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authorAlexander Potapenko <glider@google.com>2021-02-25 17:18:53 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2021-02-26 09:41:02 -0800
commit0ce20dd840897b12ae70869c69f1ba34d6d16965 (patch)
tree9fad86c287a99f5e91a14736b512d5e0fb053958 /lib
parent87005394e14aa2f886581fb51e5e2022dc77ea05 (diff)
mm: add Kernel Electric-Fence infrastructure
Patch series "KFENCE: A low-overhead sampling-based memory safety error detector", v7. 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) and production server-workload benchmarks that a kernel with KFENCE (using sample intervals 100-500ms) 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 This patch (of 9): 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, hackbench) 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). [elver@google.com: fix parameter description for kfence_object_start()] Link: https://lkml.kernel.org/r/20201106092149.GA2851373@elver.google.com [elver@google.com: avoid stalling work queue task without allocations] Link: https://lkml.kernel.org/r/CADYN=9J0DQhizAGB0-jz4HOBBh+05kMBXb4c0cXMS7Qi5NAJiw@mail.gmail.com Link: https://lkml.kernel.org/r/20201110135320.3309507-1-elver@google.com [elver@google.com: fix potential deadlock due to wake_up()] Link: https://lkml.kernel.org/r/000000000000c0645805b7f982e4@google.com Link: https://lkml.kernel.org/r/20210104130749.1768991-1-elver@google.com [elver@google.com: add option to use KFENCE without static keys] Link: https://lkml.kernel.org/r/20210111091544.3287013-1-elver@google.com [elver@google.com: add missing copyright and description headers] Link: https://lkml.kernel.org/r/20210118092159.145934-1-elver@google.com Link: https://lkml.kernel.org/r/20201103175841.3495947-2-elver@google.com Signed-off-by: Marco Elver <elver@google.com> Signed-off-by: Alexander Potapenko <glider@google.com> Reviewed-by: Dmitry Vyukov <dvyukov@google.com> Reviewed-by: SeongJae Park <sjpark@amazon.de> Co-developed-by: Marco Elver <elver@google.com> Reviewed-by: Jann Horn <jannh@google.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Paul E. McKenney <paulmck@kernel.org> Cc: Andrey Konovalov <andreyknvl@google.com> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christopher Lameter <cl@linux.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: David Rientjes <rientjes@google.com> Cc: Eric Dumazet <edumazet@google.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Hillf Danton <hdanton@sina.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Joern Engel <joern@purestorage.com> Cc: Kees Cook <keescook@chromium.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Will Deacon <will@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib')
-rw-r--r--lib/Kconfig.debug1
-rw-r--r--lib/Kconfig.kfence67
2 files changed, 68 insertions, 0 deletions
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index f9febffffc21..2779c29d9981 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -938,6 +938,7 @@ config DEBUG_STACKOVERFLOW
If in doubt, say "N".
source "lib/Kconfig.kasan"
+source "lib/Kconfig.kfence"
endmenu # "Memory Debugging"
diff --git a/lib/Kconfig.kfence b/lib/Kconfig.kfence
new file mode 100644
index 000000000000..b88ac9d6b2e6
--- /dev/null
+++ b/lib/Kconfig.kfence
@@ -0,0 +1,67 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+config HAVE_ARCH_KFENCE
+ bool
+
+menuconfig KFENCE
+ bool "KFENCE: low-overhead sampling-based memory safety error detector"
+ depends on HAVE_ARCH_KFENCE && !KASAN && (SLAB || SLUB)
+ select STACKTRACE
+ help
+ KFENCE is a low-overhead sampling-based detector of heap out-of-bounds
+ access, use-after-free, and invalid-free errors. KFENCE is designed
+ to have negligible cost to permit enabling it in production
+ environments.
+
+ Note that, KFENCE is not a substitute for explicit testing with tools
+ such as KASAN. KFENCE can detect a subset of bugs that KASAN can
+ detect, albeit at very different performance profiles. If you can
+ afford to use KASAN, continue using KASAN, for example in test
+ environments. If your kernel targets production use, and cannot
+ enable KASAN due to its cost, consider using KFENCE.
+
+if KFENCE
+
+config KFENCE_STATIC_KEYS
+ bool "Use static keys to set up allocations"
+ default y
+ depends on JUMP_LABEL # To ensure performance, require jump labels
+ help
+ Use static keys (static branches) to set up KFENCE allocations. Using
+ static keys is normally recommended, because it avoids a dynamic
+ branch in the allocator's fast path. However, with very low sample
+ intervals, or on systems that do not support jump labels, a dynamic
+ branch may still be an acceptable performance trade-off.
+
+config KFENCE_SAMPLE_INTERVAL
+ int "Default sample interval in milliseconds"
+ default 100
+ help
+ The KFENCE sample interval determines the frequency with which heap
+ allocations will be guarded by KFENCE. May be overridden via boot
+ parameter "kfence.sample_interval".
+
+ Set this to 0 to disable KFENCE by default, in which case only
+ setting "kfence.sample_interval" to a non-zero value enables KFENCE.
+
+config KFENCE_NUM_OBJECTS
+ int "Number of guarded objects available"
+ range 1 65535
+ default 255
+ help
+ The number of guarded objects available. For each KFENCE object, 2
+ pages are required; with one containing the object and two adjacent
+ ones used as guard pages.
+
+config KFENCE_STRESS_TEST_FAULTS
+ int "Stress testing of fault handling and error reporting" if EXPERT
+ default 0
+ help
+ The inverse probability with which to randomly protect KFENCE object
+ pages, resulting in spurious use-after-frees. The main purpose of
+ this option is to stress test KFENCE with concurrent error reports
+ and allocations/frees. A value of 0 disables stress testing logic.
+
+ Only for KFENCE testing; set to 0 if you are not a KFENCE developer.
+
+endif # KFENCE