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From:   Marco Elver <elver@google.com>
Date:   Thu, 12 Aug 2021 10:56:32 +0200
Message-ID: <CANpmjNMgkSG=QGKn-iOcUONTCxKtFHr2upbKcv46RsTYTcCx_Q@mail.gmail.com>
Subject: Re: [PATCH 6/8] kasan: test: clean up ksize_uaf
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 21:23, <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@gmail.com>
>
> Some KASAN tests use global variables to store function returns values
> so that the compiler doesn't optimize away these functions.
>
> ksize_uaf() doesn't call any functions, so it doesn't need to use
> kasan_int_result. Use volatile accesses instead, to be consistent with
> other similar tests.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@gmail.com>

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

Although I do wonder if the compiler might one day mess with the
volatile reads. At least this way we might also catch if the compiler
messes up volatile reads. ;-)

> ---
>  lib/test_kasan.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index efd0da5c750f..e159d24b3b49 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -731,8 +731,8 @@ static void ksize_uaf(struct kunit *test)
>         kfree(ptr);
>
>         KUNIT_EXPECT_KASAN_FAIL(test, ksize(ptr));
> -       KUNIT_EXPECT_KASAN_FAIL(test, kasan_int_result = *ptr);
> -       KUNIT_EXPECT_KASAN_FAIL(test, kasan_int_result = *(ptr + size));
> +       KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[0]);
> +       KUNIT_EXPECT_KASAN_FAIL(test, ((volatile char *)ptr)[size]);
>  }
>
>  static void kasan_stack_oob(struct kunit *test)
> --
> 2.25.1
>