Kernel Concurrency Sanitizer (KCSAN) is a dynamic data-race detector for
kernel space. KCSAN is a sampling watchpoint-based data-race detector.
See the included Documentation/dev-tools/kcsan.rst for more details.
This patch adds basic infrastructure, but does not yet enable KCSAN for
any architecture.
Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
---
v2:
* Elaborate comment about instrumentation calls emitted by compilers.
* Replace kcsan_check_access(.., {true, false}) with
kcsan_check_{read,write} for improved readability.
* Change bug title of race of unknown origin to just say "data-race in".
* Refine "Key Properties" in kcsan.rst, and mention observed slow-down.
* Add comment about safety of find_watchpoint without user_access_save.
* Remove unnecessary preempt_disable/enable and elaborate on comment why
we want to disable interrupts and preemptions.
* Use common struct kcsan_ctx in task_struct and for per-CPU interrupt
contexts [Suggested by Mark Rutland].
---
Documentation/dev-tools/kcsan.rst | 203 ++++++++++++++
MAINTAINERS | 11 +
Makefile | 3 +-
include/linux/compiler-clang.h | 9 +
include/linux/compiler-gcc.h | 7 +
include/linux/compiler.h | 35 ++-
include/linux/kcsan-checks.h | 147 ++++++++++
include/linux/kcsan.h | 108 ++++++++
include/linux/sched.h | 4 +
init/init_task.c | 8 +
init/main.c | 2 +
kernel/Makefile | 1 +
kernel/kcsan/Makefile | 14 +
kernel/kcsan/atomic.c | 21 ++
kernel/kcsan/core.c | 428 ++++++++++++++++++++++++++++++
kernel/kcsan/debugfs.c | 225 ++++++++++++++++
kernel/kcsan/encoding.h | 94 +++++++
kernel/kcsan/kcsan.c | 86 ++++++
kernel/kcsan/kcsan.h | 140 ++++++++++
kernel/kcsan/report.c | 306 +++++++++++++++++++++
kernel/kcsan/test.c | 117 ++++++++
lib/Kconfig.debug | 2 +
lib/Kconfig.kcsan | 88 ++++++
lib/Makefile | 3 +
scripts/Makefile.kcsan | 6 +
scripts/Makefile.lib | 10 +
26 files changed, 2069 insertions(+), 9 deletions(-)
create mode 100644 Documentation/dev-tools/kcsan.rst
create mode 100644 include/linux/kcsan-checks.h
create mode 100644 include/linux/kcsan.h
create mode 100644 kernel/kcsan/Makefile
create mode 100644 kernel/kcsan/atomic.c
create mode 100644 kernel/kcsan/core.c
create mode 100644 kernel/kcsan/debugfs.c
create mode 100644 kernel/kcsan/encoding.h
create mode 100644 kernel/kcsan/kcsan.c
create mode 100644 kernel/kcsan/kcsan.h
create mode 100644 kernel/kcsan/report.c
create mode 100644 kernel/kcsan/test.c
create mode 100644 lib/Kconfig.kcsan
create mode 100644 scripts/Makefile.kcsan
diff --git a/Documentation/dev-tools/kcsan.rst b/Documentation/dev-tools/kcsan.rst
new file mode 100644
index 000000000000..497b09e5cc96
--- /dev/null
+++ b/Documentation/dev-tools/kcsan.rst
@@ -0,0 +1,203 @@
+The Kernel Concurrency Sanitizer (KCSAN)
+========================================
+
+Overview
+--------
+
+*Kernel Concurrency Sanitizer (KCSAN)* is a dynamic data-race detector for
+kernel space. KCSAN is a sampling watchpoint-based data-race detector -- this
+is unlike Kernel Thread Sanitizer (KTSAN), which is a happens-before data-race
+detector. Key priorities in KCSAN's design are lack of false positives,
+scalability, and simplicity. More details can be found in `Implementation
+Details`_.
+
+KCSAN uses compile-time instrumentation to instrument memory accesses. KCSAN is
+supported in both GCC and Clang. With GCC it requires version 7.3.0 or later.
+With Clang it requires version 7.0.0 or later.
+
+Usage
+-----
+
+To enable KCSAN configure kernel with::
+
+ CONFIG_KCSAN = y
+
+KCSAN provides several other configuration options to customize behaviour (see
+their respective help text for more info).
+
+debugfs
+~~~~~~~
+
+* The file ``/sys/kernel/debug/kcsan`` can be read to get stats.
+
+* KCSAN can be turned on or off by writing ``on`` or ``off`` to
+ ``/sys/kernel/debug/kcsan``.
+
+* Writing ``!some_func_name`` to ``/sys/kernel/debug/kcsan`` adds
+ ``some_func_name`` to the report filter list, which (by default) blacklists
+ reporting data-races where either one of the top stackframes are a function
+ in the list.
+
+* Writing either ``blacklist`` or ``whitelist`` to ``/sys/kernel/debug/kcsan``
+ changes the report filtering behaviour. For example, the blacklist feature
+ can be used to silence frequently occurring data-races; the whitelist feature
+ can help with reproduction and testing of fixes.
+
+Error reports
+~~~~~~~~~~~~~
+
+A typical data-race report looks like this::
+
+ ==================================================================
+ BUG: KCSAN: data-race in generic_permission / kernfs_refresh_inode
+
+ write to 0xffff8fee4c40700c of 4 bytes by task 175 on cpu 4:
+ kernfs_refresh_inode+0x70/0x170
+ kernfs_iop_permission+0x4f/0x90
+ inode_permission+0x190/0x200
+ link_path_walk.part.0+0x503/0x8e0
+ path_lookupat.isra.0+0x69/0x4d0
+ filename_lookup+0x136/0x280
+ user_path_at_empty+0x47/0x60
+ vfs_statx+0x9b/0x130
+ __do_sys_newlstat+0x50/0xb0
+ __x64_sys_newlstat+0x37/0x50
+ do_syscall_64+0x85/0x260
+ entry_SYSCALL_64_after_hwframe+0x44/0xa9
+
+ read to 0xffff8fee4c40700c of 4 bytes by task 166 on cpu 6:
+ generic_permission+0x5b/0x2a0
+ kernfs_iop_permission+0x66/0x90
+ inode_permission+0x190/0x200
+ link_path_walk.part.0+0x503/0x8e0
+ path_lookupat.isra.0+0x69/0x4d0
+ filename_lookup+0x136/0x280
+ user_path_at_empty+0x47/0x60
+ do_faccessat+0x11a/0x390
+ __x64_sys_access+0x3c/0x50
+ do_syscall_64+0x85/0x260
+ entry_SYSCALL_64_after_hwframe+0x44/0xa9
+
+ Reported by Kernel Concurrency Sanitizer on:
+ CPU: 6 PID: 166 Comm: systemd-journal Not tainted 5.3.0-rc7+ #1
+ Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
+ ==================================================================
+
+The header of the report provides a short summary of the functions involved in
+the race. It is followed by the access types and stack traces of the 2 threads
+involved in the data-race.
+
+The other less common type of data-race report looks like this::
+
+ ==================================================================
+ BUG: KCSAN: data-race in e1000_clean_rx_irq+0x551/0xb10
+
+ race at unknown origin, with read to 0xffff933db8a2ae6c of 1 bytes by interrupt on cpu 0:
+ e1000_clean_rx_irq+0x551/0xb10
+ e1000_clean+0x533/0xda0
+ net_rx_action+0x329/0x900
+ __do_softirq+0xdb/0x2db
+ irq_exit+0x9b/0xa0
+ do_IRQ+0x9c/0xf0
+ ret_from_intr+0x0/0x18
+ default_idle+0x3f/0x220
+ arch_cpu_idle+0x21/0x30
+ do_idle+0x1df/0x230
+ cpu_startup_entry+0x14/0x20
+ rest_init+0xc5/0xcb
+ arch_call_rest_init+0x13/0x2b
+ start_kernel+0x6db/0x700
+
+ Reported by Kernel Concurrency Sanitizer on:
+ CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.3.0-rc7+ #2
+ Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
+ ==================================================================
+
+This report is generated where it was not possible to determine the other
+racing thread, but a race was inferred due to the data-value of the watched
+memory location having changed. These can occur either due to missing
+instrumentation or e.g. DMA accesses.
+
+Data-Races
+----------
+
+Informally, two operations *conflict* if they access the same memory location,
+and at least one of them is a write operation. In an execution, two memory
+operations from different threads form a **data-race** if they *conflict*, at
+least one of them is a *plain access* (non-atomic), and they are *unordered* in
+the "happens-before" order according to the `LKMM
+<../../tools/memory-model/Documentation/explanation.txt>`_.
+
+Relationship with the Linux Kernel Memory Model (LKMM)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The LKMM defines the propagation and ordering rules of various memory
+operations, which gives developers the ability to reason about concurrent code.
+Ultimately this allows to determine the possible executions of concurrent code,
+and if that code is free from data-races.
+
+KCSAN is aware of *atomic* accesses (``READ_ONCE``, ``WRITE_ONCE``,
+``atomic_*``, etc.), but is oblivious of any ordering guarantees. In other
+words, KCSAN assumes that as long as a plain access is not observed to race
+with another conflicting access, memory operations are correctly ordered.
+
+This means that KCSAN will not report *potential* data-races due to missing
+memory ordering. If, however, missing memory ordering (that is observable with
+a particular compiler and architecture) leads to an observable data-race (e.g.
+entering a critical section erroneously), KCSAN would report the resulting
+data-race.
+
+Implementation Details
+----------------------
+
+The general approach is inspired by `DataCollider
+<http://usenix.org/legacy/events/osdi10/tech/full_papers/Erickson.pdf>`_.
+Unlike DataCollider, KCSAN does not use hardware watchpoints, but instead
+relies on compiler instrumentation. Watchpoints are implemented using an
+efficient encoding that stores access type, size, and address in a long; the
+benefits of using "soft watchpoints" are portability and greater flexibility in
+limiting which accesses trigger a watchpoint.
+
+More specifically, KCSAN requires instrumenting plain (unmarked, non-atomic)
+memory operations; for each instrumented plain access:
+
+1. Check if a matching watchpoint exists; if yes, and at least one access is a
+ write, then we encountered a racing access.
+
+2. Periodically, if no matching watchpoint exists, set up a watchpoint and
+ stall some delay.
