On Wed, Sep 07, 2022 at 07:39:02PM +0200, Marco Elver wrote:
With Clang version 16+, -fsanitize=thread will turn memcpy/memset/memmove calls in instrumented functions into __tsan_memcpy/__tsan_memset/__tsan_memmove calls respectively.
Add these functions to the core KCSAN runtime, so that we (a) catch data races with mem* functions, and (b) won't run into linker errors with such newer compilers.
Cc: stable@vger.kernel.org # v5.10+
For (b) I think this is Ok, but for (a), what the atomic guarantee of our mem* functions? Per-byte atomic or something more complicated (for example, providing best effort atomic if a memory location in the range is naturally-aligned to a machine word)?
If it's a per-byte atomicity, then maybe another KCSAN_ACCESS_* flags is needed, otherwise memset(0x8, 0, 0x2) is considered as atomic if ASSUME_PLAIN_WRITES_ATOMIC=y. Unless I'm missing something.
Anyway, this may be worth another patch and some discussion/doc, because it just improve the accuracy of the tool. In other words, this patch and the "stable" tag look good to me.
Regards, Boqun
Signed-off-by: Marco Elver elver@google.com
kernel/kcsan/core.c | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+)
diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c index fe12dfe254ec..66ef48aa86e0 100644 --- a/kernel/kcsan/core.c +++ b/kernel/kcsan/core.c @@ -18,6 +18,7 @@ #include <linux/percpu.h> #include <linux/preempt.h> #include <linux/sched.h> +#include <linux/string.h> #include <linux/uaccess.h> #include "encoding.h" @@ -1308,3 +1309,29 @@ noinline void __tsan_atomic_signal_fence(int memorder) } } EXPORT_SYMBOL(__tsan_atomic_signal_fence);
+void *__tsan_memset(void *s, int c, size_t count); +noinline void *__tsan_memset(void *s, int c, size_t count) +{
- check_access(s, count, KCSAN_ACCESS_WRITE, _RET_IP_);
- return __memset(s, c, count);
+} +EXPORT_SYMBOL(__tsan_memset);
+void *__tsan_memmove(void *dst, const void *src, size_t len); +noinline void *__tsan_memmove(void *dst, const void *src, size_t len) +{
- check_access(dst, len, KCSAN_ACCESS_WRITE, _RET_IP_);
- check_access(src, len, 0, _RET_IP_);
- return __memmove(dst, src, len);
+} +EXPORT_SYMBOL(__tsan_memmove);
+void *__tsan_memcpy(void *dst, const void *src, size_t len); +noinline void *__tsan_memcpy(void *dst, const void *src, size_t len) +{
- check_access(dst, len, KCSAN_ACCESS_WRITE, _RET_IP_);
- check_access(src, len, 0, _RET_IP_);
- return __memcpy(dst, src, len);
+}
+EXPORT_SYMBOL(__tsan_memcpy);
2.37.2.789.g6183377224-goog