Re: [PATCH v3 00/10] KFENCE: A low-overhead sampling-based memory safety error detector

[Dmitry Vyukov]

On Mon, Sep 21, 2020 at 3:26 PM Marco Elver <elver@xxxxxxxxxx> wrote:
>
> This adds the Kernel Electric-Fence (KFENCE) infrastructure. KFENCE is a
> low-overhead sampling-based memory safety error detector of heap
> use-after-free, invalid-free, and out-of-bounds access errors.  This
> series enables KFENCE for the x86 and arm64 architectures, and adds
> KFENCE hooks to the SLAB and SLUB allocators.

Hi Andrew,

I wanted to ask what we can expect with respect to the timeline of
merging this into mm/upstream? The series got few reviews/positive
feedback.

Thank you



> KFENCE is designed to be enabled in production kernels, and has near
> zero performance overhead. Compared to KASAN, KFENCE trades performance
> for precision. The main motivation behind KFENCE's design, is that with
> enough total uptime KFENCE will detect bugs in code paths not typically
> exercised by non-production test workloads. One way to quickly achieve a
> large enough total uptime is when the tool is deployed across a large
> fleet of machines.
>
> KFENCE objects each reside on a dedicated page, at either the left or
> right page boundaries. The pages to the left and right of the object
> page are "guard pages", whose attributes are changed to a protected
> state, and cause page faults on any attempted access to them. Such page
> faults are then intercepted by KFENCE, which handles the fault
> gracefully by reporting a memory access error.
>
> Guarded allocations are set up based on a sample interval (can be set
> via kfence.sample_interval). After expiration of the sample interval,
> the next allocation through the main allocator (SLAB or SLUB) returns a
> guarded allocation from the KFENCE object pool. At this point, the timer
> is reset, and the next allocation is set up after the expiration of the
> interval.
>
> To enable/disable a KFENCE allocation through the main allocator's
> fast-path without overhead, KFENCE relies on static branches via the
> static keys infrastructure. The static branch is toggled to redirect the
> allocation to KFENCE.
>
> The KFENCE memory pool is of fixed size, and if the pool is exhausted no
> further KFENCE allocations occur. The default config is conservative
> with only 255 objects, resulting in a pool size of 2 MiB (with 4 KiB
> pages).
>
> We have verified by running synthetic benchmarks (sysbench I/O,
> hackbench) that a kernel with KFENCE is performance-neutral compared to
> a non-KFENCE baseline kernel.
>
> KFENCE is inspired by GWP-ASan [1], a userspace tool with similar
> properties. The name "KFENCE" is a homage to the Electric Fence Malloc
> Debugger [2].
>
> For more details, see Documentation/dev-tools/kfence.rst added in the
> series -- also viewable here:
>
>         https://raw.githubusercontent.com/google/kasan/kfence/Documentation/dev-tools/kfence.rst
>
> [1] http://llvm.org/docs/GwpAsan.html
> [2] https://linux.die.net/man/3/efence
>
> v3:
> * Rewrite SLAB/SLUB patch descriptions to clarify need for 'orig_size'.
> * Various smaller fixes (see details in patches).
>
> v2: https://lkml.kernel.org/r/20200915132046.3332537-1-elver@xxxxxxxxxx
> * Various comment/documentation changes (see details in patches).
> * Various smaller fixes (see details in patches).
> * Change all reports to reference the kfence object, "kfence-#nn".
> * Skip allocation/free internals stack trace.
> * Rework KMEMLEAK compatibility patch.
>
> RFC/v1: https://lkml.kernel.org/r/20200907134055.2878499-1-elver@xxxxxxxxxx
>
> Alexander Potapenko (6):
>   mm: add Kernel Electric-Fence infrastructure
>   x86, kfence: enable KFENCE for x86
>   mm, kfence: insert KFENCE hooks for SLAB
>   mm, kfence: insert KFENCE hooks for SLUB
>   kfence, kasan: make KFENCE compatible with KASAN
>   kfence, kmemleak: make KFENCE compatible with KMEMLEAK
>
> Marco Elver (4):
>   arm64, kfence: enable KFENCE for ARM64
>   kfence, lockdep: make KFENCE compatible with lockdep
>   kfence, Documentation: add KFENCE documentation
>   kfence: add test suite
>
>  Documentation/dev-tools/index.rst  |   1 +
>  Documentation/dev-tools/kfence.rst | 291 +++++++++++
>  MAINTAINERS                        |  11 +
>  arch/arm64/Kconfig                 |   1 +
>  arch/arm64/include/asm/kfence.h    |  39 ++
>  arch/arm64/mm/fault.c              |   4 +
>  arch/x86/Kconfig                   |   2 +
>  arch/x86/include/asm/kfence.h      |  60 +++
>  arch/x86/mm/fault.c                |   4 +
>  include/linux/kfence.h             | 174 +++++++
>  init/main.c                        |   2 +
>  kernel/locking/lockdep.c           |   8 +
>  lib/Kconfig.debug                  |   1 +
>  lib/Kconfig.kfence                 |  78 +++
>  mm/Makefile                        |   1 +
>  mm/kasan/common.c                  |   7 +
>  mm/kfence/Makefile                 |   6 +
>  mm/kfence/core.c                   | 733 +++++++++++++++++++++++++++
>  mm/kfence/kfence.h                 | 102 ++++
>  mm/kfence/kfence_test.c            | 777 +++++++++++++++++++++++++++++
>  mm/kfence/report.c                 | 219 ++++++++
>  mm/kmemleak.c                      |   6 +
>  mm/slab.c                          |  46 +-
>  mm/slab_common.c                   |   6 +-
>  mm/slub.c                          |  72 ++-
>  25 files changed, 2619 insertions(+), 32 deletions(-)
>  create mode 100644 Documentation/dev-tools/kfence.rst
>  create mode 100644 arch/arm64/include/asm/kfence.h
>  create mode 100644 arch/x86/include/asm/kfence.h
>  create mode 100644 include/linux/kfence.h
>  create mode 100644 lib/Kconfig.kfence
>  create mode 100644 mm/kfence/Makefile
>  create mode 100644 mm/kfence/core.c
>  create mode 100644 mm/kfence/kfence.h
>  create mode 100644 mm/kfence/kfence_test.c
>  create mode 100644 mm/kfence/report.c
>
> --
> 2.28.0.681.g6f77f65b4e-goog
>