+
+3. Also check the data value before the delay, and re-check the data value
+ after delay; if the values mismatch, we infer a race of unknown origin.
+
+To detect data-races between plain and atomic memory operations, KCSAN also
+annotates atomic accesses, but only to check if a watchpoint exists
+(``kcsan_check_atomic_*``); i.e. KCSAN never sets up a watchpoint on atomic
+accesses.
+
+Key Properties
+~~~~~~~~~~~~~~
+
+1. **Memory Overhead:** No shadow memory is required. The current
+ implementation uses a small array of longs to encode watchpoint information,
+ which is negligible.
+
+2. **Performance Overhead:** KCSAN's runtime aims to be minimal, using an
+ efficient watchpoint encoding that does not require acquiring any shared
+ locks in the fast-path. For kernel boot with a default config on a system
+ where nproc=8 we measure a slow-down of 10-15x.
+
+3. **Memory Ordering:** KCSAN is *not* aware of the LKMM's ordering rules. This
+ may result in missed data-races (false negatives), compared to a
+ happens-before data-race detector.
+
+4. **Accuracy:** Imprecise, since it uses a sampling strategy.
+
+5. **Annotation Overheads:** Minimal annotation is required outside the KCSAN
+ runtime. With a happens-before data-race detector, any omission leads to
+ false positives, which is especially important in the context of the kernel
+ which includes numerous custom synchronization mechanisms. With KCSAN, as a
+ result, maintenance overheads are minimal as the kernel evolves.
+
+6. **Detects Racy Writes from Devices:** Due to checking data values upon
+ setting up watchpoints, racy writes from devices can also be detected.
diff --git a/MAINTAINERS b/MAINTAINERS
index 0154674cbad3..71f7fb625490 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8847,6 +8847,17 @@ F: Documentation/kbuild/kconfig*
F: scripts/kconfig/
F: scripts/Kconfig.include
+KCSAN
+M: Marco Elver <elver@xxxxxxxxxx>
+R: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
+L: kasan-dev@xxxxxxxxxxxxxxxx
+S: Maintained
+F: Documentation/dev-tools/kcsan.rst
+F: include/linux/kcsan*.h
+F: kernel/kcsan/
+F: lib/Kconfig.kcsan
+F: scripts/Makefile.kcsan
+
KDUMP
M: Dave Young <dyoung@xxxxxxxxxx>
M: Baoquan He <bhe@xxxxxxxxxx>
diff --git a/Makefile b/Makefile
index ffd7a912fc46..ad4729176252 100644
--- a/Makefile
+++ b/Makefile
@@ -478,7 +478,7 @@ export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS LDFLAGS_MODULE
export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS
export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
-export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN
+export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN CFLAGS_KCSAN
export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE
export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
@@ -900,6 +900,7 @@ endif
include scripts/Makefile.kasan
include scripts/Makefile.extrawarn
include scripts/Makefile.ubsan
+include scripts/Makefile.kcsan
# Add user supplied CPPFLAGS, AFLAGS and CFLAGS as the last assignments
KBUILD_CPPFLAGS += $(KCPPFLAGS)
diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index 333a6695a918..a213eb55e725 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -24,6 +24,15 @@
#define __no_sanitize_address
#endif
+#if __has_feature(thread_sanitizer)
+/* emulate gcc's __SANITIZE_THREAD__ flag */
+#define __SANITIZE_THREAD__
+#define __no_sanitize_thread \
+ __attribute__((no_sanitize("thread")))
+#else
+#define __no_sanitize_thread
+#endif
+
/*
* Not all versions of clang implement the the type-generic versions
* of the builtin overflow checkers. Fortunately, clang implements
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index d7ee4c6bad48..de105ca29282 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -145,6 +145,13 @@
#define __no_sanitize_address
#endif
+#if __has_attribute(__no_sanitize_thread__) && defined(__SANITIZE_THREAD__)
+#define __no_sanitize_thread \
+ __attribute__((__noinline__)) __attribute__((no_sanitize_thread))
+#else
+#define __no_sanitize_thread
+#endif
+
#if GCC_VERSION >= 50100
#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
#endif
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 5e88e7e33abe..350d80dbee4d 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -178,6 +178,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
#endif
#include <uapi/linux/types.h>
+#include <linux/kcsan-checks.h>
#define __READ_ONCE_SIZE \
({ \
@@ -193,12 +194,6 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
} \
})
-static __always_inline
-void __read_once_size(const volatile void *p, void *res, int size)
-{
- __READ_ONCE_SIZE;
-}
-
#ifdef CONFIG_KASAN
/*
* We can't declare function 'inline' because __no_sanitize_address confilcts
@@ -211,14 +206,38 @@ void __read_once_size(const volatile void *p, void *res, int size)
# define __no_kasan_or_inline __always_inline
#endif
-static __no_kasan_or_inline
+#ifdef CONFIG_KCSAN
+# define __no_kcsan_or_inline __no_sanitize_thread notrace __maybe_unused
+#else
+# define __no_kcsan_or_inline __always_inline
+#endif
+
+#if defined(CONFIG_KASAN) || defined(CONFIG_KCSAN)
+/* Avoid any instrumentation or inline. */
+#define __no_sanitize_or_inline \
+ __no_sanitize_address __no_sanitize_thread notrace __maybe_unused
+#else
+#define __no_sanitize_or_inline __always_inline
+#endif
+
+static __no_kcsan_or_inline
+void __read_once_size(const volatile void *p, void *res, int size)
+{
+ kcsan_check_atomic_read((const void *)p, size);
+ __READ_ONCE_SIZE;
+}
+
+static __no_sanitize_or_inline
void __read_once_size_nocheck(const volatile void *p, void *res, int size)
{
__READ_ONCE_SIZE;
}
-static __always_inline void __write_once_size(volatile void *p, void *res, int size)
+static __no_kcsan_or_inline
+void __write_once_size(volatile void *p, void *res, int size)
{
+ kcsan_check_atomic_write((const void *)p, size);
+
switch (size) {
case 1: *(volatile __u8 *)p = *(__u8 *)res; break;
case 2: *(volatile __u16 *)p = *(__u16 *)res; break;
diff --git a/include/linux/kcsan-checks.h b/include/linux/kcsan-checks.h
new file mode 100644
index 000000000000..4203603ae852
--- /dev/null
+++ b/include/linux/kcsan-checks.h
@@ -0,0 +1,147 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_KCSAN_CHECKS_H
+#define _LINUX_KCSAN_CHECKS_H
+
+#include <linux/types.h>
+
+/*
+ * __kcsan_*: Always available when KCSAN is enabled. This may be used
+ * even in compilation units that selectively disable KCSAN, but must use KCSAN
+ * to validate access to an address. Never use these in header files!
+ */
+#ifdef CONFIG_KCSAN
+/**
+ * __kcsan_check_watchpoint - check if a watchpoint exists
+ *
+ * Returns true if no race was detected, and we may then proceed to set up a
+ * watchpoint after. Returns false if either KCSAN is disabled or a race was
+ * encountered, and we may not set up a watchpoint after.
+ *
+ * @ptr address of access
+ * @size size of access
+ * @is_write is access a write
+ * @return true if no race was detected, false otherwise.
+ */
+bool __kcsan_check_watchpoint(const volatile void *ptr, size_t size,
+ bool is_write);
+
+/**
+ * __kcsan_setup_watchpoint - set up watchpoint and report data-races
+ *
+ * Sets up a watchpoint (if sampled), and if a racing access was observed,
+ * reports the data-race.
+ *
+ * @ptr address of access
+ * @size size of access
+ * @is_write is access a write
+ */
+void __kcsan_setup_watchpoint(const volatile void *ptr, size_t size,
+ bool is_write);
+#else
+static inline bool __kcsan_check_watchpoint(const volatile void *ptr,
+ size_t size, bool is_write)
+{
+ return true;
+}
+static inline void __kcsan_setup_watchpoint(const volatile void *ptr,
+ size_t size, bool is_write)
+{
+}
+#endif
+
+/*
+ * kcsan_*: Only available when the particular compilation unit has KCSAN
+ * instrumentation enabled. May be used in header files.
+ */
+#ifdef __SANITIZE_THREAD__
+#define kcsan_check_watchpoint __kcsan_check_watchpoint
+#define kcsan_setup_watchpoint __kcsan_setup_watchpoint
+#else
+static inline bool kcsan_check_watchpoint(const volatile void *ptr, size_t size,
+ bool is_write)
+{
+ return true;
+}
+static inline void kcsan_setup_watchpoint(const volatile void *ptr, size_t size,
+ bool is_write)
+{
+}
+#endif
+
+/**
+ * __kcsan_check_read - check regular read access for data-races
+ *
+ * Full read access that checks watchpoint and sets up a watchpoint if this
+ * access is sampled. Note that, setting up watchpoints for plain reads is
+ * required to also detect data-races with atomic accesses.
+ *
+ * @ptr address of access
+ * @size size of access
+ */
+#define __kcsan_check_read(ptr, size) \
+ do { \
+ if (__kcsan_check_watchpoint(ptr, size, false)) \
+ __kcsan_setup_watchpoint(ptr, size, false); \
+ } while (0)
+
+/**
+ * __kcsan_check_write - check regular write access for data-races
+ *
+ * Full write access that checks watchpoint and sets up a watchpoint if this
+ * access is sampled.
+ *
+ * @ptr address of access
+ * @size size of access
+ */
+#define __kcsan_check_write(ptr, size) \
+ do { \
+ if (__kcsan_check_watchpoint(ptr, size, true) && \
+ !IS_ENABLED(CONFIG_KCSAN_PLAIN_WRITE_PRETEND_ONCE)) \
+ __kcsan_setup_watchpoint(ptr, size, true); \
+ } while (0)
+
+/**
+ * kcsan_check_read - check regular read access for data-races
+ *
+ * @ptr address of access
+ * @size size of access
+ */
+#define kcsan_check_read(ptr, size) \
+ do { \
+ if (kcsan_check_watchpoint(ptr, size, false)) \
+ kcsan_setup_watchpoint(ptr, size, false); \
+ } while (0)
+
+/**
+ * kcsan_check_write - check regular write access for data-races
+ *
+ * @ptr address of access
+ * @size size of access
+ */
+#define kcsan_check_write(ptr, size) \
+ do { \
+ if (kcsan_check_watchpoint(ptr, size, true) && \
+ !IS_ENABLED(CONFIG_KCSAN_PLAIN_WRITE_PRETEND_ONCE)) \
+ kcsan_setup_watchpoint(ptr, size, true); \
+ } while (0)
+
+/*
+ * Check for atomic accesses: if atomic access are not ignored, this simply
+ * aliases to kcsan_check_watchpoint, otherwise becomes a no-op.
