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Date: Thu, 16 Jun 2016 10:24:24 -0700
From: Kees Cook <keescook@...omium.org>
To: Andy Lutomirski <luto@...nel.org>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>,
Borislav Petkov <bp@...en8.de>, Nadav Amit <nadav.amit@...il.com>, Brian Gerst <brgerst@...il.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Linus Torvalds <torvalds@...ux-foundation.org>, Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 00/13] Virtually mapped stacks with guard pages (x86, core)
On Wed, Jun 15, 2016 at 5:28 PM, Andy Lutomirski <luto@...nel.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
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