[PATCH v2 2/3] instrumented.h: add instrument_memcpy_before, instrument_memcpy_after

[Alexander Potapenko]

Bug detection tools based on compiler instrumentation may miss memory
accesses in custom memcpy implementations (such as copy_mc_to_kernel).
Provide instrumentation hooks that tell KASAN, KCSAN, and KMSAN about
such accesses.

Link: https://lore.kernel.org/all/3b7dbd88-0861-4638-b2d2-911c97a4cadf@xxxxxxxxxxxxxxxxxxx/
Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>

---
 v2: fix a copypasto in a comment spotted by Linus
---
 include/linux/instrumented.h | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/include/linux/instrumented.h b/include/linux/instrumented.h
index 1b608e00290aa..711a1f0d1a735 100644
--- a/include/linux/instrumented.h
+++ b/include/linux/instrumented.h
@@ -147,6 +147,41 @@ instrument_copy_from_user_after(const void *to, const void __user *from,
 	kmsan_unpoison_memory(to, n - left);
 }
 
+/**
+ * instrument_memcpy_before - add instrumentation before non-instrumented memcpy
+ * @to: destination address
+ * @from: source address
+ * @n: number of bytes to copy
+ *
+ * Instrument memory accesses that happen in custom memcpy implementations. The
+ * instrumentation should be inserted before the memcpy call.
+ */
+static __always_inline void instrument_memcpy_before(void *to, const void *from,
+						     unsigned long n)
+{
+	kasan_check_write(to, n);
+	kasan_check_read(from, n);
+	kcsan_check_write(to, n);
+	kcsan_check_read(from, n);
+}
+
+/**
+ * instrument_memcpy_after - add instrumentation after non-instrumented memcpy
+ * @to: destination address
+ * @from: source address
+ * @n: number of bytes to copy
+ * @left: number of bytes not copied (if known)
+ *
+ * Instrument memory accesses that happen in custom memcpy implementations. The
+ * instrumentation should be inserted after the memcpy call.
+ */
+static __always_inline void instrument_memcpy_after(void *to, const void *from,
+						    unsigned long n,
+						    unsigned long left)
+{
+	kmsan_memmove(to, from, n - left);
+}
+
 /**
  * instrument_get_user() - add instrumentation to get_user()-like macros
  * @to: destination variable, may not be address-taken
-- 
2.44.0.291.gc1ea87d7ee-goog