Re: [PATCH] kasan: fix KASAN unit tests for tag-based KASAN

[Dmitry Vyukov <dvyukov@google.com>]

On Tue, Apr 21, 2020 at 3:40 AM Walter Wu <walter-zh.wu@mediatek.com> wrote:
>
> When we use tag-based KASAN, then KASAN unit tests don't detect
> out-of-bounds memory access. Because 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 of pointer,
> then 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>
> ---
>  lib/test_kasan.c | 62 ++++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 55 insertions(+), 7 deletions(-)
>
> diff --git a/lib/test_kasan.c b/lib/test_kasan.c
> index e3087d90e00d..a164f6b47fe5 100644
> --- a/lib/test_kasan.c
> +++ b/lib/test_kasan.c
> @@ -40,7 +40,12 @@ static noinline void __init kmalloc_oob_right(void)
>                 return;
>         }

Hi Walter,

This would be great to have!
But I am concerned about these series that port KASAN tests to KUNIT:
https://lkml.org/lkml/2020/4/17/1144
I suspect it will be one large merge conflict. Not sure what is the
proper way to resovle this. I've added authors to CC.


> +#ifdef CONFIG_KASAN_GENERIC
>         ptr[size] = 'x';
> +#else
> +       ptr[size + 5] = 'x';
> +#endif
> +

For this particular snippet I think we can reduce amount of idef'ery
and amount of non-compiled code in each configuration with something
like:

  ptr[size + 5] = 'x';
  if (ENABLED(CONFIG_KASAN_GENERIC))
      ptr[size] = 'x';

One check runs always (it should pass in both configs, right?). The
only only in GENERIC, but it's C-level if rather than preprocessor.
KUNIT should make 2 bugs per test easily expressable (and testable).




>         kfree(ptr);
>  }
>
> @@ -92,7 +97,12 @@ static noinline void __init kmalloc_pagealloc_oob_right(void)
>                 return;
>         }
>
> +#ifdef CONFIG_KASAN_GENERIC
>         ptr[size] = 0;
> +#else
> +       ptr[size + 6] = 0;
> +#endif
> +
>         kfree(ptr);
>  }
>
> @@ -162,7 +172,11 @@ static noinline void __init kmalloc_oob_krealloc_more(void)
>                 return;
>         }
>
> +#ifdef CONFIG_KASAN_GENERIC
>         ptr2[size2] = 'x';
> +#else
> +       ptr2[size2 + 13] = 'x';
> +#endif
>         kfree(ptr2);
>  }
>
> @@ -180,7 +194,12 @@ static noinline void __init kmalloc_oob_krealloc_less(void)
>                 kfree(ptr1);
>                 return;
>         }
> +
> +#ifdef CONFIG_KASAN_GENERIC
>         ptr2[size2] = 'x';
> +#else
> +       ptr2[size2 + 2] = 'x';
> +#endif
>         kfree(ptr2);
>  }
>
> @@ -216,7 +235,11 @@ static noinline void __init kmalloc_oob_memset_2(void)
>                 return;
>         }
>
> +#ifdef CONFIG_KASAN_GENERIC
>         memset(ptr+7, 0, 2);
> +#else
> +       memset(ptr+15, 0, 2);
> +#endif
>         kfree(ptr);
>  }
>
> @@ -232,7 +255,11 @@ static noinline void __init kmalloc_oob_memset_4(void)
>                 return;
>         }
>
> +#ifdef CONFIG_KASAN_GENERIC
>         memset(ptr+5, 0, 4);
> +#else
> +       memset(ptr+15, 0, 4);
> +#endif
>         kfree(ptr);
>  }
>
> @@ -249,7 +276,11 @@ static noinline void __init kmalloc_oob_memset_8(void)
>                 return;
>         }
>
> +#ifdef CONFIG_KASAN_GENERIC
>         memset(ptr+1, 0, 8);
> +#else
> +       memset(ptr+15, 0, 8);
> +#endif
>         kfree(ptr);
>  }
>
> @@ -265,7 +296,11 @@ static noinline void __init kmalloc_oob_memset_16(void)
>                 return;
>         }
>
> +#ifdef CONFIG_KASAN_GENERIC
>         memset(ptr+1, 0, 16);
> +#else
> +       memset(ptr+15, 0, 16);
> +#endif
>         kfree(ptr);
>  }
>
> @@ -281,7 +316,11 @@ static noinline void __init kmalloc_oob_in_memset(void)
>                 return;
>         }
>
> +#ifdef CONFIG_KASAN_GENERIC
>         memset(ptr, 0, size+5);
> +#else
> +       memset(ptr, 0, size+7);
> +#endif
>         kfree(ptr);
>  }
>
> @@ -415,7 +454,11 @@ static noinline void __init kmem_cache_oob(void)
>                 return;
>         }
>
> +#ifdef CONFIG_KASAN_GENERIC
>         *p = p[size];
> +#else
> +       *p = p[size + 8];
> +#endif
>         kmem_cache_free(cache, p);
>         kmem_cache_destroy(cache);
>  }
> @@ -497,6 +540,11 @@ static noinline void __init copy_user_test(void)
>         char __user *usermem;
>         size_t size = 10;
>         int unused;
> +#ifdef CONFIG_KASAN_GENERIC
> +       size_t oob_size = 1;
> +#else
> +       size_t oob_size = 7;
> +#endif
>
>         kmem = kmalloc(size, GFP_KERNEL);
>         if (!kmem)
> @@ -512,25 +560,25 @@ 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);
> +       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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