[patch 11/15] kasan: test: silence intentional read overflow warnings

[Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>]

From: Kees Cook <keescook@xxxxxxxxxxxx>
Subject: kasan: test: silence intentional read overflow warnings

As done in commit d73dad4eb5ad ("kasan: test: bypass __alloc_size checks")
for __write_overflow warnings, also silence some more cases that trip the
__read_overflow warnings seen in 5.16-rc1[1]:

In file included from /kisskb/src/include/linux/string.h:253,
                 from /kisskb/src/include/linux/bitmap.h:10,
                 from /kisskb/src/include/linux/cpumask.h:12,
                 from /kisskb/src/include/linux/mm_types_task.h:14,
                 from /kisskb/src/include/linux/mm_types.h:5,
                 from /kisskb/src/include/linux/page-flags.h:13,
                 from /kisskb/src/arch/arm64/include/asm/mte.h:14,
                 from /kisskb/src/arch/arm64/include/asm/pgtable.h:12,
                 from /kisskb/src/include/linux/pgtable.h:6,
                 from /kisskb/src/include/linux/kasan.h:29,
                 from /kisskb/src/lib/test_kasan.c:10:
In function 'memcmp',
    inlined from 'kasan_memcmp' at /kisskb/src/lib/test_kasan.c:897:2:
/kisskb/src/include/linux/fortify-string.h:263:25: error: call to '__read_overflow' declared with attribute error: detected read beyond size of object (1st parameter)
  263 |                         __read_overflow();
      |                         ^~~~~~~~~~~~~~~~~
In function 'memchr',
    inlined from 'kasan_memchr' at /kisskb/src/lib/test_kasan.c:872:2:
/kisskb/src/include/linux/fortify-string.h:277:17: error: call to '__read_overflow' declared with attribute error: detected read beyond size of object (1st parameter)
  277 |                 __read_overflow();
      |                 ^~~~~~~~~~~~~~~~~

[1] http://kisskb.ellerman.id.au/kisskb/buildresult/14660585/log/

Link: https://lkml.kernel.org/r/20211116004111.3171781-1-keescook@xxxxxxxxxxxx
Fixes: d73dad4eb5ad ("kasan: test: bypass __alloc_size checks")
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Acked-by: Marco Elver <elver@xxxxxxxxxx>
Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 lib/test_kasan.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/lib/test_kasan.c~kasan-test-silence-intentional-read-overflow-warnings
+++ a/lib/test_kasan.c
@@ -869,6 +869,7 @@ static void kasan_memchr(struct kunit *t
 	ptr = kmalloc(size, GFP_KERNEL | __GFP_ZERO);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
+	OPTIMIZER_HIDE_VAR(size);
 	KUNIT_EXPECT_KASAN_FAIL(test,
 		kasan_ptr_result = memchr(ptr, '1', size + 1));
 
@@ -894,6 +895,7 @@ static void kasan_memcmp(struct kunit *t
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 	memset(arr, 0, sizeof(arr));
 
+	OPTIMIZER_HIDE_VAR(size);
 	KUNIT_EXPECT_KASAN_FAIL(test,
 		kasan_int_result = memcmp(ptr, arr, size+1));
 	kfree(ptr);
_