+ */
+#ifdef CONFIG_KCSAN_IGNORE_ATOMICS
+#define kcsan_check_atomic_read(...) \
+ do { \
+ } while (0)
+#define kcsan_check_atomic_write(...) \
+ do { \
+ } while (0)
+#else
+#define kcsan_check_atomic_read(ptr, size) \
+ kcsan_check_watchpoint(ptr, size, false)
+#define kcsan_check_atomic_write(ptr, size) \
+ kcsan_check_watchpoint(ptr, size, true)
+#endif
+
+#endif /* _LINUX_KCSAN_CHECKS_H */
diff --git a/include/linux/kcsan.h b/include/linux/kcsan.h
new file mode 100644
index 000000000000..fd5de2ba3a16
--- /dev/null
+++ b/include/linux/kcsan.h
@@ -0,0 +1,108 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_KCSAN_H
+#define _LINUX_KCSAN_H
+
+#include <linux/types.h>
+#include <linux/kcsan-checks.h>
+
+#ifdef CONFIG_KCSAN
+
+/*
+ * Context for each thread of execution: for tasks, this is stored in
+ * task_struct, and interrupts access internal per-CPU storage.
+ */
+struct kcsan_ctx {
+ int disable; /* disable counter */
+ int atomic_next; /* number of following atomic ops */
+
+ /*
+ * We use separate variables to store if we are in a nestable or flat
+ * atomic region. This helps make sure that an atomic region with
+ * nesting support is not suddenly aborted when a flat region is
+ * contained within. Effectively this allows supporting nesting flat
+ * atomic regions within an outer nestable atomic region. Support for
+ * this is required as there are cases where a seqlock reader critical
+ * section (flat atomic region) is contained within a seqlock writer
+ * critical section (nestable atomic region), and the "mismatching
+ * kcsan_end_atomic()" warning would trigger otherwise.
+ */
+ int atomic_region;
+ bool atomic_region_flat;
+};
+
+/**
+ * kcsan_init - initialize KCSAN runtime
+ */
+void kcsan_init(void);
+
+/**
+ * kcsan_disable_current - disable KCSAN for the current context
+ *
+ * Supports nesting.
+ */
+void kcsan_disable_current(void);
+
+/**
+ * kcsan_enable_current - re-enable KCSAN for the current context
+ *
+ * Supports nesting.
+ */
+void kcsan_enable_current(void);
+
+/**
+ * kcsan_begin_atomic - use to denote an atomic region
+ *
+ * Accesses within the atomic region may appear to race with other accesses but
+ * should be considered atomic.
+ *
+ * @nest true if regions may be nested, or false for flat region
+ */
+void kcsan_begin_atomic(bool nest);
+
+/**
+ * kcsan_end_atomic - end atomic region
+ *
+ * @nest must match argument to kcsan_begin_atomic().
+ */
+void kcsan_end_atomic(bool nest);
+
+/**
+ * kcsan_atomic_next - consider following accesses as atomic
+ *
+ * Force treating the next n memory accesses for the current context as atomic
+ * operations.
+ *
+ * @n number of following memory accesses to treat as atomic.
+ */
+void kcsan_atomic_next(int n);
+
+#else /* CONFIG_KCSAN */
+
+static inline void kcsan_init(void)
+{
+}
+
+static inline void kcsan_disable_current(void)
+{
+}
+
+static inline void kcsan_enable_current(void)
+{
+}
+
+static inline void kcsan_begin_atomic(bool nest)
+{
+}
+
+static inline void kcsan_end_atomic(bool nest)
+{
+}
+
+static inline void kcsan_atomic_next(int n)
+{
+}
+
+#endif /* CONFIG_KCSAN */
+
+#endif /* _LINUX_KCSAN_H */
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2c2e56bd8913..9490e417bf4a 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -31,6 +31,7 @@
#include <linux/task_io_accounting.h>
#include <linux/posix-timers.h>
#include <linux/rseq.h>
+#include <linux/kcsan.h>
/* task_struct member predeclarations (sorted alphabetically): */
struct audit_context;
@@ -1171,6 +1172,9 @@ struct task_struct {
#ifdef CONFIG_KASAN
unsigned int kasan_depth;
#endif
+#ifdef CONFIG_KCSAN
+ struct kcsan_ctx kcsan_ctx;
+#endif
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
/* Index of current stored address in ret_stack: */
diff --git a/init/init_task.c b/init/init_task.c
index 9e5cbe5eab7b..e229416c3314 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -161,6 +161,14 @@ struct task_struct init_task
#ifdef CONFIG_KASAN
.kasan_depth = 1,
#endif
+#ifdef CONFIG_KCSAN
+ .kcsan_ctx = {
+ .disable = 1,
+ .atomic_next = 0,
+ .atomic_region = 0,
+ .atomic_region_flat = 0,
+ },
+#endif
#ifdef CONFIG_TRACE_IRQFLAGS
.softirqs_enabled = 1,
#endif
diff --git a/init/main.c b/init/main.c
index 91f6ebb30ef0..4d814de017ee 100644
--- a/init/main.c
+++ b/init/main.c
@@ -93,6 +93,7 @@
#include <linux/rodata_test.h>
#include <linux/jump_label.h>
#include <linux/mem_encrypt.h>
+#include <linux/kcsan.h>
#include <asm/io.h>
#include <asm/bugs.h>
@@ -779,6 +780,7 @@ asmlinkage __visible void __init start_kernel(void)
acpi_subsystem_init();
arch_post_acpi_subsys_init();
sfi_init_late();
+ kcsan_init();
/* Do the rest non-__init'ed, we're now alive */
arch_call_rest_init();
diff --git a/kernel/Makefile b/kernel/Makefile
index daad787fb795..74ab46e2ebd1 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -102,6 +102,7 @@ obj-$(CONFIG_TRACEPOINTS) += trace/
obj-$(CONFIG_IRQ_WORK) += irq_work.o
obj-$(CONFIG_CPU_PM) += cpu_pm.o
obj-$(CONFIG_BPF) += bpf/
+obj-$(CONFIG_KCSAN) += kcsan/
obj-$(CONFIG_PERF_EVENTS) += events/
diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
new file mode 100644
index 000000000000..c25f07062d26
--- /dev/null
+++ b/kernel/kcsan/Makefile
@@ -0,0 +1,14 @@
+# SPDX-License-Identifier: GPL-2.0
+KCSAN_SANITIZE := n
+KCOV_INSTRUMENT := n
+
+CFLAGS_REMOVE_kcsan.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE)
+CFLAGS_REMOVE_atomic.o = $(CC_FLAGS_FTRACE)
+
+CFLAGS_kcsan.o = $(call cc-option, -fno-conserve-stack -fno-stack-protector)
+CFLAGS_core.o = $(call cc-option, -fno-conserve-stack -fno-stack-protector)
+CFLAGS_atomic.o = $(call cc-option, -fno-conserve-stack -fno-stack-protector)
+
+obj-y := kcsan.o core.o atomic.o debugfs.o report.o
+obj-$(CONFIG_KCSAN_SELFTEST) += test.o
diff --git a/kernel/kcsan/atomic.c b/kernel/kcsan/atomic.c
new file mode 100644
index 000000000000..dd44f7d9e491
--- /dev/null
+++ b/kernel/kcsan/atomic.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/jiffies.h>
+
+#include "kcsan.h"
+
+/*
+ * List all volatile globals that have been observed in races, to suppress
+ * data-race reports between accesses to these variables.
+ *
+ * For now, we assume that volatile accesses of globals are as strong as atomic
+ * accesses (READ_ONCE, WRITE_ONCE cast to volatile). The situation is still not
+ * entirely clear, as on some architectures (Alpha) READ_ONCE/WRITE_ONCE do more
+ * than cast to volatile. Eventually, we hope to be able to remove this
+ * function.
+ */
+bool kcsan_is_atomic(const volatile void *ptr)
+{
+ /* only jiffies for now */
+ return ptr == &jiffies;
+}
diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
new file mode 100644
index 000000000000..bc8d60b129eb
--- /dev/null
+++ b/kernel/kcsan/core.c
@@ -0,0 +1,428 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/atomic.h>
+#include <linux/bug.h>
+#include <linux/delay.h>
+#include <linux/export.h>
+#include <linux/init.h>
+#include <linux/percpu.h>
+#include <linux/preempt.h>
+#include <linux/random.h>
+#include <linux/sched.h>
+#include <linux/uaccess.h>
+
+#include "kcsan.h"
+#include "encoding.h"
+
+/*
+ * Helper macros to iterate slots, starting from address slot itself, followed
+ * by the right and left slots.
+ */
+#define CHECK_NUM_SLOTS (1 + 2 * KCSAN_CHECK_ADJACENT)
+#define SLOT_IDX(slot, i) \
+ ((slot + (((i + KCSAN_CHECK_ADJACENT) % CHECK_NUM_SLOTS) - \
+ KCSAN_CHECK_ADJACENT)) % \
+ KCSAN_NUM_WATCHPOINTS)
+
+bool kcsan_enabled;
+
+/* Per-CPU kcsan_ctx for interrupts */
+static DEFINE_PER_CPU(struct kcsan_ctx, kcsan_cpu_ctx) = {
+ .disable = 0,
+ .atomic_next = 0,
+ .atomic_region = 0,
+ .atomic_region_flat = 0,
+};
+
+/*
+ * Watchpoints, with each entry encoded as defined in encoding.h: in order to be
+ * able to safely update and access a watchpoint without introducing locking
+ * overhead, we encode each watchpoint as a single atomic long. The initial
+ * zero-initialized state matches INVALID_WATCHPOINT.
+ */
+static atomic_long_t watchpoints[KCSAN_NUM_WATCHPOINTS];
+
+/*
+ * Instructions skipped counter; see should_watch().
