[PATCH v3] x86: disable non-instrumented version of copy_page when KMSAN is enabled

[Tetsuo Handa]

Commit afb2d666d025 ("zsmalloc: use copy_page for full page copy") caused
a false-positive KMSAN warning. Implement copy_page() using memcpy() when
KMSAN is enabled.

  BUG: KMSAN: use-after-free in obj_malloc+0x6cc/0x7b0
  Uninit was stored to memory at:
   obj_malloc+0x70a/0x7b0
  Uninit was created at:
   free_unref_page_prepare+0x130/0xfc0

Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
Changes in v3:
  Update description/comment and use include file, suggested by
  Thomas Gleixner.
  
 arch/x86/include/asm/page_64.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
index cc6b8e087192..98a71727dbac 100644
--- a/arch/x86/include/asm/page_64.h
+++ b/arch/x86/include/asm/page_64.h
@@ -9,6 +9,7 @@
 #include <asm/alternative.h>
 
 #include <linux/kmsan-checks.h>
+#include <linux/string.h>
 
 /* duplicated to the one in bootmem.h */
 extern unsigned long max_pfn;
@@ -58,7 +59,18 @@ static inline void clear_page(void *page)
 			   : "cc", "memory", "rax", "rcx");
 }
 
+#ifdef CONFIG_KMSAN
+/*
+ * The assembly version of copy_page() is not instrumented and
+ * therefore breaks KMSAN. Fall back to memcpy.
+ */
+static inline void copy_page(void *to, void *from)
+{
+	memcpy(to, from, PAGE_SIZE);
+}
+#else
 void copy_page(void *to, void *from);
+#endif
 
 #ifdef CONFIG_X86_5LEVEL
 /*
-- 
2.34.1