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Subject[PATCH v4 01/10] kcsan: Add Kernel Concurrency Sanitizer infrastructure
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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@google.com>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
---
v4:
* Performance optimizations:
- Avoid modulo in SLOT_IDX in fast-path: introduce SLOT_IDX_FAST.
- Further fast-path optimizations by moving more code into slow-path.
=> 33% faster compared to v3 (using microbenchmark).
* compiler.h: Fix __no_sanitize_thread for GCC 4.9 in regular build.
* Deal with nested interrupts for atomic_next.
* Sort headers that were not sorted in new files.
* Add more comments.
* Simplify report.c (removing double-locking as well), in preparation
for KCSAN_REPORT_VALUE_CHANGE_ONLY.
* Introduce KCSAN_REPORT_VALUE_CHANGE_ONLY option for further filtering of data
races: if a conflicting write was observed via a watchpoint, only
report the data race if a value change was observed as well. The
option will be enabled by default on syzbot. (rcu-functions will be
excluded from this filter at request of Paul McKenney.) Context:
http://lkml.kernel.org/r/CANpmjNOepvb6+zJmDePxj21n2rctM4Sp4rJ66x_J-L1UmNK54A@mail.gmail.com

v3:
* Move Documentation to separate patch.
* Default init_task 'disable_count' to 0, since kcsan_enabled is sufficient.
* Fix CFLAGS for compilers that do not support all options.
* lib/Kconfig.kcsan:
- Clarify preference of config option over boot param in comment.
- Add ref to Documentation
- Remove unnecessary "KCSAN:"
* include/linux/compiler.h: Remove (const void*) casts
* include/linux/kcsan.h:
- Reword atomic nestable and flat region comment, and clarify that they
are independent.
- Rename atomic_region -> atomic_nest_count.
- Rename atomic_region_flat -> in_flat_atomic.
- Rename kcsan_{begin,end}_atomic -> kcsan_{nestable,flat}_atomic_{begin,end}
* kernel/kcsan/kcsan.h:
- Capitalize enums.
- Make KCSAN_NUM_WATCHPOINTS configurable -> lib/Kconfig.kcsan.
* Make kcsan_is_atomic inlinable by turning atomic.c into atomic.h.
* kernel/kcsan/core.c (merged with previous kcsan.c):
- Make __tsan_unaligned __alias of generic accesses.
- user_access_save/restore() usage comment.
- Add instruction watchpoint skip randomization.
- Refactor API and core runtime fast-path and slow-path; check_access is
now the single entry point for checking an access. Compared to the
previous version, with a default config and benchmarked using the
microbenchmark, this version is 3.8x faster.
* kernel/kcsan/test.c: Add more comments where appropriate.
* kernel/kcsan/report.c:
- get_thread_desc should just return "interrupt" for any interrupt.
- increase NUM_STACK_ENTRIES to 64.
* kernel/kcsan/debugfs.c
- More appropriate error codes.
- Use kmalloc+krealloc instead of kvmalloc.
- Handle kmalloc failures.
- Add debugfs based microbenchmark.
* Use '{ }' on same line where appropriate.
* Prefer IS_ENABLED instead of #ifdef.
* Use common spelling: "data-race" -> "data race"
* Other typos.

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].
---
MAINTAINERS | 11 +
Makefile | 3 +-
include/linux/compiler-clang.h | 9 +
include/linux/compiler-gcc.h | 7 +
include/linux/compiler.h | 37 +-
include/linux/kcsan-checks.h | 97 +++++
include/linux/kcsan.h | 115 ++++++
include/linux/sched.h | 4 +
init/init_task.c | 8 +
init/main.c | 2 +
kernel/Makefile | 1 +
kernel/kcsan/Makefile | 11 +
kernel/kcsan/atomic.h | 27 ++
kernel/kcsan/core.c | 626 +++++++++++++++++++++++++++++++++
kernel/kcsan/debugfs.c | 275 +++++++++++++++
kernel/kcsan/encoding.h | 94 +++++
kernel/kcsan/kcsan.h | 108 ++++++
kernel/kcsan/report.c | 320 +++++++++++++++++
kernel/kcsan/test.c | 121 +++++++
lib/Kconfig.debug | 2 +
lib/Kconfig.kcsan | 118 +++++++
lib/Makefile | 3 +
scripts/Makefile.kcsan | 6 +
scripts/Makefile.lib | 10 +
24 files changed, 2006 insertions(+), 9 deletions(-)
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.h
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.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/MAINTAINERS b/MAINTAINERS
index f77959ecf7e0..36e74531e969 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -8848,6 +8848,17 @@ F: Documentation/kbuild/kconfig*
F: scripts/kconfig/
F: scripts/Kconfig.include

+KCSAN
+M: Marco Elver <elver@google.com>
+R: Dmitry Vyukov <dvyukov@google.com>
+L: kasan-dev@googlegroups.com
+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@redhat.com>
M: Baoquan He <bhe@redhat.com>
diff --git a/Makefile b/Makefile
index 42bfda209cb8..4cd27e0c8fc0 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..0eb2a1cc411d 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -145,6 +145,13 @@
#define __no_sanitize_address
#endif

+#if defined(__SANITIZE_THREAD__) && __has_attribute(__no_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..c42fa83f23fb 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
@@ -207,18 +202,44 @@ void __read_once_size(const volatile void *p, void *res, int size)
* '__maybe_unused' allows us to avoid defined-but-not-used warnings.
