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Date: Wed, 28 Mar 2018 22:57:06 +0300
From: Alexander Popov <alex.popov@...ux.com>
To: kernel-hardening@...ts.openwall.com,
	Kees Cook <keescook@...omium.org>,
	PaX Team <pageexec@...email.hu>,
	Brad Spengler <spender@...ecurity.net>,
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	x86@...nel.org,
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	alex.popov@...ux.com
Subject: [PATCH RFC v10 0/6] Introduce the STACKLEAK feature and a test for it

This is the 10th version of the patch series introducing STACKLEAK to the
mainline kernel. The previous version raised a fervent discussion[0].
The assembly code introduced by v9 irritated the reviewers.

I've found the way to bypass the obstacles[1] of the C implementation.
So I dare come once again. Let me ask you to look at this code without
preconception.

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.

 3. blocks stack depth overflow caused by alloca (aka Stack Clash attack).
    That is orthogonal to the mainline kernel VLA cleanup and protects
    un-upstreamed code.

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".

Links
=====

[0] http://www.openwall.com/lists/kernel-hardening/2018/03/03/7
[1] http://www.openwall.com/lists/kernel-hardening/2018/03/21/4


Alexander Popov (6):
  gcc-plugins: Clean up the cgraph_create_edge* macros
  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

 Documentation/security/self-protection.rst |  23 +-
 Documentation/x86/x86_64/mm.txt            |   2 +
 arch/Kconfig                               |  53 ++++
 arch/x86/Kconfig                           |   1 +
 arch/x86/entry/Makefile                    |   3 +
 arch/x86/entry/entry_32.S                  |  11 +
 arch/x86/entry/entry_64.S                  |  11 +
 arch/x86/entry/entry_64_compat.S           |  11 +
 arch/x86/entry/erase.c                     |  58 ++++
 arch/x86/include/asm/processor.h           |   7 +
 arch/x86/kernel/dumpstack.c                |  19 ++
 arch/x86/kernel/process_32.c               |   8 +
 arch/x86/kernel/process_64.c               |   8 +
 drivers/misc/Makefile                      |   3 +
 drivers/misc/lkdtm.h                       |   4 +
 drivers/misc/lkdtm_core.c                  |   2 +
 drivers/misc/lkdtm_stackleak.c             | 141 +++++++++
 fs/proc/base.c                             |  18 ++
 include/linux/compiler.h                   |   4 +
 mm/util.c                                  |  33 ++
 scripts/Makefile.gcc-plugins               |   3 +
 scripts/gcc-plugins/gcc-common.h           |  26 +-
 scripts/gcc-plugins/stackleak_plugin.c     | 470 +++++++++++++++++++++++++++++
 23 files changed, 900 insertions(+), 19 deletions(-)
 create mode 100644 arch/x86/entry/erase.c
 create mode 100644 drivers/misc/lkdtm_stackleak.c
 create mode 100644 scripts/gcc-plugins/stackleak_plugin.c

-- 
2.7.4

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