+ */
+static DEFINE_PER_CPU(unsigned long, kcsan_skip);
+
+static inline atomic_long_t *find_watchpoint(unsigned long addr, size_t size,
+ bool expect_write,
+ long *encoded_watchpoint)
+{
+ const int slot = watchpoint_slot(addr);
+ const unsigned long addr_masked = addr & WATCHPOINT_ADDR_MASK;
+ atomic_long_t *watchpoint;
+ unsigned long wp_addr_masked;
+ size_t wp_size;
+ bool is_write;
+ int i;
+
+ for (i = 0; i < CHECK_NUM_SLOTS; ++i) {
+ watchpoint = &watchpoints[SLOT_IDX(slot, i)];
+ *encoded_watchpoint = atomic_long_read(watchpoint);
+ if (!decode_watchpoint(*encoded_watchpoint, &wp_addr_masked,
+ &wp_size, &is_write))
+ continue;
+
+ if (expect_write && !is_write)
+ continue;
+
+ /* Check if the watchpoint matches the access. */
+ if (matching_access(wp_addr_masked, wp_size, addr_masked, size))
+ return watchpoint;
+ }
+
+ return NULL;
+}
+
+static inline atomic_long_t *insert_watchpoint(unsigned long addr, size_t size,
+ bool is_write)
+{
+ const int slot = watchpoint_slot(addr);
+ const long encoded_watchpoint = encode_watchpoint(addr, size, is_write);
+ atomic_long_t *watchpoint;
+ int i;
+
+ for (i = 0; i < CHECK_NUM_SLOTS; ++i) {
+ long expect_val = INVALID_WATCHPOINT;
+
+ /* Try to acquire this slot. */
+ watchpoint = &watchpoints[SLOT_IDX(slot, i)];
+ if (atomic_long_try_cmpxchg_relaxed(watchpoint, &expect_val,
+ encoded_watchpoint))
+ return watchpoint;
+ }
+
+ return NULL;
+}
+
+/*
+ * Return true if watchpoint was successfully consumed, false otherwise.
+ *
+ * This may return false if:
+ *
+ * 1. another thread already consumed the watchpoint;
+ * 2. the thread that set up the watchpoint already removed it;
+ * 3. the watchpoint was removed and then re-used.
+ */
+static inline bool try_consume_watchpoint(atomic_long_t *watchpoint,
+ long encoded_watchpoint)
+{
+ return atomic_long_try_cmpxchg_relaxed(watchpoint, &encoded_watchpoint,
+ CONSUMED_WATCHPOINT);
+}
+
+/*
+ * Return true if watchpoint was not touched, false if consumed.
+ */
+static inline bool remove_watchpoint(atomic_long_t *watchpoint)
+{
+ return atomic_long_xchg_relaxed(watchpoint, INVALID_WATCHPOINT) !=
+ CONSUMED_WATCHPOINT;
+}
+
+static inline struct kcsan_ctx *get_ctx(void)
+{
+ /*
+ * In interrupt, use raw_cpu_ptr to avoid unnecessary checks, that would
+ * also result in calls that generate warnings in uaccess regions.
+ */
+ return in_task() ? ¤t->kcsan_ctx : raw_cpu_ptr(&kcsan_cpu_ctx);
+}
+
+static inline bool is_atomic(const volatile void *ptr)
+{
+ struct kcsan_ctx *ctx = get_ctx();
+
+ if (unlikely(ctx->atomic_next > 0)) {
+ --ctx->atomic_next;
+ return true;
+ }
+ if (unlikely(ctx->atomic_region > 0 || ctx->atomic_region_flat))
+ return true;
+
+ return kcsan_is_atomic(ptr);
+}
+
+static inline bool should_watch(const volatile void *ptr)
+{
+ /*
+ * Never set up watchpoints when memory operations are atomic.
+ *
+ * We need to check this first, because: 1) atomics should not count
+ * towards skipped instructions below, and 2) to actually decrement
+ * kcsan_atomic_next for each atomic.
+ */
+ if (is_atomic(ptr))
+ return false;
+
+ /*
+ * We use a per-CPU counter, to avoid excessive contention; there is
+ * still enough non-determinism for the precise instructions that end up
+ * being watched to be mostly unpredictable. Using a PRNG like
+ * prandom_u32() turned out to be too slow.
+ */
+ return (this_cpu_inc_return(kcsan_skip) %
+ CONFIG_KCSAN_WATCH_SKIP_INST) == 0;
+}
+
+static inline bool is_enabled(void)
+{
+ return READ_ONCE(kcsan_enabled) && get_ctx()->disable == 0;
+}
+
+static inline unsigned int get_delay(void)
+{
+ unsigned int max_delay = in_task() ? CONFIG_KCSAN_UDELAY_MAX_TASK :
+ CONFIG_KCSAN_UDELAY_MAX_INTERRUPT;
+ return IS_ENABLED(CONFIG_KCSAN_DELAY_RANDOMIZE) ?
+ ((prandom_u32() % max_delay) + 1) :
+ max_delay;
+}
+
+/* === Public interface ===================================================== */
+
+void __init kcsan_init(void)
+{
+ BUG_ON(!in_task());
+
+ kcsan_debugfs_init();
+ kcsan_enable_current();
+#ifdef CONFIG_KCSAN_EARLY_ENABLE
+ /*
+ * We are in the init task, and no other tasks should be running.
+ */
+ WRITE_ONCE(kcsan_enabled, true);
+#endif
+}
+
+/* === Exported interface =================================================== */
+
+void kcsan_disable_current(void)
+{
+ ++get_ctx()->disable;
+}
+EXPORT_SYMBOL(kcsan_disable_current);
+
+void kcsan_enable_current(void)
+{
+ if (get_ctx()->disable-- == 0) {
+ kcsan_disable_current(); /* restore to 0 */
+ kcsan_disable_current();
+ WARN(1, "mismatching %s", __func__);
+ kcsan_enable_current();
+ }
+}
+EXPORT_SYMBOL(kcsan_enable_current);
+
+void kcsan_begin_atomic(bool nest)
+{
+ if (nest)
+ ++get_ctx()->atomic_region;
+ else
+ get_ctx()->atomic_region_flat = true;
+}
+EXPORT_SYMBOL(kcsan_begin_atomic);
+
+void kcsan_end_atomic(bool nest)
+{
+ if (nest) {
+ if (get_ctx()->atomic_region-- == 0) {
+ kcsan_begin_atomic(true); /* restore to 0 */
+ kcsan_disable_current();
+ WARN(1, "mismatching %s", __func__);
+ kcsan_enable_current();
+ }
+ } else {
+ get_ctx()->atomic_region_flat = false;
+ }
+}
+EXPORT_SYMBOL(kcsan_end_atomic);
+
+void kcsan_atomic_next(int n)
+{
+ get_ctx()->atomic_next = n;
+}
+EXPORT_SYMBOL(kcsan_atomic_next);
+
+bool __kcsan_check_watchpoint(const volatile void *ptr, size_t size,
+ bool is_write)
+{
+ atomic_long_t *watchpoint;
+ long encoded_watchpoint;
+ unsigned long flags;
+ enum kcsan_report_type report_type;
+
+ if (unlikely(!is_enabled()))
+ return false;
+
+ /*
+ * Avoid user_access_save in fast-path here: find_watchpoint is safe
+ * without user_access_save, as the address that ptr points to is only
+ * used to check if a watchpoint exists; ptr is never dereferenced.
+ */
+ watchpoint = find_watchpoint((unsigned long)ptr, size, !is_write,
+ &encoded_watchpoint);
+ if (watchpoint == NULL)
+ return true;
+
+ flags = user_access_save();
+ if (!try_consume_watchpoint(watchpoint, encoded_watchpoint)) {
+ /*
+ * The other thread may not print any diagnostics, as it has
+ * already removed the watchpoint, or another thread consumed
+ * the watchpoint before this thread.
+ */
+ kcsan_counter_inc(kcsan_counter_report_races);
+ report_type = kcsan_report_race_check_race;
+ } else {
+ report_type = kcsan_report_race_check;
+ }
+
+ /* Encountered a data-race. */
+ kcsan_counter_inc(kcsan_counter_data_races);
+ kcsan_report(ptr, size, is_write, raw_smp_processor_id(), report_type);
+
+ user_access_restore(flags);
+ return false;
+}
+EXPORT_SYMBOL(__kcsan_check_watchpoint);
+
+void __kcsan_setup_watchpoint(const volatile void *ptr, size_t size,
+ bool is_write)
+{
+ atomic_long_t *watchpoint;
+ union {
+ u8 _1;
+ u16 _2;
+ u32 _4;
+ u64 _8;
+ } expect_value;
+ bool is_expected = true;
+ unsigned long ua_flags = user_access_save();
+ unsigned long irq_flags;
+
+ if (!should_watch(ptr))
+ goto out;
+
+ if (!check_encodable((unsigned long)ptr, size)) {
+ kcsan_counter_inc(kcsan_counter_unencodable_accesses);
+ goto out;
+ }
+
+ /*
+ * Disable interrupts & preemptions to avoid another thread on the same
+ * CPU accessing memory locations for the set up watchpoint; this is to
+ * avoid reporting races to e.g. CPU-local data.
+ *
+ * An alternative would be adding the source CPU to the watchpoint
+ * encoding, and checking that watchpoint-CPU != this-CPU. There are
+ * several problems with this:
+ * 1. we should avoid stealing more bits from the watchpoint encoding
+ * as it would affect accuracy, as well as increase performance
+ * overhead in the fast-path;
+ * 2. if we are preempted, but there *is* a genuine data-race, we
+ * would *not* report it -- since this is the common case (vs.
+ * CPU-local data accesses), it makes more sense (from a data-race
+ * detection PoV) to simply disable preemptions to ensure as many
+ * tasks as possible run on other CPUs.
+ */
+ local_irq_save(irq_flags);
+
+ watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write);
+ if (watchpoint == NULL) {
+ /*
+ * Out of capacity: the size of `watchpoints`, and the frequency
+ * with which `should_watch()` returns true should be tweaked so
+ * that this case happens very rarely.
+ */
+ kcsan_counter_inc(kcsan_counter_no_capacity);
+ goto out_unlock;
+ }
+
+ kcsan_counter_inc(kcsan_counter_setup_watchpoints);
+ kcsan_counter_inc(kcsan_counter_used_watchpoints);
+
+ /*
+ * Read the current value, to later check and infer a race if the data
+ * was modified via a non-instrumented access, e.g. from a device.