*/
# define __no_kasan_or_inline __no_sanitize_address notrace __maybe_unused
+# define __no_sanitize_or_inline __no_kasan_or_inline
#else
# define __no_kasan_or_inline __always_inline
#endif

-static __no_kasan_or_inline
+#ifdef __SANITIZE_THREAD__
+/*
+ * Rely on __SANITIZE_THREAD__ instead of CONFIG_KCSAN, to avoid not inlining in
+ * compilation units where instrumentation is disabled.
+ */
+# define __no_kcsan_or_inline __no_sanitize_thread notrace __maybe_unused
+# define __no_sanitize_or_inline __no_kcsan_or_inline
+#else
+# define __no_kcsan_or_inline __always_inline
+#endif
+
+#ifndef __no_sanitize_or_inline
+#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(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(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..e78220661086
--- /dev/null
+++ b/include/linux/kcsan-checks.h
@@ -0,0 +1,97 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_KCSAN_CHECKS_H
+#define _LINUX_KCSAN_CHECKS_H
+
+#include <linux/types.h>
+
+/*
+ * Access type modifiers.
+ */
+#define KCSAN_ACCESS_WRITE 0x1
+#define KCSAN_ACCESS_ATOMIC 0x2
+
+/*
+ * __kcsan_*: Always calls into runtime 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_access - check generic access for data race
+ *
+ * @ptr address of access
+ * @size size of access
+ * @type access type modifier
+ */
+void __kcsan_check_access(const volatile void *ptr, size_t size, int type);
+
+#else
+static inline void __kcsan_check_access(const volatile void *ptr, size_t size,
+ int type) { }
+#endif
+
+/*
+ * kcsan_*: Only calls into runtime when the particular compilation unit has
+ * KCSAN instrumentation enabled. May be used in header files.
+ */
+#ifdef __SANITIZE_THREAD__
+#define kcsan_check_access __kcsan_check_access
+#else
+static inline void kcsan_check_access(const volatile void *ptr, size_t size,
+ int type) { }
+#endif
+
+/**
+ * __kcsan_check_read - check regular read access for data races
+ *
+ * @ptr address of access
+ * @size size of access
+ */
+#define __kcsan_check_read(ptr, size) __kcsan_check_access(ptr, size, 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) \
+ __kcsan_check_access(ptr, size, KCSAN_ACCESS_WRITE)
+
+/**
+ * kcsan_check_read - check regular read access for data races
+ *
+ * @ptr address of access
+ * @size size of access
+ */
+#define kcsan_check_read(ptr, size) kcsan_check_access(ptr, size, 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) \
+ kcsan_check_access(ptr, size, KCSAN_ACCESS_WRITE)
+
+/*
+ * Check for atomic accesses: if atomic access are not ignored, this simply
+ * aliases to kcsan_check_access, 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_access(ptr, size, KCSAN_ACCESS_ATOMIC)
+#define kcsan_check_atomic_write(ptr, size) \
+ kcsan_check_access(ptr, size, KCSAN_ACCESS_ATOMIC | KCSAN_ACCESS_WRITE)
+#endif
+
+#endif /* _LINUX_KCSAN_CHECKS_H */
diff --git a/include/linux/kcsan.h b/include/linux/kcsan.h
new file mode 100644
index 000000000000..9047048fee84
--- /dev/null
+++ b/include/linux/kcsan.h
@@ -0,0 +1,115 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_KCSAN_H
+#define _LINUX_KCSAN_H
+
+#include <linux/kcsan-checks.h>
+#include <linux/types.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_count; /* disable counter */
+ int atomic_next; /* number of following atomic ops */
+
+ /*
+ * We distinguish between: (a) nestable atomic regions that may contain
+ * other nestable regions; and (b) flat atomic regions that do not keep
+ * track of nesting. Both (a) and (b) are entirely independent of each
+ * other, and a flat region may be started in a nestable region or
+ * vice-versa.
+ *
+ * This is required because, for example, in the annotations for
+ * seqlocks, we declare seqlock writer critical sections as (a) nestable
+ * atomic regions, but reader critical sections as (b) flat atomic
+ * regions, but have encountered cases where seqlock reader critical
+ * sections are contained within writer critical sections (the opposite
+ * may be possible, too).
+ *
+ * To support these cases, we independently track the depth of nesting
+ * for (a), and whether the leaf level is flat for (b).
+ */
+ int atomic_nest_count;
+ bool in_flat_atomic;
+};
+
+/**
+ * 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_nestable_atomic_begin - begin nestable atomic region
+ *
+ * Accesses within the atomic region may appear to race with other accesses but
+ * should be considered atomic.
+ */
+void kcsan_nestable_atomic_begin(void);
+
+/**
+ * kcsan_nestable_atomic_end - end nestable atomic region
+ */
+void kcsan_nestable_atomic_end(void);
+
+/**
+ * kcsan_flat_atomic_begin - begin flat atomic region
+ *
+ * Accesses within the atomic region may appear to race with other accesses but
+ * should be considered atomic.
