#include <linux/delay.h>
#include <linux/export.h>
#include <linux/init.h>
+#include <linux/kernel.h>
#include <linux/percpu.h>
#include <linux/preempt.h>
#include <linux/random.h>
return in_task() ? ¤t->kcsan_ctx : raw_cpu_ptr(&kcsan_cpu_ctx);
}
-static __always_inline bool is_atomic(const volatile void *ptr)
+static __always_inline bool
+is_atomic(const volatile void *ptr, size_t size, int type)
{
- struct kcsan_ctx *ctx = get_ctx();
+ struct kcsan_ctx *ctx;
+
+ if ((type & KCSAN_ACCESS_ATOMIC) != 0)
+ return true;
+ if (IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC) &&
+ (type & KCSAN_ACCESS_WRITE) != 0 && size <= sizeof(long) &&
+ IS_ALIGNED((unsigned long)ptr, size))
+ return true; /* Assume aligned writes up to word size are atomic. */
+
+ ctx = get_ctx();
if (unlikely(ctx->atomic_next > 0)) {
/*
* Because we do not have separate contexts for nested
return kcsan_is_atomic(ptr);
}
-static __always_inline bool should_watch(const volatile void *ptr, int type)
+static __always_inline bool
+should_watch(const volatile void *ptr, size_t size, int type)
{
/*
* Never set up watchpoints when memory operations are atomic.
* 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))
+ if (is_atomic(ptr, size, type))
return false;
if (this_cpu_dec_return(kcsan_skip) >= 0)
if (unlikely(watchpoint != NULL))
kcsan_found_watchpoint(ptr, size, type, watchpoint,
encoded_watchpoint);
- else if (unlikely(should_watch(ptr, type)))
+ else if (unlikely(should_watch(ptr, size, type)))
kcsan_setup_watchpoint(ptr, size, type);
}
limiting reporting to avoid flooding the console with reports.
Setting this to 0 disables rate limiting.
-# 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 is for use in
-# fuzzer configs to control reported data races, and they are not expected
-# to be switched frequently by a user.
+# The main purpose of the below options is to control reported data races (e.g.
+# in fuzzer configs), and are not expected to be switched frequently by other
+# users. We could turn some of them into boot parameters, but given they should
+# not be switched normally, let's keep them here to simplify configuration.
+#
+# The defaults below are chosen to be very conservative, and may miss certain
+# bugs.
config KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
bool "Report races of unknown origin"
the data value of the memory location was observed to remain
unchanged, do not report the data race.
+config KCSAN_ASSUME_PLAIN_WRITES_ATOMIC
+ bool "Assume that plain aligned writes up to word size are atomic"
+ default y
+ help
+ Assume that plain aligned writes up to word size are atomic by
+ default, and also not subject to other unsafe compiler optimizations
+ resulting in data races. This will cause KCSAN to not report data
+ races due to conflicts where the only plain accesses are aligned
+ writes up to word size: conflicts between marked reads and plain
+ aligned writes up to word size will not be reported as data races;
+ notice that data races between two conflicting plain aligned writes
+ will also not be reported.
+
config KCSAN_IGNORE_ATOMICS
bool "Do not instrument marked atomic accesses"
help