mm: kmsan: implement kmsan_memmove()

Provide a hook that can be used by custom memcpy implementations to tell
KMSAN that the metadata needs to be copied.  Without that, false positive
reports are possible in the cases where KMSAN fails to intercept memory
initialization.

Link: https://lore.kernel.org/all/[email protected]/
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Alexander Potapenko <[email protected]>
Suggested-by: Tetsuo Handa <[email protected]>
Reviewed-by: Marco Elver <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Tetsuo Handa <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

2 files changed, 26 insertions, 0 deletions

diff --git a/include/linux/kmsan-checks.h b/include/linux/kmsan-checks.h
index c4cae333deec..e1082dc40abc 100644
--- a/include/linux/kmsan-checks.h
+++ b/include/linux/kmsan-checks.h
@@ -61,6 +61,17 @@ void kmsan_check_memory(const void *address, size_t size);
 void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy,
 			size_t left);
 
+/**
+ * kmsan_memmove() - Notify KMSAN about a data copy within kernel.
+ * @to:   destination address in the kernel.
+ * @from: source address in the kernel.
+ * @size: number of bytes to copy.
+ *
+ * Invoked after non-instrumented version (e.g. implemented using assembly
+ * code) of memmove()/memcpy() is called, in order to copy KMSAN's metadata.
+ */
+void kmsan_memmove(void *to, const void *from, size_t to_copy);
+
 #else
 
 static inline void kmsan_poison_memory(const void *address, size_t size,
@@ -78,6 +89,10 @@ static inline void kmsan_copy_to_user(void __user *to, const void *from,
 {
 }
 
+static inline void kmsan_memmove(void *to, const void *from, size_t to_copy)
+{
+}
+
 #endif
 
 #endif /* _LINUX_KMSAN_CHECKS_H */
diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
index 0b09daa188ef..22e8657800ef 100644
--- a/mm/kmsan/hooks.c
+++ b/mm/kmsan/hooks.c
@@ -285,6 +285,17 @@ void kmsan_copy_to_user(void __user *to, const void *from, size_t to_copy,
 }
 EXPORT_SYMBOL(kmsan_copy_to_user);
 
+void kmsan_memmove(void *to, const void *from, size_t size)
+{
+	if (!kmsan_enabled || kmsan_in_runtime())
+		return;
+
+	kmsan_enter_runtime();
+	kmsan_internal_memmove_metadata(to, (void *)from, size);
+	kmsan_leave_runtime();
+}
+EXPORT_SYMBOL(kmsan_memmove);
+
 /* Helper function to check an URB. */
 void kmsan_handle_urb(const struct urb *urb, bool is_out)
 {