linux-kernel - Re: [PATCH v2] kunit: kasan_test: disable fortify string checker on kmalloc_oob

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Date: Thu, 14 Dec 2023 22:25:34 +0100
From: Andrey Konovalov <andreyknvl@...il.com>
To: Nico Pache <npache@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	kasan-dev@...glegroups.com, akpm@...ux-foundation.org, 
	vincenzo.frascino@....com, dvyukov@...gle.com, glider@...gle.com, 
	ryabinin.a.a@...il.com
Subject: Re: [PATCH v2] kunit: kasan_test: disable fortify string checker on kmalloc_oob_memset

On Thu, Dec 14, 2023 at 5:44 PM Nico Pache <npache@...hat.com> 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 memset_size 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@...hat.com>
> ---
>  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..34515a106ca5 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 memset_size = 2;
>
>         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(memset_size);
> +       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 1, 0, memset_size));
>         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 memset_size = 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(memset_size);
> +       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 3, 0, memset_size));
>         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 memset_size = 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(memset_size);
> +       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 7, 0, memset_size));
>         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 memset_size = 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(memset_size);
> +       KUNIT_EXPECT_KASAN_FAIL(test, memset(ptr + size - 15, 0, memset_size));
>         kfree(ptr);
>  }
>
> --
> 2.43.0
>

Reviewed-by: Andrey Konovalov <andreyknvl@...il.com>

Thanks!