Re: [PATCH v3 01/10] mm: add Kernel Electric-Fence infrastructure

From: Marco Elver
Date: Fri Sep 25 2020 - 07:32:03 EST


On Fri, 25 Sep 2020 at 13:24, 'SeongJae Park' via kasan-dev
<kasan-dev@xxxxxxxxxxxxxxxx> wrote:
>
> On Mon, 21 Sep 2020 15:26:02 +0200 Marco Elver <elver@xxxxxxxxxx> wrote:
>
> > From: Alexander Potapenko <glider@xxxxxxxxxx>
> >
> > 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.
> >
> > 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. To detect out-of-bounds
> > writes to memory within the object's page itself, KFENCE also uses
> > pattern-based redzones. The following figure illustrates the page
> > layout:
> >
> > ---+-----------+-----------+-----------+-----------+-----------+---
> > | xxxxxxxxx | O : | xxxxxxxxx | : O | xxxxxxxxx |
> > | xxxxxxxxx | B : | xxxxxxxxx | : B | xxxxxxxxx |
> > | x GUARD x | J : RED- | x GUARD x | RED- : J | x GUARD x |
> > | xxxxxxxxx | E : ZONE | xxxxxxxxx | ZONE : E | xxxxxxxxx |
> > | xxxxxxxxx | C : | xxxxxxxxx | : C | xxxxxxxxx |
> > | xxxxxxxxx | T : | xxxxxxxxx | : T | xxxxxxxxx |
> > ---+-----------+-----------+-----------+-----------+-----------+---
> >
> > 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. To date, we have verified by running synthetic
> > benchmarks (sysbench I/O workloads) that a kernel compiled with KFENCE
> > is performance-neutral compared to the non-KFENCE baseline.
> >
> > For more details, see Documentation/dev-tools/kfence.rst (added later in
> > the series).
> >
> > Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> > Co-developed-by: Marco Elver <elver@xxxxxxxxxx>
> > Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
> > Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> > ---
> > v3:
> > * Reports by SeongJae Park:
> > * Remove reference to Documentation/dev-tools/kfence.rst.
> > * Remove redundant braces.
> > * Use CONFIG_KFENCE_NUM_OBJECTS instead of ARRAY_SIZE(...).
> > * Align some comments.
> > * Add figure from Documentation/dev-tools/kfence.rst added later in
> > series to patch description.
> >
> > v2:
> > * Add missing __printf attribute to seq_con_printf, and fix new warning.
> > [reported by kernel test robot <lkp@xxxxxxxxx>]
> > * Fix up some comments [reported by Jonathan Cameron].
> > * Remove 2 cases of redundant stack variable initialization
> > [reported by Jonathan Cameron].
> > * Fix printf format [reported by kernel test robot <lkp@xxxxxxxxx>].
> > * Print (in kfence-#nn) after address, to more clearly establish link
> > between first and second stacktrace [reported by Andrey Konovalov].
> > * Make choice between KASAN and KFENCE clearer in Kconfig help text
> > [suggested by Dave Hansen].
> > * Document CONFIG_KFENCE_SAMPLE_INTERVAL=0.
> > * Shorten memory corruption report line length.
> > * Make /sys/module/kfence/parameters/sample_interval root-writable for
> > all builds (to enable debugging, automatic dynamic tweaking).
> > * Reports by Dmitry Vyukov:
> > * Do not store negative size for right-located objects
> > * Only cache-align addresses of right-located objects.
> > * Run toggle_allocation_gate() after KFENCE is enabled.
> > * Add empty line between allocation and free stacks.
> > * Add comment about SLAB_TYPESAFE_BY_RCU.
> > * Also skip internals for allocation/free stacks.
> > * s/KFENCE_FAULT_INJECTION/KFENCE_STRESS_TEST_FAULTS/ as FAULT_INJECTION
> > is already overloaded in different contexts.
> > * Parenthesis for macro variable.
> > * Lower max of KFENCE_NUM_OBJECTS config variable.
> > ---
> > MAINTAINERS | 11 +
> > include/linux/kfence.h | 174 ++++++++++
> > init/main.c | 2 +
> > lib/Kconfig.debug | 1 +
> > lib/Kconfig.kfence | 63 ++++
> > mm/Makefile | 1 +
> > mm/kfence/Makefile | 3 +
> > mm/kfence/core.c | 733 +++++++++++++++++++++++++++++++++++++++++
> > mm/kfence/kfence.h | 102 ++++++
> > mm/kfence/report.c | 219 ++++++++++++
> > 10 files changed, 1309 insertions(+)
> > 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/report.c
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index b5cfab015bd6..863899ed9a29 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -9673,6 +9673,17 @@ F: include/linux/keyctl.h
> > F: include/uapi/linux/keyctl.h
> > F: security/keys/
> >
> > +KFENCE
> > +M: Alexander Potapenko <glider@xxxxxxxxxx>
> > +M: Marco Elver <elver@xxxxxxxxxx>
> > +R: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> > +L: kasan-dev@xxxxxxxxxxxxxxxx
> > +S: Maintained
> > +F: Documentation/dev-tools/kfence.rst
>
> This patch doesn't introduce this file yet, right? How about using a separate
> final patch for MAINTAINERS update?

Sure.

> Other than that,
>
> Reviewed-by: SeongJae Park <sjpark@xxxxxxxxx>

Thanks!