From: Andrey Konovalov <andreyknvl@google.com>

GCC's -Warray-bounds option detects out-of-bounds accesses to
statically-sized allocations in krealloc out-of-bounds tests.

Use OPTIMIZER_HIDE_VAR to suppress the warning.

Also change kmalloc_memmove_invalid_size to use OPTIMIZER_HIDE_VAR
instead of a volatile variable.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

---

Changes v2->v3:
- Add comment for added -Warray-bounds-related OPTIMIZER_HIDE_VAR.

Changes v1->v2:
- Hide ptr2 instead of size1 and size2 to be consistent with other
  uses of OPTIMIZER_HIDE_VAR in KASAN tests.
---
 mm/kasan/kasan_test.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/kasan/kasan_test.c b/mm/kasan/kasan_test.c
index 71cb402c404f..f50b11d84f41 100644
--- a/mm/kasan/kasan_test.c
+++ b/mm/kasan/kasan_test.c
@@ -333,6 +333,9 @@ static void krealloc_more_oob_helper(struct kunit *test,
 	ptr2 = krealloc(ptr1, size2, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr2);
 
+	/* Suppress -Warray-bounds warnings. */
+	OPTIMIZER_HIDE_VAR(ptr2);
+
 	/* All offsets up to size2 must be accessible. */
 	ptr2[size1 - 1] = 'x';
 	ptr2[size1] = 'x';
@@ -365,6 +368,9 @@ static void krealloc_less_oob_helper(struct kunit *test,
 	ptr2 = krealloc(ptr1, size2, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr2);
 
+	/* Suppress -Warray-bounds warnings. */
+	OPTIMIZER_HIDE_VAR(ptr2);
+
 	/* Must be accessible for all modes. */
 	ptr2[size2 - 1] = 'x';
 
@@ -578,13 +584,14 @@ static void kmalloc_memmove_invalid_size(struct kunit *test)
 {
 	char *ptr;
 	size_t size = 64;
-	volatile size_t invalid_size = size;
+	size_t invalid_size = size;
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
 	memset((char *)ptr, 0, 64);
 	OPTIMIZER_HIDE_VAR(ptr);
+	OPTIMIZER_HIDE_VAR(invalid_size);
 	KUNIT_EXPECT_KASAN_FAIL(test,
 		memmove((char *)ptr, (char *)ptr + 4, invalid_size));
 	kfree(ptr);
-- 
2.25.1

On Mon, Sep 26, 2022 at 08:08:47PM +0200, andrey.konovalov@linux.dev wrote:
> From: Andrey Konovalov <andreyknvl@google.com>
> 
> GCC's -Warray-bounds option detects out-of-bounds accesses to
> statically-sized allocations in krealloc out-of-bounds tests.
> 
> Use OPTIMIZER_HIDE_VAR to suppress the warning.
> 
> Also change kmalloc_memmove_invalid_size to use OPTIMIZER_HIDE_VAR
> instead of a volatile variable.
> 
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook