mbox series

[v8,0/6] Optionally randomize kernel stack offset each syscall

Message ID 20210330205750.428816-1-keescook@chromium.org (mailing list archive)
Headers show
Series Optionally randomize kernel stack offset each syscall | expand

Message

Kees Cook March 30, 2021, 8:57 p.m. UTC 
v8:
- switch to __this_cpu_*() (tglx)
- improve commit log details, comments, and masking (ingo, tglx)
v7: https://lore.kernel.org/lkml/20210319212835.3928492-1-keescook@chromium.org/
v6: https://lore.kernel.org/lkml/20210315180229.1224655-1-keescook@chromium.org/
v5: https://lore.kernel.org/lkml/20210309214301.678739-1-keescook@chromium.org/
v4: https://lore.kernel.org/lkml/20200622193146.2985288-1-keescook@chromium.org/
v3: https://lore.kernel.org/lkml/20200406231606.37619-1-keescook@chromium.org/
v2: https://lore.kernel.org/lkml/20200324203231.64324-1-keescook@chromium.org/
rfc: https://lore.kernel.org/kernel-hardening/20190329081358.30497-1-elena.reshetova@intel.com/

Hi,

This is a continuation and refactoring of Elena's earlier effort to add
kernel stack base offset randomization. In the time since the earlier
discussions, two attacks[1][2] were made public that depended on stack
determinism, so we're no longer in the position of "this is a good idea
but we have no examples of attacks". :)

Earlier discussions also devolved into debates on entropy sources, which
is mostly a red herring, given the already low entropy available due
to stack size. Regardless, entropy can be changed/improved separately
from this series as needed.

Earlier discussions also got stuck debating how much syscall overhead
was too much, but this is also a red herring since the feature itself
needs to be selectable at boot with no cost for those that don't want it:
this is solved here with static branches.

So, here is the latest improved version, made as arch-agnostic as
possible, with usage added for x86 and arm64. It also includes some small
static branch clean ups, and addresses some surprise performance issues
due to the stack canary[3].

At the very least, the first two patches can land separately (already
Acked and Reviewed), since they're kind of "separate", but introduce
macros that are used in the core stack changes.

If I can get an Ack from an arm64 maintainer, I think this could all
land via -tip to make merging easiest.

Thanks!

-Kees

[1] https://a13xp0p0v.github.io/2020/02/15/CVE-2019-18683.html
[2] https://repositorio-aberto.up.pt/bitstream/10216/125357/2/374717.pdf
[3] https://lore.kernel.org/lkml/202003281520.A9BFF461@keescook/


Kees Cook (6):
  jump_label: Provide CONFIG-driven build state defaults
  init_on_alloc: Optimize static branches
  stack: Optionally randomize kernel stack offset each syscall
  x86/entry: Enable random_kstack_offset support
  arm64: entry: Enable random_kstack_offset support
  lkdtm: Add REPORT_STACK for checking stack offsets

 .../admin-guide/kernel-parameters.txt         | 11 ++++
 Makefile                                      |  4 ++
 arch/Kconfig                                  | 23 ++++++++
 arch/arm64/Kconfig                            |  1 +
 arch/arm64/kernel/Makefile                    |  5 ++
 arch/arm64/kernel/syscall.c                   | 16 ++++++
 arch/x86/Kconfig                              |  1 +
 arch/x86/entry/common.c                       |  3 +
 arch/x86/include/asm/entry-common.h           | 16 ++++++
 drivers/misc/lkdtm/bugs.c                     | 17 ++++++
 drivers/misc/lkdtm/core.c                     |  1 +
 drivers/misc/lkdtm/lkdtm.h                    |  1 +
 include/linux/jump_label.h                    | 19 +++++++
 include/linux/mm.h                            | 10 ++--
 include/linux/randomize_kstack.h              | 55 +++++++++++++++++++
 init/main.c                                   | 23 ++++++++
 mm/page_alloc.c                               |  4 +-
 mm/slab.h                                     |  6 +-
 18 files changed, 208 insertions(+), 8 deletions(-)
 create mode 100644 include/linux/randomize_kstack.h

Comments

Roy Yang April 1, 2021, 7:17 p.m. UTC | #1 
Both Android and Chrome OS really want this feature; For Container-Optimized OS, we have customers
interested in the defense too.

Thank you very much.

Change-Id: I1eb1b726007aa8f9c374b934cc1c690fb4924aa3
Al Viro April 1, 2021, 7:48 p.m. UTC | #2 
On Thu, Apr 01, 2021 at 12:17:44PM -0700, Roy Yang wrote:
> Both Android and Chrome OS really want this feature; For Container-Optimized OS, we have customers
> interested in the defense too.
> 
> Thank you very much.
> 
> Change-Id: I1eb1b726007aa8f9c374b934cc1c690fb4924aa3

	You forgot to tell what patch you are refering to.  Your
Change-Id (whatever the hell that is) doesn't help at all.  Don't
assume that keys in your internal database make sense for the
rest of the world, especially when they appear to contain a hash
of something...
Theodore Ts'o April 1, 2021, 8:13 p.m. UTC | #3 
On Thu, Apr 01, 2021 at 07:48:30PM +0000, Al Viro wrote:
> On Thu, Apr 01, 2021 at 12:17:44PM -0700, Roy Yang wrote:
> > Both Android and Chrome OS really want this feature; For Container-Optimized OS, we have customers
> > interested in the defense too.
> > 
> > Thank you very much.
> > 
> > Change-Id: I1eb1b726007aa8f9c374b934cc1c690fb4924aa3
> 
> 	You forgot to tell what patch you are refering to.  Your
> Change-Id (whatever the hell that is) doesn't help at all.  Don't
> assume that keys in your internal database make sense for the
> rest of the world, especially when they appear to contain a hash
> of something...

The Change-Id fails to have any direct search hits at lore.kernel.org.
However, it turn up Roy's original patch, and clicking on the
message-Id in the "In-Reply-Field", it apperas Roy was replying to
this message:

https://lore.kernel.org/lkml/20210330205750.428816-1-keescook@chromium.org/

which is the head of this patch series:

Subject: [PATCH v8 0/6] Optionally randomize kernel stack offset each syscall

That being said, it would have been better if the original subject
line had been preserved, and it's yet another example of how the
lore.kernel.org URL is infinitely better than the Change-Id.  :-)

		       		  	      - Ted
Kees Cook April 1, 2021, 9:46 p.m. UTC | #4 
On Thu, Apr 01, 2021 at 12:17:44PM -0700, Roy Yang wrote:
> Both Android and Chrome OS really want this feature; For Container-Optimized OS, we have customers
> interested in the defense too.

It's pretty close! There are a couple recent comments that need to be
addressed, but hopefully it can land if x86 and arm64 maintainers are
happy v10.

> Change-Id: I1eb1b726007aa8f9c374b934cc1c690fb4924aa3
> -- 
> 2.31.0.208.g409f899ff0-goog

And to let other folks know, I'm guessing this email got sent with git
send-email to try to get a valid In-Reply-To header, but I guess git
trashed the Subject and ran hooks to generate a Change-Id UUID.

I assume it's from following the "Reply instructions" at the bottom of:
https://lore.kernel.org/lkml/20210330205750.428816-1-keescook@chromium.org/
(It seems those need clarification about Subject handling.)