[PATCH 1/8] kcsan: Add Kernel Concurrency Sanitizer infrastructure

[Marco Elver]

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>
---
 Documentation/dev-tools/kcsan.rst | 202 +++++++++++++
 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      | 116 ++++++++
 include/linux/kcsan.h             |  85 ++++++
 include/linux/sched.h             |   7 +
 init/init_task.c                  |   6 +
 init/main.c                       |   2 +
 kernel/Makefile                   |   1 +
 kernel/kcsan/Makefile             |  14 +
 kernel/kcsan/atomic.c             |  21 ++
 kernel/kcsan/core.c               | 458 ++++++++++++++++++++++++++++++
 kernel/kcsan/debugfs.c            | 225 +++++++++++++++
 kernel/kcsan/encoding.h           |  94 ++++++
 kernel/kcsan/kcsan.c              |  81 ++++++
 kernel/kcsan/kcsan.h              | 140 +++++++++
 kernel/kcsan/report.c             | 307 ++++++++++++++++++++
 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, 2041 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..5b46cc5593c3
--- /dev/null
+++ b/Documentation/dev-tools/kcsan.rst
@@ -0,0 +1,202 @@
+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: racing read 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. **Performance Overhead:** KCSAN's runtime is minimal, and does not require
+   locking shared state for each access. This results in significantly better
+   performance in comparison with KTSAN.
+
+2. **Memory Overhead:** No shadow memory is required. The current
+   implementation uses a small array of longs to encode watchpoint information,
+   which is negligible.
+
+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 such as KTSAN.
+
+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..0a7467477f84 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((const void *)p, size, false);
+	__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((const void *)p, size, true);
+
 	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..bee619b66e1c
--- /dev/null
+++ b/include/linux/kcsan-checks.h
@@ -0,0 +1,116 @@
+/* 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_access - check regular access for data-races
+ *
+ * Full access that checks watchpoint and sets up a watchpoint if this access is
+ * sampled.
+ *
+ * @ptr address of access
+ * @size size of access
+ * @is_write is access a write
+ */
+#define __kcsan_check_access(ptr, size, is_write)                              \
+	do {                                                                   \
+		if (__kcsan_check_watchpoint(ptr, size, is_write) &&           \
+		    !(IS_ENABLED(CONFIG_KCSAN_PLAIN_WRITE_PRETEND_ONCE) &&     \
+		      is_write))                                               \
+			__kcsan_setup_watchpoint(ptr, size, is_write);         \
+	} while (0)
+/**
+ * kcsan_check_access - check regular access for data-races
+ *
+ * @ptr address of access
+ * @size size of access
+ * @is_write is access a write
+ */
+#define kcsan_check_access(ptr, size, is_write)                                \
+	do {                                                                   \
+		if (kcsan_check_watchpoint(ptr, size, is_write) &&             \
+		    !(IS_ENABLED(CONFIG_KCSAN_PLAIN_WRITE_PRETEND_ONCE) &&     \
+		      is_write))                                               \
+			kcsan_setup_watchpoint(ptr, size, is_write);           \
+	} while (0)
+
+/*
+ * Check for atomic accesses: if atomics are not ignored, this simply aliases to
+ * kcsan_check_watchpoint, otherwise becomes a no-op.
+ */
+#ifdef CONFIG_KCSAN_IGNORE_ATOMICS
+#define kcsan_check_atomic(...)                                                \
+	do {                                                                   \
+	} while (0)
+#else
+#define kcsan_check_atomic kcsan_check_watchpoint
+#endif
+
+#endif /* _LINUX_KCSAN_CHECKS_H */
diff --git a/include/linux/kcsan.h b/include/linux/kcsan.h
new file mode 100644
index 000000000000..18c660628376
--- /dev/null
+++ b/include/linux/kcsan.h
@@ -0,0 +1,85 @@
+/* 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
+
+/**
+ * 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..34a1d9310304 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1171,6 +1171,13 @@ struct task_struct {
 #ifdef CONFIG_KASAN
 	unsigned int			kasan_depth;
 #endif
+#ifdef CONFIG_KCSAN
+	/* See comments at kernel/kcsan/core.c: struct cpu_state. */
+	int				kcsan_disable;
+	int				kcsan_atomic_next;
+	int				kcsan_atomic_region;
+	bool				kcsan_atomic_region_flat;
+#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..f98fc4c9f635 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -161,6 +161,12 @@ struct task_struct init_task
 #ifdef CONFIG_KASAN
 	.kasan_depth	= 1,
 #endif
+#ifdef CONFIG_KCSAN
+	.kcsan_disable			= 1,
+	.kcsan_atomic_next		= 0,
+	.kcsan_atomic_region		= 0,
+	.kcsan_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..e8c3823bf7c4
--- /dev/null
+++ b/kernel/kcsan/core.c
@@ -0,0 +1,458 @@
+// 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 state that should be used instead of 'current' if we are not in a
+ * task.