+ */
+void kcsan_flat_atomic_begin(void);
+
+/**
+ * kcsan_flat_atomic_end - end flat atomic region
+ */
+void kcsan_flat_atomic_end(void);
+
+/**
+ * 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_nestable_atomic_begin(void) { }
+
+static inline void kcsan_nestable_atomic_end(void) { }
+
+static inline void kcsan_flat_atomic_begin(void) { }
+
+static inline void kcsan_flat_atomic_end(void) { }
+
+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 67a1d86981a9..ae4f341c1db4 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;
@@ -1172,6 +1173,9 @@ 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..2b4fe98b0f09 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_count = 0,
+ .atomic_next = 0,
+ .atomic_nest_count = 0,
+ .in_flat_atomic = false,
+ },
+#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..dd15b62ec0b5
--- /dev/null
+++ b/kernel/kcsan/Makefile
@@ -0,0 +1,11 @@
+# SPDX-License-Identifier: GPL-2.0
+KCSAN_SANITIZE := n
+KCOV_INSTRUMENT := n
+
+CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE)
+
+CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) \
+ $(call cc-option,-fno-stack-protector,)
+
+obj-y := core.o debugfs.o report.o
+obj-$(CONFIG_KCSAN_SELFTEST) += test.o
diff --git a/kernel/kcsan/atomic.h b/kernel/kcsan/atomic.h
new file mode 100644
index 000000000000..c9c3fe628011
--- /dev/null
+++ b/kernel/kcsan/atomic.h
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _KERNEL_KCSAN_ATOMIC_H
+#define _KERNEL_KCSAN_ATOMIC_H
+
+#include <linux/jiffies.h>
+
+/*
+ * Helper that returns true if access to ptr should be considered as an atomic
+ * access, even though it is not explicitly atomic.
+ *
+ * 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.
+ */
+static inline bool kcsan_is_atomic(const volatile void *ptr)
+{
+ /* only jiffies for now */
+ return ptr == &jiffies;
+}
+
+#endif /* _KERNEL_KCSAN_ATOMIC_H */
diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
new file mode 100644
index 000000000000..d9410d58c93e
--- /dev/null
+++ b/kernel/kcsan/core.c
@@ -0,0 +1,626 @@
+// 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 "atomic.h"
+#include "encoding.h"
+#include "kcsan.h"
+
+bool kcsan_enabled;
+
+/* Per-CPU kcsan_ctx for interrupts */
+static DEFINE_PER_CPU(struct kcsan_ctx, kcsan_cpu_ctx) = {
+ .disable_count = 0,
+ .atomic_next = 0,
+ .atomic_nest_count = 0,
+ .in_flat_atomic = false,
+};
+
+/*
+ * Helper macros to index into adjacent slots slots, starting from address slot
+ * itself, followed by the right and left slots.
+ *
+ * The purpose is 2-fold:
+ *
+ * 1. if during insertion 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.
+ *
+ * Example: SLOT_IDX values for KCSAN_CHECK_ADJACENT=1, where i is [0, 1, 2]:
+ *
+ * slot=0: [ 1, 2, 0]
+ * slot=9: [10, 11, 9]
+ * slot=63: [64, 65, 63]
+ */
+#define NUM_SLOTS (1 + 2 * KCSAN_CHECK_ADJACENT)
+#define SLOT_IDX(slot, i) (slot + ((i + KCSAN_CHECK_ADJACENT) % NUM_SLOTS))
+
+/*
+ * SLOT_IDX_FAST is used in fast-path. Not first checking the address's primary
+ * slot (middle) is fine if we assume that data races occur rarely. The set of
+ * indices {SLOT_IDX(slot, i) | i in [0, NUM_SLOTS)} is equivalent to
+ * {SLOT_IDX_FAST(slot, i) | i in [0, NUM_SLOTS)}.
+ */
+#define SLOT_IDX_FAST(slot, i) (slot + i)
+
+/*
+ * 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.
+ *
+ * Add NUM_SLOTS-1 entries to account for overflow; this helps avoid having to
+ * use more complicated SLOT_IDX_FAST calculation with modulo in fast-path.
+ */
+static atomic_long_t watchpoints[CONFIG_KCSAN_NUM_WATCHPOINTS + NUM_SLOTS - 1];
+
+/*
+ * Instructions to skip watching counter, used in should_watch(). We use a
+ * per-CPU counter to avoid excessive contention.
+ */
+static DEFINE_PER_CPU(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;
+
+ BUILD_BUG_ON(CONFIG_KCSAN_NUM_WATCHPOINTS < NUM_SLOTS);
+
+ for (i = 0; i < NUM_SLOTS; ++i) {
+ watchpoint = &watchpoints[SLOT_IDX_FAST(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;
+
+ /* Check slot index logic, ensuring we stay within array bounds. */
+ BUILD_BUG_ON(SLOT_IDX(0, 0) != KCSAN_CHECK_ADJACENT);
+ BUILD_BUG_ON(SLOT_IDX(0, KCSAN_CHECK_ADJACENT + 1) != 0);
+ BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS - 1,
+ KCSAN_CHECK_ADJACENT) !=
+ ARRAY_SIZE(watchpoints) - 1);
+ BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS - 1,
+ KCSAN_CHECK_ADJACENT + 1) !=
+ ARRAY_SIZE(watchpoints) - NUM_SLOTS);
+
+ for (i = 0; i < 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() ? &current->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)) {
+ /*
+ * Because we do not have separate contexts for nested
+ * interrupts, in case atomic_next is set, we simply assume that
+ * the outer interrupt set atomic_next. In the worst case, we
+ * will conservatively consider operations as atomic. This is a
+ * reasonable trade-off to make, since this case should be
+ * extremely rare; however, even if extremely rare, it could
+ * lead to false positives otherwise.
