On Mon, Sep 12, 2022 at 11:45:40AM +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+ Signed-off-by: Marco Elver elver@google.com

Queued and pushed, thank you!

Thanx, Paul

---

v3:

• Truncate sizes larger than MAX_ENCODABLE_SIZE, so we still set up watchpoints on them. Iterating through MAX_ENCODABLE_SIZE blocks may result in pathological cases where performance would seriously suffer. So let's avoid that for now.
• Just use memcpy/memset/memmove instead of __mem*() functions. Many architectures that already support KCSAN don't define them (mips, s390), and having both __mem* and mem versions of the functions provides little benefit elsewhere; and backporting would become more difficult, too. The compiler should not inline them given all parameters are non-constants here.

v2:

• Fix for architectures which do not provide their own memcpy/memset/memmove and instead use the generic versions in lib/string. In this case we'll just alias the __tsan_ variants.

---

kernel/kcsan/core.c | 50 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 50 insertions(+)

diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c index fe12dfe254ec..54d077e1a2dc 100644 --- a/kernel/kcsan/core.c +++ b/kernel/kcsan/core.c @@ -14,10 +14,12 @@ #include <linux/init.h> #include <linux/kernel.h> #include <linux/list.h> +#include <linux/minmax.h> #include <linux/moduleparam.h> #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 +1310,51 @@ noinline void __tsan_atomic_signal_fence(int memorder) } } EXPORT_SYMBOL(__tsan_atomic_signal_fence);

+#ifdef __HAVE_ARCH_MEMSET +void *__tsan_memset(void *s, int c, size_t count); +noinline void *__tsan_memset(void *s, int c, size_t count) +{

• /*

• * Instead of not setting up watchpoints where accessed size is greater
  

• * than MAX_ENCODABLE_SIZE, truncate checked size to MAX_ENCODABLE_SIZE.
  

• */
  

• size_t check_len = min_t(size_t, count, MAX_ENCODABLE_SIZE);
• check_access(s, check_len, KCSAN_ACCESS_WRITE, _RET_IP_);
• return memset(s, c, count);

+} +#else +void *__tsan_memset(void *s, int c, size_t count) __alias(memset); +#endif +EXPORT_SYMBOL(__tsan_memset);

+#ifdef __HAVE_ARCH_MEMMOVE +void *__tsan_memmove(void *dst, const void *src, size_t len); +noinline void *__tsan_memmove(void *dst, const void *src, size_t len) +{

• size_t check_len = min_t(size_t, len, MAX_ENCODABLE_SIZE);
• check_access(dst, check_len, KCSAN_ACCESS_WRITE, _RET_IP_);
• check_access(src, check_len, 0, _RET_IP_);
• return memmove(dst, src, len);

+} +#else +void *__tsan_memmove(void *dst, const void *src, size_t len) __alias(memmove); +#endif +EXPORT_SYMBOL(__tsan_memmove);

+#ifdef __HAVE_ARCH_MEMCPY +void *__tsan_memcpy(void *dst, const void *src, size_t len); +noinline void *__tsan_memcpy(void *dst, const void *src, size_t len) +{

• size_t check_len = min_t(size_t, len, MAX_ENCODABLE_SIZE);
• check_access(dst, check_len, KCSAN_ACCESS_WRITE, _RET_IP_);
• check_access(src, check_len, 0, _RET_IP_);
• return memcpy(dst, src, len);

+} +#else +void *__tsan_memcpy(void *dst, const void *src, size_t len) __alias(memcpy); +#endif

+EXPORT_SYMBOL(__tsan_memcpy);

2.37.2.789.g6183377224-goog