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

[Marco Elver]

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, a
guarded allocation from the KFENCE object pool is returned to the main
allocator (SLAB or SLUB). 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.

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

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 | 285 +++++++++++
 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                 |  70 +++
 mm/Makefile                        |   1 +
 mm/kasan/common.c                  |   7 +
 mm/kfence/Makefile                 |   6 +
 mm/kfence/core.c                   | 730 +++++++++++++++++++++++++++
 mm/kfence/kfence-test.c            | 777 +++++++++++++++++++++++++++++
 mm/kfence/kfence.h                 | 104 ++++
 mm/kfence/report.c                 | 201 ++++++++
 mm/kmemleak.c                      |  11 +
 mm/slab.c                          |  46 +-
 mm/slab_common.c                   |   6 +-
 mm/slub.c                          |  72 ++-
 25 files changed, 2591 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-test.c
 create mode 100644 mm/kfence/kfence.h
 create mode 100644 mm/kfence/report.c

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