+ */
+ switch (size) {
+ case 1:
+ expect_value._1 = READ_ONCE(*(const u8 *)ptr);
+ break;
+ case 2:
+ expect_value._2 = READ_ONCE(*(const u16 *)ptr);
+ break;
+ case 4:
+ expect_value._4 = READ_ONCE(*(const u32 *)ptr);
+ break;
+ case 8:
+ expect_value._8 = READ_ONCE(*(const u64 *)ptr);
+ break;
+ default:
+ break; /* ignore; we do not diff the values */
+ }
+
+#ifdef CONFIG_KCSAN_DEBUG
+ kcsan_disable_current();
+ pr_err("KCSAN: watching %s, size: %zu, addr: %px [slot: %d, encoded: %lx]\n",
+ is_write ? "write" : "read", size, ptr,
+ watchpoint_slot((unsigned long)ptr),
+ encode_watchpoint((unsigned long)ptr, size, is_write));
+ kcsan_enable_current();
+#endif
+
+ /*
+ * Delay this thread, to increase probability of observing a racy
+ * conflicting access.
+ */
+ udelay(get_delay());
+
+ /*
+ * Re-read value, and check if it is as expected; if not, we infer a
+ * racy access.
+ */
+ switch (size) {
+ case 1:
+ is_expected = expect_value._1 == READ_ONCE(*(const u8 *)ptr);
+ break;
+ case 2:
+ is_expected = expect_value._2 == READ_ONCE(*(const u16 *)ptr);
+ break;
+ case 4:
+ is_expected = expect_value._4 == READ_ONCE(*(const u32 *)ptr);
+ break;
+ case 8:
+ is_expected = expect_value._8 == READ_ONCE(*(const u64 *)ptr);
+ break;
+ default:
+ break; /* ignore; we do not diff the values */
+ }
+
+ /* Check if this access raced with another. */
+ if (!remove_watchpoint(watchpoint)) {
+ /*
+ * No need to increment 'race' counter, as the racing thread
+ * already did.
+ */
+ kcsan_report(ptr, size, is_write, smp_processor_id(),
+ kcsan_report_race_setup);
+ } else if (!is_expected) {
+ /* Inferring a race, since the value should not have changed. */
+ kcsan_counter_inc(kcsan_counter_races_unknown_origin);
+#ifdef CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
+ kcsan_report(ptr, size, is_write, smp_processor_id(),
+ kcsan_report_race_unknown_origin);
+#endif
+ }
+
+ kcsan_counter_dec(kcsan_counter_used_watchpoints);
+out_unlock:
+ local_irq_restore(irq_flags);
+out:
+ user_access_restore(ua_flags);
+}
+EXPORT_SYMBOL(__kcsan_setup_watchpoint);
diff --git a/kernel/kcsan/debugfs.c b/kernel/kcsan/debugfs.c
new file mode 100644
index 000000000000..6ddcbd185f3a
--- /dev/null
+++ b/kernel/kcsan/debugfs.c
@@ -0,0 +1,225 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/atomic.h>
+#include <linux/bsearch.h>
+#include <linux/bug.h>
+#include <linux/debugfs.h>
+#include <linux/init.h>
+#include <linux/kallsyms.h>
+#include <linux/mm.h>
+#include <linux/seq_file.h>
+#include <linux/sort.h>
+#include <linux/string.h>
+#include <linux/uaccess.h>
+
+#include "kcsan.h"
+
+/*
+ * Statistics counters.
+ */
+static atomic_long_t counters[kcsan_counter_count];
+
+/*
+ * Addresses for filtering functions from reporting. This list can be used as a
+ * whitelist or blacklist.
+ */
+static struct {
+ unsigned long *addrs; /* array of addresses */
+ size_t size; /* current size */
+ int used; /* number of elements used */
+ bool sorted; /* if elements are sorted */
+ bool whitelist; /* if list is a blacklist or whitelist */
+} report_filterlist = {
+ .addrs = NULL,
+ .size = 8, /* small initial size */
+ .used = 0,
+ .sorted = false,
+ .whitelist = false, /* default is blacklist */
+};
+static DEFINE_SPINLOCK(report_filterlist_lock);
+
+static const char *counter_to_name(enum kcsan_counter_id id)
+{
+ switch (id) {
+ case kcsan_counter_used_watchpoints:
+ return "used_watchpoints";
+ case kcsan_counter_setup_watchpoints:
+ return "setup_watchpoints";
+ case kcsan_counter_data_races:
+ return "data_races";
+ case kcsan_counter_no_capacity:
+ return "no_capacity";
+ case kcsan_counter_report_races:
+ return "report_races";
+ case kcsan_counter_races_unknown_origin:
+ return "races_unknown_origin";
+ case kcsan_counter_unencodable_accesses:
+ return "unencodable_accesses";
+ case kcsan_counter_encoding_false_positives:
+ return "encoding_false_positives";
+ case kcsan_counter_count:
+ BUG();
+ }
+ return NULL;
+}
+
+void kcsan_counter_inc(enum kcsan_counter_id id)
+{
+ atomic_long_inc(&counters[id]);
+}
+
+void kcsan_counter_dec(enum kcsan_counter_id id)
+{
+ atomic_long_dec(&counters[id]);
+}
+
+static int cmp_filterlist_addrs(const void *rhs, const void *lhs)
+{
+ const unsigned long a = *(const unsigned long *)rhs;
+ const unsigned long b = *(const unsigned long *)lhs;
+
+ return a < b ? -1 : a == b ? 0 : 1;
+}
+
+bool kcsan_skip_report(unsigned long func_addr)
+{
+ unsigned long symbolsize, offset;
+ unsigned long flags;
+ bool ret = false;
+
+ if (!kallsyms_lookup_size_offset(func_addr, &symbolsize, &offset))
+ return false;
+ func_addr -= offset; /* get function start */
+
+ spin_lock_irqsave(&report_filterlist_lock, flags);
+ if (report_filterlist.used == 0)
+ goto out;
+
+ /* Sort array if it is unsorted, and then do a binary search. */
+ if (!report_filterlist.sorted) {
+ sort(report_filterlist.addrs, report_filterlist.used,
+ sizeof(unsigned long), cmp_filterlist_addrs, NULL);
+ report_filterlist.sorted = true;
+ }
+ ret = !!bsearch(&func_addr, report_filterlist.addrs,
+ report_filterlist.used, sizeof(unsigned long),
+ cmp_filterlist_addrs);
+ if (report_filterlist.whitelist)
+ ret = !ret;
+
+out:
+ spin_unlock_irqrestore(&report_filterlist_lock, flags);
+ return ret;
+}
+
+static void set_report_filterlist_whitelist(bool whitelist)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&report_filterlist_lock, flags);
+ report_filterlist.whitelist = whitelist;
+ spin_unlock_irqrestore(&report_filterlist_lock, flags);
+}
+
+static void insert_report_filterlist(const char *func)
+{
+ unsigned long flags;
+ unsigned long addr = kallsyms_lookup_name(func);
+
+ if (!addr) {
+ pr_err("KCSAN: could not find function: '%s'\n", func);
+ return;
+ }
+
+ spin_lock_irqsave(&report_filterlist_lock, flags);
+
+ if (report_filterlist.addrs == NULL)
+ report_filterlist.addrs = /* initial allocation */
+ kvmalloc_array(report_filterlist.size,
+ sizeof(unsigned long), GFP_KERNEL);
+ else if (report_filterlist.used == report_filterlist.size) {
+ /* resize filterlist */
+ unsigned long *new_addrs;
+
+ report_filterlist.size *= 2;
+ new_addrs = kvmalloc_array(report_filterlist.size,
+ sizeof(unsigned long), GFP_KERNEL);
+ memcpy(new_addrs, report_filterlist.addrs,
+ report_filterlist.used * sizeof(unsigned long));
+ kvfree(report_filterlist.addrs);
+ report_filterlist.addrs = new_addrs;
+ }
+
+ /* Note: deduplicating should be done in userspace. */
+ report_filterlist.addrs[report_filterlist.used++] =
+ kallsyms_lookup_name(func);
+ report_filterlist.sorted = false;
+
+ spin_unlock_irqrestore(&report_filterlist_lock, flags);
+}
+
+static int show_info(struct seq_file *file, void *v)
+{
+ int i;
+ unsigned long flags;
+
+ /* show stats */
+ seq_printf(file, "enabled: %i\n", READ_ONCE(kcsan_enabled));
+ for (i = 0; i < kcsan_counter_count; ++i)
+ seq_printf(file, "%s: %ld\n", counter_to_name(i),
+ atomic_long_read(&counters[i]));
+
+ /* show filter functions, and filter type */
+ spin_lock_irqsave(&report_filterlist_lock, flags);
+ seq_printf(file, "\n%s functions: %s\n",
+ report_filterlist.whitelist ? "whitelisted" : "blacklisted",
+ report_filterlist.used == 0 ? "none" : "");
+ for (i = 0; i < report_filterlist.used; ++i)
+ seq_printf(file, " %ps\n", (void *)report_filterlist.addrs[i]);
+ spin_unlock_irqrestore(&report_filterlist_lock, flags);
+
+ return 0;
+}
+
+static int debugfs_open(struct inode *inode, struct file *file)
+{
+ return single_open(file, show_info, NULL);
+}
+
+static ssize_t debugfs_write(struct file *file, const char __user *buf,
+ size_t count, loff_t *off)
+{
+ char kbuf[KSYM_NAME_LEN];
+ char *arg;
+ int read_len = count < (sizeof(kbuf) - 1) ? count : (sizeof(kbuf) - 1);
+
+ if (copy_from_user(kbuf, buf, read_len))
+ return -EINVAL;
+ kbuf[read_len] = '\0';
+ arg = strstrip(kbuf);
+
+ if (!strncmp(arg, "on", sizeof("on") - 1))
+ WRITE_ONCE(kcsan_enabled, true);
+ else if (!strncmp(arg, "off", sizeof("off") - 1))
+ WRITE_ONCE(kcsan_enabled, false);
+ else if (!strncmp(arg, "whitelist", sizeof("whitelist") - 1))
+ set_report_filterlist_whitelist(true);
+ else if (!strncmp(arg, "blacklist", sizeof("blacklist") - 1))
+ set_report_filterlist_whitelist(false);
+ else if (arg[0] == '!')
