lkml.org 
[lkml]   [2019]   [Feb]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [RFC PATCH 0/4] Allow tasks to have their user stack pointer sanity checked
On Mon, Feb 11, 2019 at 9:59 AM Will Deacon <will.deacon@arm.com> wrote:
>
> Hi all,
>
> I attended an interesting talk at LCA last month that described some of the
> security features deployed in OpenBSD [1]. One hardening feature that piqued
> my interest was, on syscall entry and page faults from userspace, checking
> that the user stack pointer for a task points at pages that were either
> allocated by the kernel for the initial process stack of mapped with mmap()
> using the MAP_STACK flag. This acts as a basic defense against stack
> pivoting attacks.

I think this is nice to have, yes! Thanks for working on it. It seems
like this blocks pivots to heap -- relocating to a groomed stack area
would still be allowed. Regardless, this does narrow the scope of such
attacks quite nicely.

> The problem with this checking is that it is a retrospective tightening
> of the ABI, but that hasn't stopped me hacking it together behind a couple
> of prctl() options.

MAP_STACK has been around for a long time, so I think anything using
threads via glibc should be "covered". I would assume this would mean
that glibc could set the prctl() for such users. I suspect there are a
lot of open-coded threading implementations, though. It'd be
interesting to see how many need modification.

Given that this is behind a prctl(), it seems the CONFIG isn't needed?

> Anyway, it was fun to implement so I figured I'd post it as an RFC.

Thanks! I'd love to see an x86 counterpart to the sycall check too.

Did you trying bringing up a full userspace and windowing environment
with this enabled by default (i.e. forcing init to set the prctls)?
I'd be curious to see how much (if anything) goes boom. :)

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

>
> Will
>
> [1] https://2019.linux.conf.au/schedule/presentation/164/
>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Jann Horn <jannh@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
>
> --->8
>
> Will Deacon (4):
> mm: Check user stack pointer is mapped with MAP_STACK
> mm: Expose user stack pointer checking via prctl()
> mm: Add kconfig entries for user stack pointer checking
> arm64: Check user stack pointer on syscall entry
>
> arch/arm64/Kconfig | 1 +
> arch/arm64/kernel/syscall.c | 4 +++
> include/linux/mm.h | 15 +++++++++-
> include/linux/mman.h | 3 +-
> include/linux/sched.h | 4 +++
> include/uapi/linux/prctl.h | 5 ++++
> kernel/sys.c | 5 ++++
> mm/Kconfig | 17 ++++++++++++
> mm/memory.c | 67 +++++++++++++++++++++++++++++++++++++++++++++
> 9 files changed, 119 insertions(+), 2 deletions(-)
>
> --
> 2.11.0
>


--
Kees Cook

\
 
 \ /
  Last update: 2019-02-11 20:13    [W:0.041 / U:0.368 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site