Re: [PATCH v11 0/6] Introduce the STACKLEAK feature and a test for it

[Laura Abbott <labbott@redhat.com>]

On 04/06/2018 07:22 AM, Alexander Popov wrote:
> This is the 11th version of the patch series introducing STACKLEAK to the
> mainline kernel. The 9th version raised a fervent discussion[0].
> The assembly code introduced by that version irritated the reviewers.
> 
> I've found the way to bypass the obstacles[1] of the C implementation.
> So I dare come 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/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 +
>   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 +++++++++++++++++++++++++++++
>   24 files changed, 896 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
> 

As a point of reference, this series mitigates the leak
fixed by https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0a0b98734479aa5b3c671d5190e86273372cab95

Thanks,
Laura