+ */
+ if ((hardirq_count() >> HARDIRQ_SHIFT) < 2)
+ --ctx->atomic_next; /* in task, or outer interrupt */
+ return true;
+ }
+ if (unlikely(ctx->atomic_nest_count > 0 || ctx->in_flat_atomic))
+ return true;
+
+ return kcsan_is_atomic(ptr);
+}
+
+static inline bool should_watch(const volatile void *ptr, int type)
+{
+ /*
+ * Never set up watchpoints when memory operations are atomic.
+ *
+ * Need to check this first, before kcsan_skip check below: (1) atomics
+ * should not count towards skipped instructions, and (2) to actually
+ * decrement kcsan_atomic_next for consecutive instruction stream.
+ */
+ if ((type & KCSAN_ACCESS_ATOMIC) != 0 || is_atomic(ptr))
+ return false;
+
+ if (this_cpu_dec_return(kcsan_skip) >= 0)
+ return false;
+
+ /*
+ * NOTE: If we get here, kcsan_skip must always be reset in slow path
+ * via reset_kcsan_skip() to avoid underflow.
+ */
+
+ /* this operation should be watched */
+ return true;
+}
+
+static inline void reset_kcsan_skip(void)
+{
+ long skip_count = CONFIG_KCSAN_SKIP_WATCH -
+ (IS_ENABLED(CONFIG_KCSAN_SKIP_WATCH_RANDOMIZE) ?
+ prandom_u32_max(CONFIG_KCSAN_SKIP_WATCH) :
+ 0);
+ this_cpu_write(kcsan_skip, skip_count);
+}
+
+static inline bool kcsan_is_enabled(void)
+{
+ return READ_ONCE(kcsan_enabled) && get_ctx()->disable_count == 0;
+}
+
+static inline unsigned int get_delay(void)
+{
+ unsigned int delay = in_task() ? CONFIG_KCSAN_UDELAY_TASK :
+ CONFIG_KCSAN_UDELAY_INTERRUPT;
+ return delay - (IS_ENABLED(CONFIG_KCSAN_DELAY_RANDOMIZE) ?
+ prandom_u32_max(delay) :
+ 0);
+}
+
+/*
+ * Pull everything together: check_access() below contains the performance
+ * critical operations; the fast-path (including check_access) functions should
+ * all be inlinable by the instrumentation functions.
+ *
+ * The slow-path (kcsan_found_watchpoint, kcsan_setup_watchpoint) are
+ * non-inlinable -- note that, we prefix these with "kcsan_" to ensure they can
+ * be filtered from the stacktrace, as well as give them unique names for the
+ * UACCESS whitelist of objtool. Each function uses user_access_save/restore(),
+ * since they do not access any user memory, but instrumentation is still
+ * emitted in UACCESS regions.
+ */
+
+static noinline void kcsan_found_watchpoint(const volatile void *ptr,
+ size_t size, bool is_write,
+ atomic_long_t *watchpoint,
+ long encoded_watchpoint)
+{
+ unsigned long flags;
+ bool consumed;
+
+ if (!kcsan_is_enabled())
+ return;
+ /*
+ * Consume the watchpoint as soon as possible, to minimize the chances
+ * of !consumed. Consuming the watchpoint must always be guarded by
+ * kcsan_is_enabled() check, as otherwise we might erroneously
+ * triggering reports when disabled.
+ */
+ consumed = try_consume_watchpoint(watchpoint, encoded_watchpoint);
+
+ /* keep this after try_consume_watchpoint */
+ flags = user_access_save();
+
+ if (consumed) {
+ kcsan_report(ptr, size, is_write, true, raw_smp_processor_id(),
+ KCSAN_REPORT_CONSUMED_WATCHPOINT);
+ } else {
+ /*
+ * 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);
+ }
+ kcsan_counter_inc(KCSAN_COUNTER_DATA_RACES);
+
+ user_access_restore(flags);
+}
+
+static noinline 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 value_change = false;
+ unsigned long ua_flags = user_access_save();
+ unsigned long irq_flags;
+
+ /*
+ * Always reset kcsan_skip counter in slow-path to avoid underflow; see
+ * should_watch().
+ */
+ reset_kcsan_skip();
+
+ if (!kcsan_is_enabled())
+ 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 point of view) 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 */
+ }
+
+ if (IS_ENABLED(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();
+ }
+
+ /*
+ * 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:
+ value_change = expect_value._1 != READ_ONCE(*(const u8 *)ptr);
+ break;
+ case 2:
+ value_change = expect_value._2 != READ_ONCE(*(const u16 *)ptr);
+ break;
+ case 4:
+ value_change = expect_value._4 != READ_ONCE(*(const u32 *)ptr);
+ break;
+ case 8:
+ value_change = 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 'data_races' counter, as the racing
+ * thread already did.
