lib/test_kasan.c: fix KASAN unit tests for tag-based KASAN

We use tag-based KASAN, then KASAN unit tests don't detect out-of-bounds
memory access. They need to be fixed.

With tag-based KASAN, the state of each 16 aligned bytes of memory is
encoded in one shadow byte and the shadow value is tag of pointer, so
we need to read next shadow byte, the shadow value is not equal to tag
value of pointer, so that tag-based KASAN will detect out-of-bounds
memory access.

[walter-zh.wu@mediatek.com: use KASAN_SHADOW_SCALE_SIZE instead of 13]
  Link: http://lkml.kernel.org/r/20200708132524.11688-1-walter-zh.wu@mediatek.com

Suggested-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Matthias Brugger <matthias.bgg@gmail.com>
Link: http://lkml.kernel.org/r/20200706115039.16750-1-walter-zh.wu@mediatek.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/test_kasan.c

@@ -23,6 +23,10 @@
 
 #include <asm/page.h>
 
+#include "../mm/kasan/kasan.h"
+
+#define OOB_TAG_OFF (IS_ENABLED(CONFIG_KASAN_GENERIC) ? 0 : KASAN_SHADOW_SCALE_SIZE)
+
 /*
  * We assign some test results to these globals to make sure the tests
  * are not eliminated as dead code.
@@ -48,7 +52,8 @@ static noinline void __init kmalloc_oob_right(void)
 		return;
 	}
 
-	ptr[size] = 'x';
+	ptr[size + OOB_TAG_OFF] = 'x';
+
 	kfree(ptr);
 }
 
@@ -100,7 +105,8 @@ static noinline void __init kmalloc_pagealloc_oob_right(void)
 		return;
 	}
 
-	ptr[size] = 0;
+	ptr[size + OOB_TAG_OFF] = 0;
+
 	kfree(ptr);
 }
 
@@ -170,7 +176,8 @@ static noinline void __init kmalloc_oob_krealloc_more(void)
 		return;
 	}
 
-	ptr2[size2] = 'x';
+	ptr2[size2 + OOB_TAG_OFF] = 'x';
+
 	kfree(ptr2);
 }
 
@@ -188,7 +195,9 @@ static noinline void __init kmalloc_oob_krealloc_less(void)
 		kfree(ptr1);
 		return;
 	}
-	ptr2[size2] = 'x';
+
+	ptr2[size2 + OOB_TAG_OFF] = 'x';
+
 	kfree(ptr2);
 }
 
@@ -224,7 +233,8 @@ static noinline void __init kmalloc_oob_memset_2(void)
 		return;
 	}
 
-	memset(ptr+7, 0, 2);
+	memset(ptr + 7 + OOB_TAG_OFF, 0, 2);
+
 	kfree(ptr);
 }
 
@@ -240,7 +250,8 @@ static noinline void __init kmalloc_oob_memset_4(void)
 		return;
 	}
 
-	memset(ptr+5, 0, 4);
+	memset(ptr + 5 + OOB_TAG_OFF, 0, 4);
+
 	kfree(ptr);
 }
 
@@ -257,7 +268,8 @@ static noinline void __init kmalloc_oob_memset_8(void)
 		return;
 	}
 
-	memset(ptr+1, 0, 8);
+	memset(ptr + 1 + OOB_TAG_OFF, 0, 8);
+
 	kfree(ptr);
 }
 
@@ -273,7 +285,8 @@ static noinline void __init kmalloc_oob_memset_16(void)
 		return;
 	}
 
-	memset(ptr+1, 0, 16);
+	memset(ptr + 1 + OOB_TAG_OFF, 0, 16);
+
 	kfree(ptr);
 }
 
@@ -289,7 +302,8 @@ static noinline void __init kmalloc_oob_in_memset(void)
 		return;
 	}
 
-	memset(ptr, 0, size+5);
+	memset(ptr, 0, size + 5 + OOB_TAG_OFF);
+
 	kfree(ptr);
 }
 
@@ -423,7 +437,8 @@ static noinline void __init kmem_cache_oob(void)
 		return;
 	}
 
-	*p = p[size];
+	*p = p[size + OOB_TAG_OFF];
+
 	kmem_cache_free(cache, p);
 	kmem_cache_destroy(cache);
 }
@@ -520,25 +535,25 @@ static noinline void __init copy_user_test(void)
 	}
 
 	pr_info("out-of-bounds in copy_from_user()\n");
-	unused = copy_from_user(kmem, usermem, size + 1);
+	unused = copy_from_user(kmem, usermem, size + 1 + OOB_TAG_OFF);
 
 	pr_info("out-of-bounds in copy_to_user()\n");
-	unused = copy_to_user(usermem, kmem, size + 1);
+	unused = copy_to_user(usermem, kmem, size + 1 + OOB_TAG_OFF);
 
 	pr_info("out-of-bounds in __copy_from_user()\n");
-	unused = __copy_from_user(kmem, usermem, size + 1);
+	unused = __copy_from_user(kmem, usermem, size + 1 + OOB_TAG_OFF);
 
 	pr_info("out-of-bounds in __copy_to_user()\n");
-	unused = __copy_to_user(usermem, kmem, size + 1);
+	unused = __copy_to_user(usermem, kmem, size + 1 + OOB_TAG_OFF);
 
 	pr_info("out-of-bounds in __copy_from_user_inatomic()\n");
-	unused = __copy_from_user_inatomic(kmem, usermem, size + 1);
+	unused = __copy_from_user_inatomic(kmem, usermem, size + 1 + OOB_TAG_OFF);
 
 	pr_info("out-of-bounds in __copy_to_user_inatomic()\n");
-	unused = __copy_to_user_inatomic(usermem, kmem, size + 1);
+	unused = __copy_to_user_inatomic(usermem, kmem, size + 1 + OOB_TAG_OFF);
 
 	pr_info("out-of-bounds in strncpy_from_user()\n");
-	unused = strncpy_from_user(kmem, usermem, size + 1);
+	unused = strncpy_from_user(kmem, usermem, size + 1 + OOB_TAG_OFF);
 
 	vm_munmap((unsigned long)usermem, PAGE_SIZE);
 	kfree(kmem);