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authorMarco Elver <elver@google.com>2020-02-04 18:21:10 +0100
committerIngo Molnar <mingo@kernel.org>2020-03-21 09:42:18 +0100
commit1e6ee2f0fe8ae682757960edf455e99f611268a0 (patch)
treea7325816ac12d8f67d39f356aad32395e8344175 /kernel/kcsan
parent7ad900d35b49af5a05f595d2274c32e69e01b055 (diff)
kcsan: Add option to assume plain aligned writes up to word size are atomic
This adds option KCSAN_ASSUME_PLAIN_WRITES_ATOMIC. If enabled, plain aligned writes up to word size are assumed to be atomic, and also not subject to other unsafe compiler optimizations resulting in data races. This option has been enabled by default to reflect current kernel-wide preferences. Signed-off-by: Marco Elver <elver@google.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/kcsan')
-rw-r--r--kernel/kcsan/core.c22
1 files changed, 17 insertions, 5 deletions
diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
index 64b30f7716a1..e3c7d8f34f2f 100644
--- a/kernel/kcsan/core.c
+++ b/kernel/kcsan/core.c
@@ -5,6 +5,7 @@
#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>
@@ -169,10 +170,20 @@ static __always_inline struct kcsan_ctx *get_ctx(void)
return in_task() ? &current->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
@@ -193,7 +204,8 @@ static __always_inline bool is_atomic(const volatile void *ptr)
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.
@@ -202,7 +214,7 @@ static __always_inline bool should_watch(const volatile void *ptr, int type)
* 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)
@@ -460,7 +472,7 @@ static __always_inline void check_access(const volatile void *ptr, size_t size,
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);
}