+ */
+ kcsan_report(ptr, size, is_write, size > 8 || value_change,
+ smp_processor_id(), KCSAN_REPORT_RACE_SIGNAL);
+ } else if (value_change) {
+ /* Inferring a race, since the value should not have changed. */
+ kcsan_counter_inc(KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN);
+ if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN))
+ kcsan_report(ptr, size, is_write, true,
+ smp_processor_id(),
+ KCSAN_REPORT_RACE_UNKNOWN_ORIGIN);
+ }
+
+ kcsan_counter_dec(KCSAN_COUNTER_USED_WATCHPOINTS);
+out_unlock:
+ local_irq_restore(irq_flags);
+out:
+ user_access_restore(ua_flags);
+}
+
+static __always_inline void check_access(const volatile void *ptr, size_t size,
+ int type)
+{
+ const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0;
+ atomic_long_t *watchpoint;
+ long encoded_watchpoint;
+
+ /*
+ * Avoid user_access_save in fast-path: 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);
+ /*
+ * It is safe to check kcsan_is_enabled() after find_watchpoint in the
+ * slow-path, as long as no state changes that cause a data race to be
+ * detected and reported have occurred until kcsan_is_enabled() is
+ * checked.
+ */
+
+ if (unlikely(watchpoint != NULL))
+ kcsan_found_watchpoint(ptr, size, is_write, watchpoint,
+ encoded_watchpoint);
+ else if (unlikely(should_watch(ptr, type)))
+ kcsan_setup_watchpoint(ptr, size, is_write);
+}
+
+/* === Public interface ===================================================== */
+
+void __init kcsan_init(void)
+{
+ BUG_ON(!in_task());
+
+ kcsan_debugfs_init();
+
+ /*
+ * We are in the init task, and no other tasks should be running;
+ * WRITE_ONCE without memory barrier is sufficient.
+ */
+ if (IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE))
+ WRITE_ONCE(kcsan_enabled, true);
+}
+
+/* === Exported interface =================================================== */
+
+void kcsan_disable_current(void)
+{
+ ++get_ctx()->disable_count;
+}
+EXPORT_SYMBOL(kcsan_disable_current);
+
+void kcsan_enable_current(void)
+{
+ if (get_ctx()->disable_count-- == 0) {
+ /*
+ * Warn if kcsan_enable_current() calls are unbalanced with
+ * kcsan_disable_current() calls, which causes disable_count to
+ * become negative and should not happen.
+ */
+ kcsan_disable_current(); /* restore to 0, KCSAN still enabled */
+ kcsan_disable_current(); /* disable to generate warning */
+ WARN(1, "Unbalanced %s()", __func__);
+ kcsan_enable_current();
+ }
+}
+EXPORT_SYMBOL(kcsan_enable_current);
+
+void kcsan_nestable_atomic_begin(void)
+{
+ /*
+ * Do *not* check and warn if we are in a flat atomic region: nestable
+ * and flat atomic regions are independent from each other.
+ * See include/linux/kcsan.h: struct kcsan_ctx comments for more
+ * comments.
+ */
+
+ ++get_ctx()->atomic_nest_count;
+}
+EXPORT_SYMBOL(kcsan_nestable_atomic_begin);
+
+void kcsan_nestable_atomic_end(void)
+{
+ if (get_ctx()->atomic_nest_count-- == 0) {
+ /*
+ * Warn if kcsan_nestable_atomic_end() calls are unbalanced with
+ * kcsan_nestable_atomic_begin() calls, which causes
+ * atomic_nest_count to become negative and should not happen.
+ */
+ kcsan_nestable_atomic_begin(); /* restore to 0 */
+ kcsan_disable_current(); /* disable to generate warning */
+ WARN(1, "Unbalanced %s()", __func__);
+ kcsan_enable_current();
+ }
+}
+EXPORT_SYMBOL(kcsan_nestable_atomic_end);
+
+void kcsan_flat_atomic_begin(void)
+{
+ get_ctx()->in_flat_atomic = true;
+}
+EXPORT_SYMBOL(kcsan_flat_atomic_begin);
+
+void kcsan_flat_atomic_end(void)
+{
+ get_ctx()->in_flat_atomic = false;
+}
+EXPORT_SYMBOL(kcsan_flat_atomic_end);
+
+void kcsan_atomic_next(int n)
+{
+ get_ctx()->atomic_next = n;
+}
+EXPORT_SYMBOL(kcsan_atomic_next);
+
+void __kcsan_check_access(const volatile void *ptr, size_t size, int type)
+{
+ check_access(ptr, size, type);
+}
+EXPORT_SYMBOL(__kcsan_check_access);
+
+/*
+ * KCSAN uses the same instrumentation that is emitted by supported compilers
+ * for ThreadSanitizer (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.
+ *
+ * Note that, not all supported compiler versions distinguish aligned/unaligned
+ * accesses, but e.g. recent versions of Clang do. We simply alias the unaligned
+ * version to the generic version, which can handle both.
