linux-kernel - Re: [PATCH 2/8] kasan: test: avoid writing invalid memory

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Message-ID: <CANpmjNM6hn8UrozaptUacuNJ7EtsprDJWDmOk-F6BaNZ6Hgchg@mail.gmail.com>
Date:   Thu, 12 Aug 2021 10:57:11 +0200
From:   Marco Elver <elver@...gle.com>
To:     andrey.konovalov@...ux.dev
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/8] kasan: test: avoid writing invalid memory

On Wed, 11 Aug 2021 at 21:21, <andrey.konovalov@...ux.dev> wrote:
> From: Andrey Konovalov <andreyknvl@...il.com>
>
> Multiple KASAN tests do writes past the allocated objects or writes to
> freed memory. Turn these writes into reads to avoid corrupting memory.
> Otherwise, these tests might lead to crashes with the HW_TAGS mode, as it
> neither uses quarantine nor redzones.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@...il.com>

Reviewed-by: Marco Elver <elver@...gle.com>

although if you need a write primitive somewhere that doesn't corrupt
memory, you could use atomic_add() or atomic_or() of 0. Although
technically that's a read-modify-write. For generic mode one issue is
that these are explicitly instrumented and not through the compiler,
which is only a problem if you're testing the compiler emits the right
instrumentation.


> ---
>  lib/test_kasan.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index 1bc3cdd2957f..c82a82eb5393 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -167,7 +167,7 @@ static void kmalloc_node_oob_right(struct kunit *test)
>         ptr = kmalloc_node(size, GFP_KERNEL, 0);
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> -       KUNIT_EXPECT_KASAN_FAIL(test, ptr[size] = 0);
> +       KUNIT_EXPECT_KASAN_FAIL(test, ptr[0] = ptr[size]);
>         kfree(ptr);
>  }
>
> @@ -203,7 +203,7 @@ static void kmalloc_pagealloc_uaf(struct kunit *test)
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>         kfree(ptr);
>
> -       KUNIT_EXPECT_KASAN_FAIL(test, ptr[0] = 0);
> +       KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[0]);
>  }
>
>  static void kmalloc_pagealloc_invalid_free(struct kunit *test)
> @@ -237,7 +237,7 @@ static void pagealloc_oob_right(struct kunit *test)
>         ptr = page_address(pages);
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
> -       KUNIT_EXPECT_KASAN_FAIL(test, ptr[size] = 0);
> +       KUNIT_EXPECT_KASAN_FAIL(test, ptr[0] = ptr[size]);
>         free_pages((unsigned long)ptr, order);
>  }
>
> @@ -252,7 +252,7 @@ static void pagealloc_uaf(struct kunit *test)
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>         free_pages((unsigned long)ptr, order);
>
> -       KUNIT_EXPECT_KASAN_FAIL(test, ptr[0] = 0);
> +       KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[0]);
>  }
>
>  static void kmalloc_large_oob_right(struct kunit *test)
> @@ -514,7 +514,7 @@ static void kmalloc_uaf(struct kunit *test)
>         KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
>
>         kfree(ptr);
> -       KUNIT_EXPECT_KASAN_FAIL(test, *(ptr + 8) = 'x');
> +       KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[8]);
>  }
>
>  static void kmalloc_uaf_memset(struct kunit *test)
> @@ -553,7 +553,7 @@ static void kmalloc_uaf2(struct kunit *test)
>                 goto again;
>         }
>
> -       KUNIT_EXPECT_KASAN_FAIL(test, ptr1[40] = 'x');
> +       KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr1)[40]);
>         KUNIT_EXPECT_PTR_NE(test, ptr1, ptr2);
>
>         kfree(ptr2);
> @@ -700,7 +700,7 @@ static void ksize_unpoisons_memory(struct kunit *test)
>         ptr[size] = 'x';
>
>         /* This one must. */
> -       KUNIT_EXPECT_KASAN_FAIL(test, ptr[real_size] = 'y');
> +       KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[real_size]);
>
>         kfree(ptr);
>  }
> --
> 2.25.1
>
> --
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