+ insert_report_filterlist(&arg[1]);
+ else
+ return -EINVAL;
+
+ return count;
+}
+
+static const struct file_operations debugfs_ops = { .read = seq_read,
+ .open = debugfs_open,
+ .write = debugfs_write,
+ .release = single_release };
+
+void __init kcsan_debugfs_init(void)
+{
+ debugfs_create_file("kcsan", 0644, NULL, NULL, &debugfs_ops);
+}
diff --git a/kernel/kcsan/encoding.h b/kernel/kcsan/encoding.h
new file mode 100644
index 000000000000..8f9b1ce0e59f
--- /dev/null
+++ b/kernel/kcsan/encoding.h
@@ -0,0 +1,94 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _MM_KCSAN_ENCODING_H
+#define _MM_KCSAN_ENCODING_H
+
+#include <linux/bits.h>
+#include <linux/log2.h>
+#include <linux/mm.h>
+
+#include "kcsan.h"
+
+#define SLOT_RANGE PAGE_SIZE
+#define INVALID_WATCHPOINT 0
+#define CONSUMED_WATCHPOINT 1
+
+/*
+ * The maximum useful size of accesses for which we set up watchpoints is the
+ * max range of slots we check on an access.
+ */
+#define MAX_ENCODABLE_SIZE (SLOT_RANGE * (1 + KCSAN_CHECK_ADJACENT))
+
+/*
+ * Number of bits we use to store size info.
+ */
+#define WATCHPOINT_SIZE_BITS bits_per(MAX_ENCODABLE_SIZE)
+/*
+ * This encoding for addresses discards the upper (1 for is-write + SIZE_BITS);
+ * however, most 64-bit architectures do not use the full 64-bit address space.
+ * Also, in order for a false positive to be observable 2 things need to happen:
+ *
+ * 1. different addresses but with the same encoded address race;
+ * 2. and both map onto the same watchpoint slots;
+ *
+ * Both these are assumed to be very unlikely. However, in case it still happens
+ * happens, the report logic will filter out the false positive (see report.c).
+ */
+#define WATCHPOINT_ADDR_BITS (BITS_PER_LONG - 1 - WATCHPOINT_SIZE_BITS)
+
+/*
+ * Masks to set/retrieve the encoded data.
+ */
+#define WATCHPOINT_WRITE_MASK BIT(BITS_PER_LONG - 1)
+#define WATCHPOINT_SIZE_MASK \
+ GENMASK(BITS_PER_LONG - 2, BITS_PER_LONG - 2 - WATCHPOINT_SIZE_BITS)
+#define WATCHPOINT_ADDR_MASK \
+ GENMASK(BITS_PER_LONG - 3 - WATCHPOINT_SIZE_BITS, 0)
+
+static inline bool check_encodable(unsigned long addr, size_t size)
+{
+ return size <= MAX_ENCODABLE_SIZE;
+}
+
+static inline long encode_watchpoint(unsigned long addr, size_t size,
+ bool is_write)
+{
+ return (long)((is_write ? WATCHPOINT_WRITE_MASK : 0) |
+ (size << WATCHPOINT_ADDR_BITS) |
+ (addr & WATCHPOINT_ADDR_MASK));
+}
+
+static inline bool decode_watchpoint(long watchpoint,
+ unsigned long *addr_masked, size_t *size,
+ bool *is_write)
+{
+ if (watchpoint == INVALID_WATCHPOINT ||
+ watchpoint == CONSUMED_WATCHPOINT)
+ return false;
+
+ *addr_masked = (unsigned long)watchpoint & WATCHPOINT_ADDR_MASK;
+ *size = ((unsigned long)watchpoint & WATCHPOINT_SIZE_MASK) >>
+ WATCHPOINT_ADDR_BITS;
+ *is_write = !!((unsigned long)watchpoint & WATCHPOINT_WRITE_MASK);
+
+ return true;
+}
+
+/*
+ * Return watchpoint slot for an address.
+ */
+static inline int watchpoint_slot(unsigned long addr)
+{
+ return (addr / PAGE_SIZE) % KCSAN_NUM_WATCHPOINTS;
+}
+
+static inline bool matching_access(unsigned long addr1, size_t size1,
+ unsigned long addr2, size_t size2)
+{
+ unsigned long end_range1 = addr1 + size1 - 1;
+ unsigned long end_range2 = addr2 + size2 - 1;
+
+ return addr1 <= end_range2 && addr2 <= end_range1;
+}
+
+#endif /* _MM_KCSAN_ENCODING_H */
diff --git a/kernel/kcsan/kcsan.c b/kernel/kcsan/kcsan.c
new file mode 100644
index 000000000000..45cf2fffd8a0
--- /dev/null
+++ b/kernel/kcsan/kcsan.c
@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * The Kernel Concurrency Sanitizer (KCSAN) infrastructure. For more info please
+ * see Documentation/dev-tools/kcsan.rst.
+ */
+
+#include <linux/export.h>
+
+#include "kcsan.h"
+
+/*
+ * KCSAN uses the same instrumentation that is emitted by supported compilers
+ * for Thread Sanitizer (TSAN).
+ *
+ * When enabled, the compiler emits instrumentation calls (the functions
+ * prefixed with "__tsan" below) for all loads and stores that it generated;
+ * inline asm is not instrumented.
+ */
+
+#define DEFINE_TSAN_READ_WRITE(size) \
+ void __tsan_read##size(void *ptr) \
+ { \
+ __kcsan_check_read(ptr, size); \
+ } \
+ EXPORT_SYMBOL(__tsan_read##size); \
+ void __tsan_write##size(void *ptr) \
+ { \
+ __kcsan_check_write(ptr, size); \
+ } \
+ EXPORT_SYMBOL(__tsan_write##size)
+
+DEFINE_TSAN_READ_WRITE(1);
+DEFINE_TSAN_READ_WRITE(2);
+DEFINE_TSAN_READ_WRITE(4);
+DEFINE_TSAN_READ_WRITE(8);
+DEFINE_TSAN_READ_WRITE(16);
+
+/*
+ * Not all supported compiler versions distinguish aligned/unaligned accesses,
+ * but e.g. recent versions of Clang do.
+ */
+#define DEFINE_TSAN_UNALIGNED_READ_WRITE(size) \
+ void __tsan_unaligned_read##size(void *ptr) \
+ { \
+ __kcsan_check_read(ptr, size); \
+ } \
+ EXPORT_SYMBOL(__tsan_unaligned_read##size); \
+ void __tsan_unaligned_write##size(void *ptr) \
+ { \
+ __kcsan_check_write(ptr, size); \
+ } \
+ EXPORT_SYMBOL(__tsan_unaligned_write##size)
+
+DEFINE_TSAN_UNALIGNED_READ_WRITE(2);
+DEFINE_TSAN_UNALIGNED_READ_WRITE(4);
+DEFINE_TSAN_UNALIGNED_READ_WRITE(8);
+DEFINE_TSAN_UNALIGNED_READ_WRITE(16);
+
+void __tsan_read_range(void *ptr, size_t size)
+{
+ __kcsan_check_read(ptr, size);
+}
+EXPORT_SYMBOL(__tsan_read_range);
+
+void __tsan_write_range(void *ptr, size_t size)
+{
+ __kcsan_check_write(ptr, size);
+}
+EXPORT_SYMBOL(__tsan_write_range);
+
+/*
+ * The below are not required KCSAN, but can still be emitted by the compiler.
+ */
+void __tsan_func_entry(void *call_pc)
+{
+}
+EXPORT_SYMBOL(__tsan_func_entry);
+void __tsan_func_exit(void)
+{
+}
+EXPORT_SYMBOL(__tsan_func_exit);
+void __tsan_init(void)
+{
+}
+EXPORT_SYMBOL(__tsan_init);
diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h
new file mode 100644
index 000000000000..429479b3041d
--- /dev/null
+++ b/kernel/kcsan/kcsan.h
@@ -0,0 +1,140 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _MM_KCSAN_KCSAN_H
+#define _MM_KCSAN_KCSAN_H
+
+#include <linux/kcsan.h>
+
+/*
+ * Total number of watchpoints. An address range maps into a specific slot as
+ * specified in `encoding.h`. Although larger number of watchpoints may not even
+ * be usable due to limited thread count, a larger value will improve
+ * performance due to reducing cache-line contention.
+ */
+#define KCSAN_NUM_WATCHPOINTS 64
+
+/*
+ * The number of adjacent watchpoints to check; the purpose is 2-fold:
+ *
+ * 1. the address slot is already occupied, check if any adjacent slots are
+ * free;
+ * 2. accesses that straddle a slot boundary due to size that exceeds a
+ * slot's range may check adjacent slots if any watchpoint matches.
+ *
+ * Note that accesses with very large size may still miss a watchpoint; however,
+ * given this should be rare, this is a reasonable trade-off to make, since this
+ * will avoid:
+ *
+ * 1. excessive contention between watchpoint checks and setup;
+ * 2. larger number of simultaneous watchpoints without sacrificing
+ * performance.
+ */
+#define KCSAN_CHECK_ADJACENT 1
+
+/*
+ * Globally enable and disable KCSAN.
+ */
+extern bool kcsan_enabled;
+
+/*
+ * Helper that returns true if access to ptr should be considered as an atomic
+ * access, even though it is not explicitly atomic.
+ */
+bool kcsan_is_atomic(const volatile void *ptr);
+
+/*
+ * Initialize debugfs file.
+ */
+void kcsan_debugfs_init(void);
+
+enum kcsan_counter_id {
+ /*
+ * Number of watchpoints currently in use.
+ */
+ kcsan_counter_used_watchpoints,
+
+ /*
+ * Total number of watchpoints set up.
+ */
+ kcsan_counter_setup_watchpoints,
+
+ /*
+ * Total number of data-races.
+ */
+ kcsan_counter_data_races,
+
+ /*
+ * Number of times no watchpoints were available.
+ */
+ kcsan_counter_no_capacity,
+
+ /*
+ * A thread checking a watchpoint raced with another checking thread;
+ * only one will be reported.
+ */
+ kcsan_counter_report_races,
+
+ /*
+ * Observed data value change, but writer thread unknown.
+ */
+ kcsan_counter_races_unknown_origin,
+
+ /*
+ * The access cannot be encoded to a valid watchpoint.
