On Wed, Oct 16, 2019 at 10:41 AM Marco Elver <elver@xxxxxxxxxx> wrote: > > 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 Do we want to have a different bug title here? Can we also report this as a data-race to simplify report parsing rules? > + > + 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. This part compares KCSAN with KTSAN, do we need it here? I think it might be better to move this to the cover letter as a rationale as to why we went with the watchpoint based approach, instead of the happens-before one. Some performance numbers comparing KCSAN with a non instrumented kernel would be more useful here. > 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 >
