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 >