+ */
+ kcsan_counter_unencodable_accesses,
+
+ /*
+ * Watchpoint encoding caused a watchpoint to fire on mismatching
+ * accesses.
+ */
+ kcsan_counter_encoding_false_positives,
+
+ kcsan_counter_count, /* number of counters */
+};
+
+/*
+ * Increment/decrement counter with given id; avoid calling these in fast-path.
+ */
+void kcsan_counter_inc(enum kcsan_counter_id id);
+void kcsan_counter_dec(enum kcsan_counter_id id);
+
+/*
+ * Returns true if data-races in the function symbol that maps to addr (offsets
+ * are ignored) should *not* be reported.
+ */
+bool kcsan_skip_report(unsigned long func_addr);
+
+enum kcsan_report_type {
+ /*
+ * The thread that set up the watchpoint and briefly stalled was
+ * signalled that another thread triggered the watchpoint, and thus a
+ * race was encountered.
+ */
+ kcsan_report_race_setup,
+
+ /*
+ * A thread encountered a watchpoint for the access, therefore a race
+ * was encountered.
+ */
+ kcsan_report_race_check,
+
+ /*
+ * A thread encountered a watchpoint for the access, but the other
+ * racing thread can no longer be signaled that a race occurred.
+ */
+ kcsan_report_race_check_race,
+
+ /*
+ * No other thread was observed to race with the access, but the data
+ * value before and after the stall differs.
+ */
+ kcsan_report_race_unknown_origin,
+};
+/*
+ * Print a race report from thread that encountered the race.
+ */
+void kcsan_report(const volatile void *ptr, size_t size, bool is_write,
+ int cpu_id, enum kcsan_report_type type);
+
+#endif /* _MM_KCSAN_KCSAN_H */
diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
new file mode 100644
index 000000000000..517db539e4e7
--- /dev/null
+++ b/kernel/kcsan/report.c
@@ -0,0 +1,306 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/kernel.h>
+#include <linux/preempt.h>
+#include <linux/printk.h>
+#include <linux/sched.h>
+#include <linux/spinlock.h>
+#include <linux/stacktrace.h>
+
+#include "kcsan.h"
+#include "encoding.h"
+
+/*
+ * Max. number of stack entries to show in the report.
+ */
+#define NUM_STACK_ENTRIES 16
+
+/*
+ * Other thread info: communicated from other racing thread to thread that set
+ * up the watchpoint, which then prints the complete report atomically. Only
+ * need one struct, as all threads should to be serialized regardless to print
+ * the reports, with reporting being in the slow-path.
+ */
+static struct {
+ const volatile void *ptr;
+ size_t size;
+ bool is_write;
+ int task_pid;
+ int cpu_id;
+ unsigned long stack_entries[NUM_STACK_ENTRIES];
+ int num_stack_entries;
+} other_info = { .ptr = NULL };
+
+static DEFINE_SPINLOCK(other_info_lock);
+static DEFINE_SPINLOCK(report_lock);
+
+static bool set_or_lock_other_info(unsigned long *flags,
+ const volatile void *ptr, size_t size,
+ bool is_write, int cpu_id,
+ enum kcsan_report_type type)
+{
+ if (type != kcsan_report_race_check && type != kcsan_report_race_setup)
+ return true;
+
+ for (;;) {
+ spin_lock_irqsave(&other_info_lock, *flags);
+
+ switch (type) {
+ case kcsan_report_race_check:
+ if (other_info.ptr != NULL) {
+ /* still in use, retry */
+ break;
+ }
+ other_info.ptr = ptr;
+ other_info.size = size;
+ other_info.is_write = is_write;
+ other_info.task_pid =
+ in_task() ? task_pid_nr(current) : -1;
+ other_info.cpu_id = cpu_id;
+ other_info.num_stack_entries = stack_trace_save(
+ other_info.stack_entries, NUM_STACK_ENTRIES, 1);
+ /*
+ * other_info may now be consumed by thread we raced
+ * with.
+ */
+ spin_unlock_irqrestore(&other_info_lock, *flags);
+ return false;
+
+ case kcsan_report_race_setup:
+ if (other_info.ptr == NULL)
+ break; /* no data available yet, retry */
+
+ /*
+ * First check if matching based on how watchpoint was
+ * encoded.
+ */
+ if (!matching_access((unsigned long)other_info.ptr &
+ WATCHPOINT_ADDR_MASK,
+ other_info.size,
+ (unsigned long)ptr &
+ WATCHPOINT_ADDR_MASK,
+ size))
+ break; /* mismatching access, retry */
+
+ if (!matching_access((unsigned long)other_info.ptr,
+ other_info.size,
+ (unsigned long)ptr, size)) {
+ /*
+ * If the actual accesses to not match, this was
+ * a false positive due to watchpoint encoding.
+ */
+ other_info.ptr = NULL; /* mark for reuse */
+ kcsan_counter_inc(
+ kcsan_counter_encoding_false_positives);
+ spin_unlock_irqrestore(&other_info_lock,
+ *flags);
+ return false;
+ }
+
+ /*
+ * Matching access: keep other_info locked, as this
+ * thread uses it to print the full report; unlocked in
+ * end_report.
+ */
+ return true;
+
+ default:
+ BUG();
+ }
+
+ spin_unlock_irqrestore(&other_info_lock, *flags);
+ }
+}
+
+static void start_report(unsigned long *flags, enum kcsan_report_type type)
+{
+ switch (type) {
+ case kcsan_report_race_setup:
+ /* irqsaved already via other_info_lock */
+ spin_lock(&report_lock);
+ break;
+
+ case kcsan_report_race_unknown_origin:
+ spin_lock_irqsave(&report_lock, *flags);
+ break;
+
+ default:
+ BUG();
+ }
+}
+
+static void end_report(unsigned long *flags, enum kcsan_report_type type)
+{
+ switch (type) {
+ case kcsan_report_race_setup:
+ other_info.ptr = NULL; /* mark for reuse */
+ spin_unlock(&report_lock);
+ spin_unlock_irqrestore(&other_info_lock, *flags);
+ break;
+
+ case kcsan_report_race_unknown_origin:
+ spin_unlock_irqrestore(&report_lock, *flags);
+ break;
+
+ default:
+ BUG();
+ }
+}
+
+static const char *get_access_type(bool is_write)
+{
+ return is_write ? "write" : "read";
+}
+
+/* Return thread description: in task or interrupt. */
+static const char *get_thread_desc(int task_id)
+{
+ if (task_id != -1) {
+ static char buf[32]; /* safe: protected by report_lock */
+
+ snprintf(buf, sizeof(buf), "task %i", task_id);
+ return buf;
+ }
+ return in_nmi() ? "NMI" : "interrupt";
+}
+
+/* Helper to skip KCSAN-related functions in stack-trace. */
+static int get_stack_skipnr(unsigned long stack_entries[], int num_entries)
+{
+ char buf[64];
+ int skip = 0;
+
+ for (; skip < num_entries; ++skip) {
+ snprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skip]);
+ if (!strnstr(buf, "csan_", sizeof(buf)) &&
+ !strnstr(buf, "tsan_", sizeof(buf)) &&
+ !strnstr(buf, "_once_size", sizeof(buf))) {
+ break;
+ }
+ }
+ return skip;
+}
+
+/* Compares symbolized strings of addr1 and addr2. */
+static int sym_strcmp(void *addr1, void *addr2)
+{
+ char buf1[64];
+ char buf2[64];
+
+ snprintf(buf1, sizeof(buf1), "%pS", addr1);
+ snprintf(buf2, sizeof(buf2), "%pS", addr2);
+ return strncmp(buf1, buf2, sizeof(buf1));
+}
+
+/*
+ * Returns true if a report was generated, false otherwise.
+ */
+static bool print_summary(const volatile void *ptr, size_t size, bool is_write,
+ int cpu_id, enum kcsan_report_type type)
+{
+ unsigned long stack_entries[NUM_STACK_ENTRIES] = { 0 };
+ int num_stack_entries =
+ stack_trace_save(stack_entries, NUM_STACK_ENTRIES, 1);
+ int skipnr = get_stack_skipnr(stack_entries, num_stack_entries);
+ int other_skipnr;
+
+ /* Check if the top stackframe is in a blacklisted function. */
+ if (kcsan_skip_report(stack_entries[skipnr]))
+ return false;
+ if (type == kcsan_report_race_setup) {
+ other_skipnr = get_stack_skipnr(other_info.stack_entries,
+ other_info.num_stack_entries);
+ if (kcsan_skip_report(other_info.stack_entries[other_skipnr]))
+ return false;
+ }
+
+ /* Print report header. */
+ pr_err("==================================================================\n");
+ switch (type) {
+ case kcsan_report_race_setup: {
+ void *this_fn = (void *)stack_entries[skipnr];
+ void *other_fn = (void *)other_info.stack_entries[other_skipnr];
+ int cmp;
+
+ /*
+ * Order functions lexographically for consistent bug titles.
+ * Do not print offset of functions to keep title short.
