[PATCH] kasan: test: Bypass __alloc_size checks

[Kees Cook]

Intentional overflows, as performed by the KASAN tests, are detected
at compile time[1] (instead of only at run-time) with the addition of
__alloc_size. Fix this by forcing the compiler into not being able to
trust the size used following the kmalloc()s.

[1] https://lore.kernel.org/lkml/20211005184717.65c6d8eb39350395e387b71f@xxxxxxxxxxxxxxxxxxxx

Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: kasan-dev@xxxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 lib/test_kasan.c        | 10 +++++-----
 lib/test_kasan_module.c |  2 +-
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 8835e0784578..0e1f8d5281b4 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -435,7 +435,7 @@ static void kmalloc_uaf_16(struct kunit *test)
 static void kmalloc_oob_memset_2(struct kunit *test)
 {
 	char *ptr;
-	size_t size = 128 - KASAN_GRANULE_SIZE;
+	volatile size_t size = 128 - KASAN_GRANULE_SIZE;
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
@@ -447,7 +447,7 @@ static void kmalloc_oob_memset_2(struct kunit *test)
 static void kmalloc_oob_memset_4(struct kunit *test)
 {
 	char *ptr;
-	size_t size = 128 - KASAN_GRANULE_SIZE;
+	volatile size_t size = 128 - KASAN_GRANULE_SIZE;
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
@@ -459,7 +459,7 @@ static void kmalloc_oob_memset_4(struct kunit *test)
 static void kmalloc_oob_memset_8(struct kunit *test)
 {
 	char *ptr;
-	size_t size = 128 - KASAN_GRANULE_SIZE;
+	volatile size_t size = 128 - KASAN_GRANULE_SIZE;
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
@@ -471,7 +471,7 @@ static void kmalloc_oob_memset_8(struct kunit *test)
 static void kmalloc_oob_memset_16(struct kunit *test)
 {
 	char *ptr;
-	size_t size = 128 - KASAN_GRANULE_SIZE;
+	volatile size_t size = 128 - KASAN_GRANULE_SIZE;
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
@@ -483,7 +483,7 @@ static void kmalloc_oob_memset_16(struct kunit *test)
 static void kmalloc_oob_in_memset(struct kunit *test)
 {
 	char *ptr;
-	size_t size = 128 - KASAN_GRANULE_SIZE;
+	volatile size_t size = 128 - KASAN_GRANULE_SIZE;
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
diff --git a/lib/test_kasan_module.c b/lib/test_kasan_module.c
index 7ebf433edef3..c8cc77b1dcf3 100644
--- a/lib/test_kasan_module.c
+++ b/lib/test_kasan_module.c
@@ -19,7 +19,7 @@ static noinline void __init copy_user_test(void)
 {
 	char *kmem;
 	char __user *usermem;
-	size_t size = 128 - KASAN_GRANULE_SIZE;
+	volatile size_t size = 128 - KASAN_GRANULE_SIZE;
 	int __maybe_unused unused;
 
 	kmem = kmalloc(size, GFP_KERNEL);
-- 
2.30.2