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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Mon, 6 Jul 2020 08:19:33 +0200
Message-ID: <CACT4Y+akZ5iu2ohQhRqiUd8zkew-NmrUPrA=xYtS1xxHWZ60Og@mail.gmail.com>
Subject: Re: [PATCH v2] kasan: fix KASAN unit tests for tag-based KASAN
To:     Walter Wu <walter-zh.wu@mediatek.com>
Cc:     Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        wsd_upstream <wsd_upstream@mediatek.com>,
        linux-mediatek@lists.infradead.org,
        Andrey Konovalov <andreyknvl@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
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Sender: linux-kernel-owner@vger.kernel.org
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On Mon, Jul 6, 2020 at 4:21 AM Walter Wu <walter-zh.wu@mediatek.com> wrote:
>
> We use tag-based KASAN, then KASAN unit tests don't detect out-of-bounds
> memory access. They need to be fixed.
>
> With tag-based KASAN, the state of each 16 aligned bytes of memory is
> encoded in one shadow byte and the shadow value is tag of pointer, so
> we need to read next shadow byte, the shadow value is not equal to tag
> value of pointer, so that tag-based KASAN will detect out-of-bounds
> memory access.
>
> Signed-off-by: Walter Wu <walter-zh.wu@mediatek.com>
> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
> Cc: Dmitry Vyukov <dvyukov@google.com>
> Cc: Alexander Potapenko <glider@google.com>
> Cc: Matthias Brugger <matthias.bgg@gmail.com>
> Cc: Andrey Konovalov <andreyknvl@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> ---
>
> changes since v1:
> - Reduce amount of non-compiled code.
> - KUnit-KASAN Integration patchset are not merged yet. My patch should
>   have conflict with it, if needed, we can continue to wait it.
>
> ---
>
>  lib/test_kasan.c | 81 ++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 64 insertions(+), 17 deletions(-)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index e3087d90e00d..660664439d52 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -40,7 +40,11 @@ static noinline void __init kmalloc_oob_right(void)
>                 return;
>         }
>
> -       ptr[size] = 'x';
> +       if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> +               ptr[size] = 'x';
> +       else
> +               ptr[size + 5] = 'x';
> +

Hi Walter,

Would if be possible to introduce something like:

#define OOB_TAG_OFF (IS_ENABLED(CONFIG_KASAN_GENERIC) ? 0 : 8)

and then add it throughout as

        ptr[size + OOB_TAG_OFF] = 'x';

?
The current version results in quite some amount of additional code
that needs to be read, extended  and maintained in the future. So I am
thinking if it's possible to minimize it somehow...