+ */
+ cmp = sym_strcmp(other_fn, this_fn);
+ pr_err("BUG: KCSAN: data-race in %ps / %ps\n",
+ cmp < 0 ? other_fn : this_fn,
+ cmp < 0 ? this_fn : other_fn);
+ } break;
+
+ case kcsan_report_race_unknown_origin:
+ pr_err("BUG: KCSAN: data-race in %pS\n",
+ (void *)stack_entries[skipnr]);
+ break;
+
+ default:
+ BUG();
+ }
+
+ pr_err("\n");
+
+ /* Print information about the racing accesses. */
+ switch (type) {
+ case kcsan_report_race_setup:
+ pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
+ get_access_type(other_info.is_write), other_info.ptr,
+ other_info.size, get_thread_desc(other_info.task_pid),
+ other_info.cpu_id);
+
+ /* Print the other thread's stack trace. */
+ stack_trace_print(other_info.stack_entries + other_skipnr,
+ other_info.num_stack_entries - other_skipnr,
+ 0);
+
+ pr_err("\n");
+ pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n",
+ get_access_type(is_write), ptr, size,
+ get_thread_desc(in_task() ? task_pid_nr(current) : -1),
+ cpu_id);
+ break;
+
+ case kcsan_report_race_unknown_origin:
+ pr_err("race at unknown origin, with %s to 0x%px of %zu bytes by %s on cpu %i:\n",
+ get_access_type(is_write), ptr, size,
+ get_thread_desc(in_task() ? task_pid_nr(current) : -1),
+ cpu_id);
+ break;
+
+ default:
+ BUG();
+ }
+ /* Print stack trace of this thread. */
+ stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr,
+ 0);
+
+ /* Print report footer. */
+ pr_err("\n");
+ pr_err("Reported by Kernel Concurrency Sanitizer on:\n");
+ dump_stack_print_info(KERN_DEFAULT);
+ pr_err("==================================================================\n");
+
+ return true;
+}
+
+void kcsan_report(const volatile void *ptr, size_t size, bool is_write,
+ int cpu_id, enum kcsan_report_type type)
+{
+ unsigned long flags = 0;
+
+ if (type == kcsan_report_race_check_race)
+ return;
+
+ kcsan_disable_current();
+ if (set_or_lock_other_info(&flags, ptr, size, is_write, cpu_id, type)) {
+ start_report(&flags, type);
+ if (print_summary(ptr, size, is_write, cpu_id, type) &&
+ panic_on_warn)
+ panic("panic_on_warn set ...\n");
+ end_report(&flags, type);
+ }
+ kcsan_enable_current();
+}
diff --git a/kernel/kcsan/test.c b/kernel/kcsan/test.c
new file mode 100644
index 000000000000..68c896a24529
--- /dev/null
+++ b/kernel/kcsan/test.c
@@ -0,0 +1,117 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/printk.h>
+#include <linux/random.h>
+#include <linux/types.h>
+
+#include "encoding.h"
+
+#define ITERS_PER_TEST 2000
+
+/* Test requirements. */
+static bool test_requires(void)
+{
+ /* random should be initialized */
+ return prandom_u32() + prandom_u32() != 0;
+}
+
+/* Test watchpoint encode and decode. */
+static bool test_encode_decode(void)
+{
+ int i;
+
+ for (i = 0; i < ITERS_PER_TEST; ++i) {
+ size_t size = prandom_u32() % MAX_ENCODABLE_SIZE + 1;
+ bool is_write = prandom_u32() % 2;
+ unsigned long addr;
+
+ prandom_bytes(&addr, sizeof(addr));
+ if (WARN_ON(!check_encodable(addr, size)))
+ return false;
+
+ /* encode and decode */
+ {
+ const long encoded_watchpoint =
+ encode_watchpoint(addr, size, is_write);
+ unsigned long verif_masked_addr;
+ size_t verif_size;
+ bool verif_is_write;
+
+ /* check special watchpoints */
+ if (WARN_ON(decode_watchpoint(
+ INVALID_WATCHPOINT, &verif_masked_addr,
+ &verif_size, &verif_is_write)))
+ return false;
+ if (WARN_ON(decode_watchpoint(
+ CONSUMED_WATCHPOINT, &verif_masked_addr,
+ &verif_size, &verif_is_write)))
+ return false;
+
+ /* check decoding watchpoint returns same data */
+ if (WARN_ON(!decode_watchpoint(
+ encoded_watchpoint, &verif_masked_addr,
+ &verif_size, &verif_is_write)))
+ return false;
+ if (WARN_ON(verif_masked_addr !=
+ (addr & WATCHPOINT_ADDR_MASK)))
+ goto fail;
+ if (WARN_ON(verif_size != size))
+ goto fail;
+ if (WARN_ON(is_write != verif_is_write))
+ goto fail;
+
+ continue;
+fail:
+ pr_err("%s fail: %s %zu bytes @ %lx -> encoded: %lx -> %s %zu bytes @ %lx\n",
+ __func__, is_write ? "write" : "read", size,
+ addr, encoded_watchpoint,
+ verif_is_write ? "write" : "read", verif_size,
+ verif_masked_addr);
+ return false;
+ }
+ }
+
+ return true;
+}
+
+static bool test_matching_access(void)
+{
+ if (WARN_ON(!matching_access(10, 1, 10, 1)))
+ return false;
+ if (WARN_ON(!matching_access(10, 2, 11, 1)))
+ return false;
+ if (WARN_ON(!matching_access(10, 1, 9, 2)))
+ return false;
+ if (WARN_ON(matching_access(10, 1, 11, 1)))
+ return false;
+ if (WARN_ON(matching_access(9, 1, 10, 1)))
+ return false;
+ return true;
+}
+
+static int __init kcsan_selftest(void)
+{
+ int passed = 0;
+ int total = 0;
+
+#define RUN_TEST(do_test) \
+ do { \
+ ++total; \
+ if (do_test()) \
+ ++passed; \
+ else \
+ pr_err("KCSAN selftest: " #do_test " failed"); \
+ } while (0)
+
+ RUN_TEST(test_requires);
+ RUN_TEST(test_encode_decode);
+ RUN_TEST(test_matching_access);
+
+ pr_info("KCSAN selftest: %d/%d tests passed\n", passed, total);
+ if (passed != total)
+ panic("KCSAN selftests failed");
+ return 0;
+}
+postcore_initcall(kcsan_selftest);
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 93d97f9b0157..35accd1d93de 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -2086,6 +2086,8 @@ source "lib/Kconfig.kgdb"
source "lib/Kconfig.ubsan"
+source "lib/Kconfig.kcsan"
+
config ARCH_HAS_DEVMEM_IS_ALLOWED
bool
diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
new file mode 100644
index 000000000000..3e1f1acfb24b
--- /dev/null
+++ b/lib/Kconfig.kcsan
@@ -0,0 +1,88 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+config HAVE_ARCH_KCSAN
+ bool
+
+menuconfig KCSAN
+ bool "KCSAN: watchpoint-based dynamic data-race detector"
+ depends on HAVE_ARCH_KCSAN && !KASAN && STACKTRACE
+ default n
+ help
+ Kernel Concurrency Sanitizer is a dynamic data-race detector, which
+ uses a watchpoint-based sampling approach to detect races.
+
+if KCSAN
+
+config KCSAN_SELFTEST
+ bool "KCSAN: perform short selftests on boot"
+ default y
+ help
+ Run KCSAN selftests on boot. On test failure, causes kernel to panic.
+
+config KCSAN_EARLY_ENABLE
+ bool "KCSAN: early enable"
+ default y
+ help
+ If KCSAN should be enabled globally as soon as possible. KCSAN can
+ later be enabled/disabled via debugfs.
+
+config KCSAN_UDELAY_MAX_TASK
+ int "KCSAN: maximum delay in microseconds (for tasks)"
+ default 80
+ help
+ For tasks, the max. microsecond delay after setting up a watchpoint.
+
+config KCSAN_UDELAY_MAX_INTERRUPT
+ int "KCSAN: maximum delay in microseconds (for interrupts)"
+ default 20
+ help
+ For interrupts, the max. microsecond delay after setting up a watchpoint.
+
+config KCSAN_DELAY_RANDOMIZE
+ bool "KCSAN: randomize delays"
+ default y
+ help
+ If delays should be randomized; if false, the chosen delay is simply
+ the maximum values defined above.
+
+config KCSAN_WATCH_SKIP_INST
+ int "KCSAN: watchpoint instruction skip"
+ default 2000
+ help
+ The number of per-CPU memory operations to skip watching, before
+ another watchpoint is set up; in other words, 1 in
+ KCSAN_WATCH_SKIP_INST per-CPU memory operations are used to set up a
+ watchpoint. A smaller value results in more aggressive race
+ detection, whereas a larger value improves system performance at the
+ cost of missing some races.
+
+config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
+ bool "KCSAN: report races of unknown origin"
+ default y
+ help
+ If KCSAN should report races where only one access is known, and the
+ conflicting access is of unknown origin. This type of race is
+ reported if it was only possible to infer a race due to a data-value
+ change while an access is being delayed on a watchpoint.
+
+config KCSAN_IGNORE_ATOMICS
+ bool "KCSAN: do not instrument marked atomic accesses"
+ default n
+ help
+ If enabled, never instruments marked atomic accesses. This results in
+ not reporting data-races where one access is atomic and the other is
+ a plain access.
+
+config KCSAN_PLAIN_WRITE_PRETEND_ONCE
+ bool "KCSAN: pretend plain writes are WRITE_ONCE"
+ default n
+ help
+ This option makes KCSAN pretend that all plain writes are WRITE_ONCE.
+ This option should only be used to prune initial data-races found in
+ existing code.
+
+config KCSAN_DEBUG
+ bool "Debugging of KCSAN internals"
+ default n
+
+endif # KCSAN
diff --git a/lib/Makefile b/lib/Makefile
index c5892807e06f..778ab704e3ad 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -24,6 +24,9 @@ KASAN_SANITIZE_string.o := n
CFLAGS_string.o := $(call cc-option, -fno-stack-protector)
endif
+# Used by KCSAN while enabled, avoid recursion.
+KCSAN_SANITIZE_random32.o := n
+
lib-y := ctype.o string.o vsprintf.o cmdline.o \
rbtree.o radix-tree.o timerqueue.o xarray.o \
idr.o extable.o \
diff --git a/scripts/Makefile.kcsan b/scripts/Makefile.kcsan
new file mode 100644
index 000000000000..caf1111a28ae
--- /dev/null
+++ b/scripts/Makefile.kcsan
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+ifdef CONFIG_KCSAN
+
+CFLAGS_KCSAN := -fsanitize=thread
+
+endif # CONFIG_KCSAN
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index 179d55af5852..0e78abab7d83 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -152,6 +152,16 @@ _c_flags += $(if $(patsubst n%,, \
$(CFLAGS_KCOV))
endif
+#
+# Enable ConcurrencySanitizer flags for kernel except some files or directories
+# we don't want to check (depends on variables KCSAN_SANITIZE_obj.o, KCSAN_SANITIZE)
+#
+ifeq ($(CONFIG_KCSAN),y)
+_c_flags += $(if $(patsubst n%,, \
+ $(KCSAN_SANITIZE_$(basetarget).o)$(KCSAN_SANITIZE)y), \
+ $(CFLAGS_KCSAN))
+endif
+
# $(srctree)/$(src) for including checkin headers from generated source files
# $(objtree)/$(obj) for including generated headers from checkin source files
ifeq ($(KBUILD_EXTMOD),)
--
2.23.0.866.gb869b98d4c-goog
