Re: [PATCH] kasan: test: Silence GCC 12 warnings

[Marco Elver]

On Wed, 8 Jun 2022 at 23:40, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> GCC 12 continues to get smarter about array accesses. The KASAN tests
> are expecting to explicitly test out-of-bounds conditions at run-time,
> so hide the variable from GCC, to avoid warnings like:
>
> ../lib/test_kasan.c: In function 'ksize_uaf':
> ../lib/test_kasan.c:790:61: warning: array subscript 120 is outside array bounds of 'void[120]' [-Warray-bounds]

Since this keeps happening, I wonder if we could just pass
'-Wno-array-bounds' ? We already have 'CFLAGS_test_kasan.o += $(call
cc-disable-warning, vla)'.

Although eventually I'd assume all the OPTIMIZE_HIDE_VAR() should be
in place, and hopefully it'll have been the last one. I leave it to
you.

>   790 |         KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[size]);
>       |                                       ~~~~~~~~~~~~~~~~~~~~~~^~~~~~
> ../lib/test_kasan.c:97:9: note: in definition of macro 'KUNIT_EXPECT_KASAN_FAIL'
>    97 |         expression; \
>       |         ^~~~~~~~~~
>
> Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
> Cc: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
> Cc: kasan-dev@xxxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
>  lib/test_kasan.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index c233b1a4e984..58c1b01ccfe2 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -131,6 +131,7 @@ 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.
>          * Only generic KASAN can precisely detect these.
> @@ -159,6 +160,7 @@ static void kmalloc_oob_left(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 = *(ptr - 1));
>         kfree(ptr);
>  }
> @@ -171,6 +173,7 @@ static void kmalloc_node_oob_right(struct kunit *test)
>         ptr = kmalloc_node(size, GFP_KERNEL, 0);
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> +       OPTIMIZER_HIDE_VAR(ptr);
>         KUNIT_EXPECT_KASAN_FAIL(test, ptr[0] = ptr[size]);
>         kfree(ptr);
>  }
> @@ -191,6 +194,7 @@ 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);
> @@ -271,6 +275,7 @@ 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);
>  }
> @@ -410,6 +415,8 @@ static void kmalloc_oob_16(struct kunit *test)
>         ptr2 = kmalloc(sizeof(*ptr2), GFP_KERNEL);
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr2);
>
> +       OPTIMIZER_HIDE_VAR(ptr1);
> +       OPTIMIZER_HIDE_VAR(ptr2);
>         KUNIT_EXPECT_KASAN_FAIL(test, *ptr1 = *ptr2);
>         kfree(ptr1);
>         kfree(ptr2);
> @@ -756,6 +763,8 @@ static void ksize_unpoisons_memory(struct kunit *test)
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>         real_size = ksize(ptr);
>
> +       OPTIMIZER_HIDE_VAR(ptr);
> +
>         /* This access shouldn't trigger a KASAN report. */
>         ptr[size] = 'x';
>
> @@ -778,6 +787,7 @@ static void ksize_uaf(struct kunit *test)
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>         kfree(ptr);
>
> +       OPTIMIZER_HIDE_VAR(ptr);
>         KUNIT_EXPECT_KASAN_FAIL(test, ksize(ptr));
>         KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[0]);
>         KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[size]);
> --
> 2.32.0
>
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