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

[Marco Elver]

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!