Re: [PATCH v2 00/10] KFENCE: A low-overhead sampling-based memory safety error detector

Dmitry Vyukov
2020-09-15T13:50:01Z

On Tue, Sep 15, 2020 at 3:20 PM Marco Elver <elver@google.com> 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.
>
> 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

I see all of my comments from v1 are resolved. So this is:

Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

for the series.

> v2:
> * 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@google.com
>
> 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
>
> --
> 2.28.0.618.gf4bc123cb7-goog
>