+ */
+
+#define DEFINE_TSAN_READ_WRITE(size) \
+ void __tsan_read##size(void *ptr) \
+ { \
+ check_access(ptr, size, 0); \
+ } \
+ EXPORT_SYMBOL(__tsan_read##size); \
+ void __tsan_unaligned_read##size(void *ptr) \
+ __alias(__tsan_read##size); \
+ EXPORT_SYMBOL(__tsan_unaligned_read##size); \
+ void __tsan_write##size(void *ptr) \
+ { \
+ check_access(ptr, size, KCSAN_ACCESS_WRITE); \
+ } \
+ EXPORT_SYMBOL(__tsan_write##size); \
+ void __tsan_unaligned_write##size(void *ptr) \
+ __alias(__tsan_write##size); \
+ EXPORT_SYMBOL(__tsan_unaligned_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);
+
+void __tsan_read_range(void *ptr, size_t size)
+{
+ check_access(ptr, size, 0);
+}
+EXPORT_SYMBOL(__tsan_read_range);
+
+void __tsan_write_range(void *ptr, size_t size)
+{
+ check_access(ptr, size, KCSAN_ACCESS_WRITE);
+}
+EXPORT_SYMBOL(__tsan_write_range);
+
+/*
+ * The below are not required by 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/debugfs.c b/kernel/kcsan/debugfs.c
new file mode 100644
index 000000000000..041d520a0183
--- /dev/null
+++ b/kernel/kcsan/debugfs.c
@@ -0,0 +1,275 @@
+// 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/seq_file.h>
+#include <linux/slab.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]);
+}
+
+/*
+ * The microbenchmark allows benchmarking KCSAN core runtime only. To run
+ * multiple threads, pipe 'microbench=<iters>' from multiple tasks into the
+ * debugfs file.
+ */
+static void microbenchmark(unsigned long iters)
+{
+ cycles_t cycles;
+
+ pr_info("KCSAN: %s begin | iters: %lu\n", __func__, iters);
+
+ cycles = get_cycles();
+ while (iters--) {
+ /*
+ * We can run this benchmark from multiple tasks; this address
+ * calculation increases likelyhood of some accesses overlapping
+ * (they still won't conflict because all are reads).
+ */
+ unsigned long addr =
+ iters % (CONFIG_KCSAN_NUM_WATCHPOINTS * PAGE_SIZE);
+ __kcsan_check_read((void *)addr, sizeof(long));
+ }
+ cycles = get_cycles() - cycles;
+
+ pr_info("KCSAN: %s end | cycles: %llu\n", __func__, cycles);
+}
+
+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_debugfs(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);
+}
+
+/* Returns 0 on success, error-code otherwise. */
+static ssize_t insert_report_filterlist(const char *func)
+{
+ unsigned long flags;
+ unsigned long addr = kallsyms_lookup_name(func);
+ ssize_t ret = 0;
+
+ if (!addr) {
+ pr_err("KCSAN: could not find function: '%s'\n", func);
+ return -ENOENT;
+ }
+
+ spin_lock_irqsave(&report_filterlist_lock, flags);
+
+ if (report_filterlist.addrs == NULL) {
+ /* initial allocation */
+ report_filterlist.addrs =
+ kmalloc_array(report_filterlist.size,
+ sizeof(unsigned long), GFP_KERNEL);
+ if (report_filterlist.addrs == NULL) {
+ ret = -ENOMEM;
+ goto out;
+ }
+ } else if (report_filterlist.used == report_filterlist.size) {
+ /* resize filterlist */
+ size_t new_size = report_filterlist.size * 2;
+ unsigned long *new_addrs =
+ krealloc(report_filterlist.addrs,
+ new_size * sizeof(unsigned long), GFP_KERNEL);
+
+ if (new_addrs == NULL) {
+ /* leave filterlist itself untouched */
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ report_filterlist.size = new_size;
+ 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;
+
+out:
+ spin_unlock_irqrestore(&report_filterlist_lock, flags);
+ return ret;
+}
+
+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 -EFAULT;
+ kbuf[read_len] = '\0';
+ arg = strstrip(kbuf);
+
+ if (!strcmp(arg, "on")) {
+ WRITE_ONCE(kcsan_enabled, true);
+ } else if (!strcmp(arg, "off")) {
+ WRITE_ONCE(kcsan_enabled, false);
+ } else if (!strncmp(arg, "microbench=", sizeof("microbench=") - 1)) {
+ unsigned long iters;
+
+ if (kstrtoul(&arg[sizeof("microbench=") - 1], 0, &iters))
+ return -EINVAL;
+ microbenchmark(iters);
+ } else if (!strcmp(arg, "whitelist")) {
+ set_report_filterlist_whitelist(true);
+ } else if (!strcmp(arg, "blacklist")) {
+ set_report_filterlist_whitelist(false);
+ } else if (arg[0] == '!') {
+ ssize_t ret = insert_report_filterlist(&arg[1]);
+
+ if (ret < 0)
+ return ret;
+ } 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..e17bdac0e54b
--- /dev/null
+++ b/kernel/kcsan/encoding.h
@@ -0,0 +1,94 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _KERNEL_KCSAN_ENCODING_H
+#define _KERNEL_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) % CONFIG_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 /* _KERNEL_KCSAN_ENCODING_H */
diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h
new file mode 100644
index 000000000000..1bb2f1c0d61e
--- /dev/null
+++ b/kernel/kcsan/kcsan.h
@@ -0,0 +1,108 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * The Kernel Concurrency Sanitizer (KCSAN) infrastructure. For more info please
+ * see Documentation/dev-tools/kcsan.rst.
