[PATCH] kasan: test: Silence allocation warnings from GCC 12

[Kees Cook]

GCC 12 is able to see more problems with allocation sizes at compile
time, so these must be silenced so the runtime checks will still be
available. Use OPTIMIZER_HIDE_VAR() to silence the new warnings:

lib/test_kasan.c: In function 'ksize_uaf':
lib/test_kasan.c:781:61: warning: array subscript 120 is outside array bounds of 'void[120]' [-Warray-bounds]
  781 |         KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[size]);
      |                                       ~~~~~~~~~~~~~~~~~~~~~~^~~~~~
lib/test_kasan.c:96:9: note: in definition of macro 'KUNIT_EXPECT_KASAN_FAIL'
   96 |         expression;                                                     \
      |         ^~~~~~~~~~
In function 'kmalloc',
    inlined from 'ksize_uaf' at lib/test_kasan.c:775:8:
./include/linux/slab.h:581:24: note: at offset 120 into object of size 120 allocated by 'kmem_cache_alloc_trace'
  581 |                 return kmem_cache_alloc_trace(
      |                        ^~~~~~~~~~~~~~~~~~~~~~~
  582 |                                 kmalloc_caches[kmalloc_type(flags)][index],
      |                                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  583 |                                 flags, size);
      |                                 ~~~~~~~~~~~~

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 | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 26a5c9007653..a19b3d608e3e 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -124,6 +124,7 @@ static void kmalloc_oob_right(struct kunit *test)
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
+	OPTIMIZER_HIDE_VAR(ptr);
 
 	/*
 	 * An unaligned access past the requested kmalloc size.
@@ -185,6 +186,7 @@ static void kmalloc_pagealloc_oob_right(struct kunit *test)
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
+	OPTIMIZER_HIDE_VAR(ptr);
 	KUNIT_EXPECT_KASAN_FAIL(test, ptr[size + OOB_TAG_OFF] = 0);
 
 	kfree(ptr);
@@ -265,6 +267,7 @@ static void kmalloc_large_oob_right(struct kunit *test)
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
 
+	OPTIMIZER_HIDE_VAR(ptr);
 	KUNIT_EXPECT_KASAN_FAIL(test, ptr[size] = 0);
 	kfree(ptr);
 }
@@ -748,6 +751,7 @@ static void ksize_unpoisons_memory(struct kunit *test)
 
 	ptr = kmalloc(size, GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
+	OPTIMIZER_HIDE_VAR(ptr);
 	real_size = ksize(ptr);
 
 	/* This access shouldn't trigger a KASAN report. */
-- 
2.30.2