kasan: add test for invalid size in memmove

Test negative size in memmove in order to verify whether it correctly get
KASAN report.

Casting negative numbers to size_t would indeed turn up as a large size_t,
so it will have out-of-bounds bug and be detected by KASAN.

[walter-zh.wu@mediatek.com: fix -Wstringop-overflow warning]
  Link: http://lkml.kernel.org/r/20200311134244.13016-1-walter-zh.wu@mediatek.comSigned-off-by: Walter Wu <walter-zh.wu@mediatek.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: kernel test robot <lkp@intel.com>
Link: http://lkml.kernel.org/r/20191112065313.7060-1-walter-zh.wu@mediatek.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/test_kasan.c

@@ -285,6 +285,24 @@ static noinline void __init kmalloc_oob_in_memset(void)
 	kfree(ptr);
 }
 
+static noinline void __init kmalloc_memmove_invalid_size(void)
+{
+	char *ptr;
+	size_t size = 64;
+	volatile size_t invalid_size = -2;
+
+	pr_info("invalid size in memmove\n");
+	ptr = kmalloc(size, GFP_KERNEL);
+	if (!ptr) {
+		pr_err("Allocation failed\n");
+		return;
+	}
+
+	memset((char *)ptr, 0, 64);
+	memmove((char *)ptr, (char *)ptr + 4, invalid_size);
+	kfree(ptr);
+}
+
 static noinline void __init kmalloc_uaf(void)
 {
 	char *ptr;
@@ -799,6 +817,7 @@ static int __init kmalloc_tests_init(void)
 	kmalloc_oob_memset_4();
 	kmalloc_oob_memset_8();
 	kmalloc_oob_memset_16();
+	kmalloc_memmove_invalid_size();
 	kmalloc_uaf();
 	kmalloc_uaf_memset();
 	kmalloc_uaf2();