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From:   Marco Elver <elver@google.com>
Date:   Thu, 12 Aug 2021 10:50:42 +0200
Message-ID: <CANpmjNMYJw9Qv48tsC-EVwKDeG9FWCwmf3SLZzATyfGoMDc2Qg@mail.gmail.com>
Subject: Re: [PATCH 7/8] kasan: test: avoid corrupting memory in copy_user_test
To:     andrey.konovalov@linux.dev
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Alexander Potapenko <glider@google.com>,
        kasan-dev@googlegroups.com, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
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On Wed, 11 Aug 2021 at 21:30, <andrey.konovalov@linux.dev> wrote:
> From: Andrey Konovalov <andreyknvl@gmail.com>
>
> copy_user_test() does writes past the allocated object. As the result,
> it corrupts kernel memory, which might lead to crashes with the HW_TAGS
> mode, as it neither uses quarantine nor redzones.
>
> (Technically, this test can't yet be enabled with the HW_TAGS mode, but
> this will be implemented in the future.)
>
> Adjust the test to only write memory within the aligned kmalloc object.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@gmail.com>

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


> ---
>  lib/test_kasan_module.c | 18 ++++++++----------
>  1 file changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/lib/test_kasan_module.c b/lib/test_kasan_module.c
> index f1017f345d6c..fa73b9df0be4 100644
> --- a/lib/test_kasan_module.c
> +++ b/lib/test_kasan_module.c
> @@ -15,13 +15,11 @@
>
>  #include "../mm/kasan/kasan.h"
>
> -#define OOB_TAG_OFF (IS_ENABLED(CONFIG_KASAN_GENERIC) ? 0 : KASAN_GRANULE_SIZE)
> -
>  static noinline void __init copy_user_test(void)
>  {
>         char *kmem;
>         char __user *usermem;
> -       size_t size = 10;
> +       size_t size = 128 - KASAN_GRANULE_SIZE;
>         int __maybe_unused unused;
>
>         kmem = kmalloc(size, GFP_KERNEL);
> @@ -38,25 +36,25 @@ static noinline void __init copy_user_test(void)
>         }
>
>         pr_info("out-of-bounds in copy_from_user()\n");
> -       unused = copy_from_user(kmem, usermem, size + 1 + OOB_TAG_OFF);
> +       unused = copy_from_user(kmem, usermem, size + 1);
>
>         pr_info("out-of-bounds in copy_to_user()\n");
> -       unused = copy_to_user(usermem, kmem, size + 1 + OOB_TAG_OFF);
> +       unused = copy_to_user(usermem, kmem, size + 1);
>
>         pr_info("out-of-bounds in __copy_from_user()\n");
> -       unused = __copy_from_user(kmem, usermem, size + 1 + OOB_TAG_OFF);
> +       unused = __copy_from_user(kmem, usermem, size + 1);
>
>         pr_info("out-of-bounds in __copy_to_user()\n");
> -       unused = __copy_to_user(usermem, kmem, size + 1 + OOB_TAG_OFF);
> +       unused = __copy_to_user(usermem, kmem, size + 1);
>
>         pr_info("out-of-bounds in __copy_from_user_inatomic()\n");
> -       unused = __copy_from_user_inatomic(kmem, usermem, size + 1 + OOB_TAG_OFF);
> +       unused = __copy_from_user_inatomic(kmem, usermem, size + 1);
>
>         pr_info("out-of-bounds in __copy_to_user_inatomic()\n");
> -       unused = __copy_to_user_inatomic(usermem, kmem, size + 1 + OOB_TAG_OFF);
> +       unused = __copy_to_user_inatomic(usermem, kmem, size + 1);
>
>         pr_info("out-of-bounds in strncpy_from_user()\n");
> -       unused = strncpy_from_user(kmem, usermem, size + 1 + OOB_TAG_OFF);
> +       unused = strncpy_from_user(kmem, usermem, size + 1);
>
>         vm_munmap((unsigned long)usermem, PAGE_SIZE);
>         kfree(kmem);
> --
> 2.25.1
>