+ */
+
+#ifndef _KERNEL_KCSAN_KCSAN_H
+#define _KERNEL_KCSAN_KCSAN_H
+
+#include <linux/kcsan.h>
+
+/* The number of adjacent watchpoints to check. */
+#define KCSAN_CHECK_ADJACENT 1
+
+/*
+ * Globally enable and disable KCSAN.
+ */
+extern bool kcsan_enabled;
+
+/*
+ * 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 func_addr
+ * (offsets are ignored) should *not* be reported.
+ */
+bool kcsan_skip_report_debugfs(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.
+ */
+ KCSAN_REPORT_RACE_SIGNAL,
+
+ /*
+ * A thread found and consumed a matching watchpoint.
+ */
+ KCSAN_REPORT_CONSUMED_WATCHPOINT,
+
+ /*
+ * 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,
+ bool value_change, int cpu_id, enum kcsan_report_type type);
+
+#endif /* _KERNEL_KCSAN_KCSAN_H */
diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
new file mode 100644
index 000000000000..ead5610bafa7
--- /dev/null
+++ b/kernel/kcsan/report.c
@@ -0,0 +1,320 @@
+// 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 64
+
+/*
+ * 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 };
+
+/*
+ * This spinlock protects reporting and other_info, since other_info is usually
+ * required when reporting.
+ */
+static DEFINE_SPINLOCK(report_lock);
+
+/*
+ * Special rules to skip reporting.
+ */
+static bool skip_report(bool is_write, bool value_change,
+ unsigned long top_frame)
+{
+ if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) && is_write &&
+ !value_change) {
+ /*
+ * The access is a write, but the data value did not change.
+ *
+ * We opt-out of this filter for certain functions at request of
+ * maintainers.
+ */
+ char buf[64];
+
+ snprintf(buf, sizeof(buf), "%ps", (void *)top_frame);
+ if (!strnstr(buf, "rcu_", sizeof(buf)) &&
+ !strnstr(buf, "_rcu", sizeof(buf)) &&
+ !strnstr(buf, "_srcu", sizeof(buf)))
+ return true;
+ }
+
+ return kcsan_skip_report_debugfs(top_frame);
+}
+
+static inline 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 "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_report(const volatile void *ptr, size_t size, bool is_write,
+ bool value_change, 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;
+
+ /*
+ * Must check report filter rules before starting to print.
+ */
+ if (skip_report(is_write, true, stack_entries[skipnr]))
+ return false;
+
+ if (type == KCSAN_REPORT_RACE_SIGNAL) {
+ other_skipnr = get_stack_skipnr(other_info.stack_entries,
+ other_info.num_stack_entries);
+
+ /* value_change is only known for the other thread */
+ if (skip_report(other_info.is_write, value_change,
+ other_info.stack_entries[other_skipnr]))
+ return false;
+ }
+
+ /* Print report header. */
+ pr_err("==================================================================\n");
+ switch (type) {
+ case KCSAN_REPORT_RACE_SIGNAL: {
+ 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_SIGNAL:
+ 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;
+}
+
+static void release_report(unsigned long *flags, enum kcsan_report_type type)
+{
+ if (type == KCSAN_REPORT_RACE_SIGNAL)
+ other_info.ptr = NULL; /* mark for reuse */
+
+ spin_unlock_irqrestore(&report_lock, *flags);
+}
+
+/*
+ * Depending on the report type either sets other_info and returns false, or
+ * acquires the matching other_info and returns true. If other_info is not
+ * required for the report type, simply acquires report_lock and returns true.
+ */
+static bool prepare_report(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_CONSUMED_WATCHPOINT &&
+ type != KCSAN_REPORT_RACE_SIGNAL) {
+ /* other_info not required; just acquire report_lock */
+ spin_lock_irqsave(&report_lock, *flags);
+ return true;
+ }
+
+retry:
+ spin_lock_irqsave(&report_lock, *flags);
+
+ switch (type) {
+ case KCSAN_REPORT_CONSUMED_WATCHPOINT:
+ if (other_info.ptr != NULL)
+ break; /* still in use, retry */
+
+ 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);
+
+ spin_unlock_irqrestore(&report_lock, *flags);
+
+ /*
+ * The other thread will print the summary; other_info may now
+ * be consumed.
+ */
+ return false;
+
+ case KCSAN_REPORT_RACE_SIGNAL:
+ if (other_info.ptr == NULL)
+ break; /* no data available yet, retry */
+
+ /*
+ * First check if this is the other_info we are expecting, i.e.
+ * matches 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 watchpoint, 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.
+ */
+ kcsan_counter_inc(
+ KCSAN_COUNTER_ENCODING_FALSE_POSITIVES);
+
+ /* discard this other_info */
+ release_report(flags, KCSAN_REPORT_RACE_SIGNAL);
+ return false;
+ }
+
+ /*
+ * Matching & usable access in other_info: keep other_info_lock
+ * locked, as this thread consumes it to print the full report;
+ * unlocked in release_report.
