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Date: Wed, 31 Mar 2021 13:54:52 -0700
From: Kees Cook <>
To: Will Deacon <>
Cc: Kees Cook <>,
	Catalin Marinas <>,
	Mark Rutland <>,
	Thomas Gleixner <>,
	Elena Reshetova <>,,
	Andy Lutomirski <>,
	Peter Zijlstra <>,
	Alexander Potapenko <>,
	Alexander Popov <>,
	Ard Biesheuvel <>,
	Jann Horn <>,
	Vlastimil Babka <>,
	David Hildenbrand <>,
	Mike Rapoport <>,
	Andrew Morton <>,
	Jonathan Corbet <>,
	Randy Dunlap <>,,,,,
Subject: [PATCH v9 0/6] Optionally randomize kernel stack offset each syscall

Hi Will (and Mark and Catalin),

Can you take this via the arm64 tree for v5.13 please? Thomas has added
his Reviewed-by, so it only leaves arm64's. :)

- comment position nit (tglx)
- Added tglx's Reviewed-by

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].




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              | 54 +++++++++++++++++++
 init/main.c                                   | 23 ++++++++
 mm/page_alloc.c                               |  4 +-
 mm/slab.h                                     |  6 ++-
 18 files changed, 207 insertions(+), 8 deletions(-)
 create mode 100644 include/linux/randomize_kstack.h


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