Re: [PATCH] kunit: kasan_test: disable fortify string checker on kmalloc_oob_memset

[Andrey Konovalov]

On Wed, Dec 13, 2023 at 12:27 AM Nico Pache <npache@xxxxxxxxxx> wrote:
>
> similar to commit 09c6304e38e4 ("kasan: test: fix compatibility with
> FORTIFY_SOURCE") the kernel is panicing in kmalloc_oob_memset_*.
>
> This is due to the `ptr` not being hidden from the optimizer which would
> disable the runtime fortify string checker.
>
> kernel BUG at lib/string_helpers.c:1048!
> Call Trace:
> [<00000000272502e2>] fortify_panic+0x2a/0x30
> ([<00000000272502de>] fortify_panic+0x26/0x30)
> [<001bffff817045c4>] kmalloc_oob_memset_2+0x22c/0x230 [kasan_test]
>
> Hide the `ptr` variable from the optimizer to fix the kernel panic.
> Also define a size2 variable and hide that as well. This cleans up
> the code and follows the same convention as other tests.
>
> Signed-off-by: Nico Pache <npache@xxxxxxxxxx>
> ---
>  mm/kasan/kasan_test.c | 20 ++++++++++++++++----
>  1 file changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/mm/kasan/kasan_test.c b/mm/kasan/kasan_test.c
> index 8281eb42464b..5aeba810ba70 100644
> --- a/mm/kasan/kasan_test.c
> +++ b/mm/kasan/kasan_test.c
> @@ -493,14 +493,17 @@ static void kmalloc_oob_memset_2(struct kunit *test)
>  {
>         char *ptr;
>         size_t size = 128 - KASAN_GRANULE_SIZE;
> +       size_t size2 = 2;

Let's name this variable access_size or memset_size. Here and in the
other changed tests.

>         KASAN_TEST_NEEDS_CHECKED_MEMINTRINSICS(test);
>
>         ptr = kmalloc(size, GFP_KERNEL);
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> +       OPTIMIZER_HIDE_VAR(ptr);
>         OPTIMIZER_HIDE_VAR(size);
> -       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 1, 0, 2));
> +       OPTIMIZER_HIDE_VAR(size2);
> +       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 1, 0, size2));
>         kfree(ptr);
>  }
>
> @@ -508,14 +511,17 @@ static void kmalloc_oob_memset_4(struct kunit *test)
>  {
>         char *ptr;
>         size_t size = 128 - KASAN_GRANULE_SIZE;
> +       size_t size2 = 4;
>
>         KASAN_TEST_NEEDS_CHECKED_MEMINTRINSICS(test);
>
>         ptr = kmalloc(size, GFP_KERNEL);
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> +       OPTIMIZER_HIDE_VAR(ptr);
>         OPTIMIZER_HIDE_VAR(size);
> -       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 3, 0, 4));
> +       OPTIMIZER_HIDE_VAR(size2);
> +       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 3, 0, size2));
>         kfree(ptr);
>  }
>
> @@ -523,14 +529,17 @@ static void kmalloc_oob_memset_8(struct kunit *test)
>  {
>         char *ptr;
>         size_t size = 128 - KASAN_GRANULE_SIZE;
> +       size_t size2 = 8;
>
>         KASAN_TEST_NEEDS_CHECKED_MEMINTRINSICS(test);
>
>         ptr = kmalloc(size, GFP_KERNEL);
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> +       OPTIMIZER_HIDE_VAR(ptr);
>         OPTIMIZER_HIDE_VAR(size);
> -       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 7, 0, 8));
> +       OPTIMIZER_HIDE_VAR(size2);
> +       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 7, 0, size2));
>         kfree(ptr);
>  }
>
> @@ -538,14 +547,17 @@ static void kmalloc_oob_memset_16(struct kunit *test)
>  {
>         char *ptr;
>         size_t size = 128 - KASAN_GRANULE_SIZE;
> +       size_t size2 = 16;
>
>         KASAN_TEST_NEEDS_CHECKED_MEMINTRINSICS(test);
>
>         ptr = kmalloc(size, GFP_KERNEL);
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> +       OPTIMIZER_HIDE_VAR(ptr);
>         OPTIMIZER_HIDE_VAR(size);
> -       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 15, 0, 16));
> +       OPTIMIZER_HIDE_VAR(size2);
> +       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 15, 0, size2));
>         kfree(ptr);
>  }
>
> --
> 2.43.0
>

With the fix mentioned above addressed:

Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>