+ */
+ return true;
+
+ default:
+ BUG();
+ }
+
+ spin_unlock_irqrestore(&report_lock, *flags);
+ goto retry;
+}
+
+void kcsan_report(const volatile void *ptr, size_t size, bool is_write,
+ bool value_change, int cpu_id, enum kcsan_report_type type)
+{
+ unsigned long flags = 0;
+
+ kcsan_disable_current();
+ if (prepare_report(&flags, ptr, size, is_write, cpu_id, type)) {
+ if (print_report(ptr, size, is_write, value_change, cpu_id,
+ type) &&
+ panic_on_warn)
+ panic("panic_on_warn set ...\n");
+
+ release_report(&flags, type);
+ }
+ kcsan_enable_current();
+}
diff --git a/kernel/kcsan/test.c b/kernel/kcsan/test.c
new file mode 100644
index 000000000000..0bae63c5ca65
--- /dev/null
+++ b/kernel/kcsan/test.c
@@ -0,0 +1,121 @@
+// 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 for the below tests */
+ return prandom_u32() + prandom_u32() != 0;
+}
+
+/*
+ * Test watchpoint encode and decode: check that encoding some access's info,
+ * and then subsequent decode preserves the access's info.
+ */
+static bool test_encode_decode(void)
+{
+ int i;
+
+ for (i = 0; i < ITERS_PER_TEST; ++i) {
+ size_t size = prandom_u32_max(MAX_ENCODABLE_SIZE) + 1;
+ bool is_write = !!prandom_u32_max(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;
+}
+
+/* Test access matching function. */
+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..5dd464e52ab4
--- /dev/null
+++ b/lib/Kconfig.kcsan
@@ -0,0 +1,118 @@
+# 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. See
+ <file:Documentation/dev-tools/kcsan.rst> for more details.
+
+if KCSAN
+
+config KCSAN_DEBUG
+ bool "Debugging of KCSAN internals"
+ default n
+
+config KCSAN_SELFTEST
+ bool "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 "Early enable during boot"
+ default y
+ help
+ If KCSAN should be enabled globally as soon as possible. KCSAN can
+ later be enabled/disabled via debugfs.
+
+config KCSAN_NUM_WATCHPOINTS
+ int "Number of available watchpoints"
+ default 64
+ help
+ Total number of available watchpoints. An address range maps into a
+ specific watchpoint slot as specified in kernel/kcsan/encoding.h.
+ Although larger number of watchpoints may not be usable due to
+ limited number of CPUs, a larger value helps to improve performance
+ due to reducing cache-line contention. The chosen default is a
+ conservative value; we should almost never observe "no_capacity"
+ events (see /sys/kernel/debug/kcsan).
+
+config KCSAN_UDELAY_TASK
+ int "Delay in microseconds (for tasks)"
+ default 80
+ help
+ For tasks, the microsecond delay after setting up a watchpoint.
+
+config KCSAN_UDELAY_INTERRUPT
+ int "Delay in microseconds (for interrupts)"
+ default 20
+ help
+ For interrupts, the microsecond delay after setting up a watchpoint.
+ Interrupts have tighter latency requirements, and their delay should
+ be lower than for tasks.
+
+config KCSAN_DELAY_RANDOMIZE
+ bool "Randomize above delays"
+ default y
+ help
+ If delays should be randomized, where the maximum is KCSAN_UDELAY_*.
+ If false, the chosen delays are always KCSAN_UDELAY_* defined above.
+
+config KCSAN_SKIP_WATCH
+ int "Skip instructions before setting up watchpoint"
+ default 4000
+ help
+ The number of per-CPU memory operations to skip, before another
+ watchpoint is set up, i.e. one in KCSAN_WATCH_SKIP 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_SKIP_WATCH_RANDOMIZE
+ bool "Randomize watchpoint instruction skip count"
+ default y
+ help
+ If instruction skip count should be randomized, where the maximum is
+ KCSAN_WATCH_SKIP. If false, the chosen value is always
+ KCSAN_WATCH_SKIP.
+
+# Note that, while some of the below options could be turned into boot
+# parameters, to optimize for the common use-case, we avoid this because: (a)
+# it would impact performance (and we want to avoid static branch for all
+# {READ,WRITE}_ONCE, atomic_*, bitops, etc.), and (b) complicate the design
+# without real benefit. The main purpose of the below options are for use in
+# fuzzer configs to control reported data races, and are not expected to be
+# switched frequently by a user.
+
+config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
+ bool "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_REPORT_VALUE_CHANGE_ONLY
+ bool "Only report races where watcher observed a data value change"
+ default y
+ help
+ If enabled and a conflicting write is observed via watchpoint, but
+ the data value of the memory location was observed to remain
+ unchanged, do not report the data race.
+
+config KCSAN_IGNORE_ATOMICS
+ bool "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.
+
+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..8952f909f7c9 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -152,6 +152,16 @@ _c_flags += $(if $(patsubst n%,, \
$(CFLAGS_KCOV))
endif

+#
+# Enable KCSAN flags 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),)
--
2.24.0.rc1.363.gb1bccd3e3d-goog
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