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Date: Fri, 17 Aug 2018 01:16:57 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: kernel-hardening@...ts.openwall.com,
	Kees Cook <keescook@...omium.org>,
	PaX Team <pageexec@...email.hu>,
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	x86@...nel.org,
	linux-kernel@...r.kernel.org,
	alex.popov@...ux.com
Subject: [PATCH v15 0/7] Introduce the STACKLEAK feature and a test for it

This is the 15th version of the patch series introducing STACKLEAK to
the mainline kernel for x86. This version comes with changes according
to the feedback from Linus Torvalds:
 1. BUG_ON() in stackleak_erase() is safely eliminated;
 2. Stack Clash detection (alloca() check) is completely dropped, since global
    '-Wvla' should arrive soon (https://patchwork.kernel.org/patch/10489873).
    stackleak_check_alloca() for arm64 is dropped as well in a separate commit.

This version is rebased onto Linus' tree.

Previous version discussion:
  https://lore.kernel.org/lkml/20180813214328.GA15137@beast/T/#u

Motivation
==========

STACKLEAK (initially developed by PaX Team):

 1. reduces the information that can be revealed through kernel stack leak bugs.
    The idea of erasing the thread stack at the end of syscalls is similar to
    CONFIG_PAGE_POISONING and memzero_explicit() in kernel crypto, which all
    comply with FDP_RIP.2 (Full Residual Information Protection) of the
    Common Criteria standard.

 2. blocks some uninitialized stack variable attacks (e.g. CVE-2017-17712,
    CVE-2010-2963). That kind of bugs should be killed by improving C compilers
    in future, which might take a long time.

Performance impact
==================

Hardware: Intel Core i7-4770, 16 GB RAM

Test #1: building the Linux kernel on a single core
	0.91% slowdown

Test #2: hackbench -s 4096 -l 2000 -g 15 -f 25 -P
	4.2% slowdown

So the STACKLEAK description in Kconfig includes:
"The tradeoff is the performance impact: on a single CPU system kernel
compilation sees a 1% slowdown, other systems and workloads may vary and you are
advised to test this feature on your expected workload before deploying it".


Alexander Popov (7):
  x86/entry: Add STACKLEAK erasing the kernel stack at the end of
    syscalls
  gcc-plugins: Add STACKLEAK plugin for tracking the kernel stack
  lkdtm: Add a test for STACKLEAK
  fs/proc: Show STACKLEAK metrics in the /proc file system
  doc: self-protection: Add information about STACKLEAK feature
  stackleak: Allow runtime disabling of kernel stack erasing
  arm64: Drop unneeded stackleak_check_alloca()

 Documentation/security/self-protection.rst |  10 +-
 Documentation/sysctl/kernel.txt            |  18 ++
 Documentation/x86/x86_64/mm.txt            |   2 +
 arch/Kconfig                               |   7 +
 arch/arm64/kernel/process.c                |  22 --
 arch/x86/Kconfig                           |   1 +
 arch/x86/entry/calling.h                   |  14 +
 arch/x86/entry/entry_32.S                  |   7 +
 arch/x86/entry/entry_64.S                  |   3 +
 arch/x86/entry/entry_64_compat.S           |   5 +
 drivers/misc/lkdtm/Makefile                |   2 +
 drivers/misc/lkdtm/core.c                  |   1 +
 drivers/misc/lkdtm/lkdtm.h                 |   3 +
 drivers/misc/lkdtm/stackleak.c             |  73 +++++
 fs/proc/base.c                             |  18 ++
 include/linux/sched.h                      |   5 +
 include/linux/stackleak.h                  |  35 +++
 kernel/Makefile                            |   4 +
 kernel/fork.c                              |   3 +
 kernel/stackleak.c                         | 132 +++++++++
 kernel/sysctl.c                            |  15 +-
 scripts/Makefile.gcc-plugins               |  10 +
 scripts/gcc-plugins/Kconfig                |  51 ++++
 scripts/gcc-plugins/stackleak_plugin.c     | 427 +++++++++++++++++++++++++++++
 24 files changed, 840 insertions(+), 28 deletions(-)
 create mode 100644 drivers/misc/lkdtm/stackleak.c
 create mode 100644 include/linux/stackleak.h
 create mode 100644 kernel/stackleak.c
 create mode 100644 scripts/gcc-plugins/stackleak_plugin.c

-- 
2.7.4

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