>         kfree(ptr);
>  }
>
> @@ -92,7 +96,11 @@ static noinline void __init kmalloc_pagealloc_oob_right(void)
>                 return;
>         }
>
> -       ptr[size] = 0;
> +       if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> +               ptr[size] = 0;
> +       else
> +               ptr[size + 6] = 0;
> +
>         kfree(ptr);
>  }
>
> @@ -162,7 +170,11 @@ static noinline void __init kmalloc_oob_krealloc_more(void)
>                 return;
>         }
>
> -       ptr2[size2] = 'x';
> +       if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> +               ptr2[size2] = 'x';
> +       else
> +               ptr2[size2 + 13] = 'x';
> +
>         kfree(ptr2);
>  }
>
> @@ -180,7 +192,12 @@ static noinline void __init kmalloc_oob_krealloc_less(void)
>                 kfree(ptr1);
>                 return;
>         }
> -       ptr2[size2] = 'x';
> +
> +       if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> +               ptr2[size2] = 'x';
> +       else
> +               ptr2[size2 + 2] = 'x';
> +
>         kfree(ptr2);
>  }
>
> @@ -216,7 +233,11 @@ static noinline void __init kmalloc_oob_memset_2(void)
>                 return;
>         }
>
> -       memset(ptr+7, 0, 2);
> +       if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> +               memset(ptr+7, 0, 2);
> +       else
> +               memset(ptr+15, 0, 2);
> +
>         kfree(ptr);
>  }
>
> @@ -232,7 +253,11 @@ static noinline void __init kmalloc_oob_memset_4(void)
>                 return;
>         }
>
> -       memset(ptr+5, 0, 4);
> +       if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> +               memset(ptr+5, 0, 4);
> +       else
> +               memset(ptr+15, 0, 4);
> +
>         kfree(ptr);
>  }
>
> @@ -249,7 +274,11 @@ static noinline void __init kmalloc_oob_memset_8(void)
>                 return;
>         }
>
> -       memset(ptr+1, 0, 8);
> +       if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> +               memset(ptr+1, 0, 8);
> +       else
> +               memset(ptr+15, 0, 8);
> +
>         kfree(ptr);
>  }
>
> @@ -265,7 +294,11 @@ static noinline void __init kmalloc_oob_memset_16(void)
>                 return;
>         }
>
> -       memset(ptr+1, 0, 16);
> +       if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> +               memset(ptr+1, 0, 16);
> +       else
> +               memset(ptr+15, 0, 16);
> +
>         kfree(ptr);
>  }
>
> @@ -281,7 +314,11 @@ static noinline void __init kmalloc_oob_in_memset(void)
>                 return;
>         }
>
> -       memset(ptr, 0, size+5);
> +       if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> +               memset(ptr, 0, size+5);
> +       else
> +               memset(ptr, 0, size+7);
> +
>         kfree(ptr);
>  }
>
> @@ -415,7 +452,11 @@ static noinline void __init kmem_cache_oob(void)
>                 return;
>         }
>
> -       *p = p[size];
> +       if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> +               *p = p[size];
> +       else
> +               *p = p[size + 8];
> +
>         kmem_cache_free(cache, p);
>         kmem_cache_destroy(cache);
>  }
> @@ -497,6 +538,7 @@ static noinline void __init copy_user_test(void)
>         char __user *usermem;
>         size_t size = 10;
>         int unused;
> +       size_t oob_size;
>
>         kmem = kmalloc(size, GFP_KERNEL);
>         if (!kmem)
> @@ -511,26 +553,31 @@ static noinline void __init copy_user_test(void)
>                 return;
>         }
>
> +       if (IS_ENABLED(CONFIG_KASAN_GENERIC))
> +               oob_size = 1;
> +       else
> +               oob_size = 7;
> +
>         pr_info("out-of-bounds in copy_from_user()\n");
> -       unused = copy_from_user(kmem, usermem, size + 1);
> +       unused = copy_from_user(kmem, usermem, size + oob_size);
>
>         pr_info("out-of-bounds in copy_to_user()\n");
> -       unused = copy_to_user(usermem, kmem, size + 1);
> +       unused = copy_to_user(usermem, kmem, size + oob_size);
>
>         pr_info("out-of-bounds in __copy_from_user()\n");
> -       unused = __copy_from_user(kmem, usermem, size + 1);
> +       unused = __copy_from_user(kmem, usermem, size + oob_size);
>
>         pr_info("out-of-bounds in __copy_to_user()\n");
> -       unused = __copy_to_user(usermem, kmem, size + 1);
> +       unused = __copy_to_user(usermem, kmem, size + oob_size);
>
>         pr_info("out-of-bounds in __copy_from_user_inatomic()\n");
> -       unused = __copy_from_user_inatomic(kmem, usermem, size + 1);
> +       unused = __copy_from_user_inatomic(kmem, usermem, size + oob_size);
>
>         pr_info("out-of-bounds in __copy_to_user_inatomic()\n");
> -       unused = __copy_to_user_inatomic(usermem, kmem, size + 1);
> +       unused = __copy_to_user_inatomic(usermem, kmem, size + oob_size);
>
>         pr_info("out-of-bounds in strncpy_from_user()\n");
> -       unused = strncpy_from_user(kmem, usermem, size + 1);
> +       unused = strncpy_from_user(kmem, usermem, size + oob_size);
>
>         vm_munmap((unsigned long)usermem, PAGE_SIZE);
>         kfree(kmem);
> --
> 2.18.0
>
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