+ */
+struct cpu_state {
+	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;
+};
+static DEFINE_PER_CPU(struct cpu_state, this_state) = {
+	.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 bool is_atomic(const volatile void *ptr)
+{
+	if (in_task()) {
+		if (unlikely(current->kcsan_atomic_next > 0)) {
+			--current->kcsan_atomic_next;
+			return true;
+		}
+		if (unlikely(current->kcsan_atomic_region > 0 ||
+			     current->kcsan_atomic_region_flat))
+			return true;
+	} else { /* interrupt */
+		if (unlikely(this_cpu_read(this_state.atomic_next) > 0)) {
+			this_cpu_dec(this_state.atomic_next);
+			return true;
+		}
+		if (unlikely(this_cpu_read(this_state.atomic_region) > 0 ||
+			     this_cpu_read(this_state.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) &&
+	       (in_task() ? current->kcsan_disable :
+			    this_cpu_read(this_state.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)
+{
+	if (in_task())
+		++current->kcsan_disable;
+	else
+		this_cpu_inc(this_state.disable);
+}
+EXPORT_SYMBOL(kcsan_disable_current);
+
+void kcsan_enable_current(void)
+{
+	int prev = in_task() ? current->kcsan_disable-- :
+			       (this_cpu_dec_return(this_state.disable) + 1);
+	if (prev == 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) {
+		if (in_task())
+			++current->kcsan_atomic_region;
+		else
+			this_cpu_inc(this_state.atomic_region);
+	} else {
+		if (in_task())
+			current->kcsan_atomic_region_flat = true;
+		else
+			this_cpu_write(this_state.atomic_region_flat, true);
+	}
+}
+EXPORT_SYMBOL(kcsan_begin_atomic);
+
+void kcsan_end_atomic(bool nest)
+{
+	if (nest) {
+		int prev =
+			in_task() ?
+				current->kcsan_atomic_region-- :
+				(this_cpu_dec_return(this_state.atomic_region) +
+				 1);
+		if (prev == 0) {
+			kcsan_begin_atomic(true); /* restore to 0 */
+			kcsan_disable_current();
+			WARN(1, "mismatching %s", __func__);
+			kcsan_enable_current();
+		}
+	} else {
+		if (in_task())
+			current->kcsan_atomic_region_flat = false;
+		else
+			this_cpu_write(this_state.atomic_region_flat, false);
+	}
+}
+EXPORT_SYMBOL(kcsan_end_atomic);
+
+void kcsan_atomic_next(int n)
+{
+	if (in_task())
+		current->kcsan_atomic_next = n;
+	else
+		this_cpu_write(this_state.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;
+
+	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 ignore races due to accesses in
+	 * threads running on the same CPU.
+	 */
+	local_irq_save(irq_flags);
+	preempt_disable();
+
+	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:
+	preempt_enable();
+	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..ce13e0b38ba2
--- /dev/null
+++ b/kernel/kcsan/kcsan.c
@@ -0,0 +1,81 @@
+// 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"
+
+/*
+ * Concurrency Sanitizer uses the same instrumentation as Thread Sanitizer.
+ */
+
+#define DEFINE_TSAN_READ_WRITE(size)                                           \
+	void __tsan_read##size(void *ptr)                                      \
+	{                                                                      \
+		__kcsan_check_access(ptr, size, false);                        \
+	}                                                                      \
+	EXPORT_SYMBOL(__tsan_read##size);                                      \
+	void __tsan_write##size(void *ptr)                                     \
+	{                                                                      \
+		__kcsan_check_access(ptr, size, true);                         \
+	}                                                                      \
+	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_access(ptr, size, false);                        \
+	}                                                                      \
+	EXPORT_SYMBOL(__tsan_unaligned_read##size);                            \
+	void __tsan_unaligned_write##size(void *ptr)                           \
+	{                                                                      \
+		__kcsan_check_access(ptr, size, true);                         \
+	}                                                                      \
+	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_access(ptr, size, false);
+}
+EXPORT_SYMBOL(__tsan_read_range);
+
+void __tsan_write_range(void *ptr, size_t size)
+{
+	__kcsan_check_access(ptr, size, true);
+}
+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..1a0f34b623bf
--- /dev/null
+++ b/kernel/kcsan/report.c
@@ -0,0 +1,307 @@
+// 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: racing %s in %pS\n",
+		       get_access_type(is_write),
+		       (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..b532d0d98f7a
--- /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 atomic accesses"
+	default n
+	help
+	  If enabled, never instruments 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),)
-- 
2.23.0.700.g56cf767bdb-goog