[PATCH v4 00/11] KFENCE: A low-overhead sampling-based memory safety error detector

Marco Elver
2020-09-29T13:40:31Z

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

v4:
* MAINTAINERS: Split out from first patch.
* Make static memory pool's attrs entirely arch-dependent.
* Fix report generation if __slab_free tail-called.
* Clarify RCU test comment [reported by Paul E. McKenney].

v3: https://lkml.kernel.org/r/20200921132611.1700350-1-elver@google.com
* 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@google.com
* 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 (5):
arm64, kfence: enable KFENCE for ARM64
kfence, lockdep: make KFENCE compatible with lockdep
kfence, Documentation: add KFENCE documentation
kfence: add test suite
MAINTAINERS: Add entry for KFENCE

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 | 783 +++++++++++++++++++++++++++++
mm/kfence/report.c | 225 +++++++++
mm/kmemleak.c | 6 +
mm/slab.c | 46 +-
mm/slab_common.c | 6 +-
mm/slub.c | 72 ++-
25 files changed, 2631 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

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