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From: Kees Cook <>
To: Thomas Gleixner <>
Cc: Kees Cook <>,
	Elena Reshetova <>,, Andy Lutomirski <>,
	Peter Zijlstra <>,
	Catalin Marinas <>,
	Will Deacon <>,
	Mark Rutland <>,
	Alexander Potapenko <>,
	Ard Biesheuvel <>,
	Jann Horn <>,,,,
Subject: [PATCH v3 0/5] Optionally randomize kernel stack offset each syscall
Date: Mon,  6 Apr 2020 16:16:01 -0700
Message-ID: <> (raw)

- added review/ack tags (peterz, glider)
- further clarified commit logs and public attack references
- added -fstack-protector downgrades and details


This is a continuation and refactoring of Elena's earlier effort to add
kernel stack base offset randomization. In the time since the previous
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 an 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 (5):
  jump_label: Provide CONFIG-driven build state defaults
  init_on_alloc: Unpessimize default-on builds
  stack: Optionally randomize kernel stack offset each syscall
  x86/entry: Enable random_kstack_offset support
  arm64: entry: Enable random_kstack_offset support

 Makefile                         |  4 ++++
 arch/Kconfig                     | 23 ++++++++++++++++++
 arch/arm64/Kconfig               |  1 +
 arch/arm64/kernel/Makefile       |  4 ++++
 arch/arm64/kernel/syscall.c      | 10 ++++++++
 arch/x86/Kconfig                 |  1 +
 arch/x86/entry/Makefile          |  9 +++++++
 arch/x86/entry/common.c          | 12 +++++++++-
 include/linux/jump_label.h       | 19 +++++++++++++++
 include/linux/mm.h               | 18 +++++---------
 include/linux/randomize_kstack.h | 40 ++++++++++++++++++++++++++++++++
 init/main.c                      | 23 ++++++++++++++++++
 mm/page_alloc.c                  | 12 ++--------
 13 files changed, 153 insertions(+), 23 deletions(-)
 create mode 100644 include/linux/randomize_kstack.h


             reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-06 23:16 Kees Cook [this message]
2020-04-06 23:16 ` [PATCH v3 1/5] jump_label: Provide CONFIG-driven build state defaults Kees Cook
2020-04-06 23:16 ` [PATCH v3 2/5] init_on_alloc: Unpessimize default-on builds Kees Cook
2020-04-06 23:16 ` [PATCH v3 3/5] stack: Optionally randomize kernel stack offset each syscall Kees Cook
2020-04-06 23:16 ` [PATCH v3 4/5] x86/entry: Enable random_kstack_offset support Kees Cook
2020-04-06 23:16 ` [PATCH v3 5/5] arm64: entry: " Kees Cook

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