries in remove_pagetable()
>
>  arch/Kconfig                     | 12 ++++++++++
>  arch/x86/Kconfig                 |  1 +
>  arch/x86/entry/entry_32.S        | 11 +++++++++
>  arch/x86/entry/entry_64.S        | 11 +++++++++
>  arch/x86/include/asm/switch_to.h | 28 +++++++++++++++++++++-
>  arch/x86/include/asm/traps.h     |  6 +++++
>  arch/x86/kernel/dumpstack.c      | 17 +++++++++++++-
>  arch/x86/kernel/dumpstack_32.c   |  4 +++-
>  arch/x86/kernel/dumpstack_64.c   | 16 ++++++++++---
>  arch/x86/kernel/traps.c          | 32 +++++++++++++++++++++++++
>  arch/x86/mm/fault.c              | 39 ++++++++++++++++++++++++++++++
>  arch/x86/mm/init_64.c            | 27 ---------------------
>  arch/x86/mm/pageattr.c           |  7 +++++-
>  arch/x86/mm/tlb.c                | 15 ++++++++++++
>  fs/proc/meminfo.c                |  2 +-
>  kernel/fork.c                    | 51 ++++++++++++++++++++++++++++++----------
>  mm/page_alloc.c                  |  3 +--
>  17 files changed, 233 insertions(+), 49 deletions(-)

This is great, thanks! This helps the up-coming usercopy
self-protection code, and makes stack overflows a much less
interesting target for attackers.

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security