Re: [PATCH v3] mm: x86: instrument __get/__put_kernel_nofault

[Andrey Konovalov <andreyknvl@gmail.com>]

On Thu, Sep 19, 2024 at 12:57 PM Sabyrzhan Tasbolatov
<snovitoll@gmail.com> wrote:
>
> On Wed, Sep 18, 2024 at 8:15 PM Andrey Konovalov <andreyknvl@gmail.com> wrote:
> > You still have the same problem here.
> >
> > What I meant is:
> >
> > char *ptr;
> > char buf[128 - KASAN_GRANULE_SIZE];
> > size_t size = sizeof(buf);
> >
> > ptr = kmalloc(size, GFP_KERNEL);
> > KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> >
> > KUNIT_EXPECT_KASAN_FAIL(...);
> > ...
> >
> > kfree(ptr);
>
> Thanks for catching this! I've turned kunit test into OOB instead of UAF.
> ---
> v3: changed kunit test from UAF to OOB case and git commit message.
> ---
> Instrument copy_from_kernel_nofault(), copy_to_kernel_nofault(),
> strncpy_from_kernel_nofault() where __put_kernel_nofault, __get_kernel_nofault
> macros are used.
>
> __get_kernel_nofault needs instrument_memcpy_before() which handles
> KASAN, KCSAN checks for src, dst address, whereas for __put_kernel_nofault
> macro, instrument_write() check should be enough as it's validated via
> kmsan_copy_to_user() in instrument_put_user().
>
> __get_user_size was appended with instrument_get_user() for KMSAN check in
> commit 888f84a6da4d("x86: asm: instrument usercopy in get_user() and
> put_user()") but only for CONFIG_CC_HAS_ASM_GOTO_OUTPUT.
>
> copy_from_to_kernel_nofault_oob() kunit test triggers 4 KASAN OOB bug reports
> as expected for each copy_from/to_kernel_nofault call.

"as expected for each" => "as expected, one for each"

>
> Reported-by: Andrey Konovalov <andreyknvl@gmail.com>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=210505
> Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
> ---
>  arch/x86/include/asm/uaccess.h |  4 ++++
>  mm/kasan/kasan_test.c          | 21 +++++++++++++++++++++
>  2 files changed, 25 insertions(+)
>
> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
> index 3a7755c1a441..87fb59071e8c 100644
> --- a/arch/x86/include/asm/uaccess.h
> +++ b/arch/x86/include/asm/uaccess.h
> @@ -353,6 +353,7 @@ do {                                                                        \
>         default:                                                        \
>                 (x) = __get_user_bad();                                 \
>         }                                                               \
> +       instrument_get_user(x);                                         \
>  } while (0)
>
>  #define __get_user_asm(x, addr, err, itype)                            \
> @@ -620,6 +621,7 @@ do {                                                                        \
>
>  #ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT
>  #define __get_kernel_nofault(dst, src, type, err_label)                        \
> +       instrument_memcpy_before(dst, src, sizeof(type));               \
>         __get_user_size(*((type *)(dst)), (__force type __user *)(src), \
>                         sizeof(type), err_label)
>  #else // !CONFIG_CC_HAS_ASM_GOTO_OUTPUT
> @@ -627,6 +629,7 @@ do {                                                                        \
>  do {                                                                   \
>         int __kr_err;                                                   \
>                                                                         \
> +       instrument_memcpy_before(dst, src, sizeof(type));               \
>         __get_user_size(*((type *)(dst)), (__force type __user *)(src), \
>                         sizeof(type), __kr_err);                        \
>         if (unlikely(__kr_err))                                         \
> @@ -635,6 +638,7 @@ do {                                                                        \
>  #endif // CONFIG_CC_HAS_ASM_GOTO_OUTPUT
>
>  #define __put_kernel_nofault(dst, src, type, err_label)                        \
> +       instrument_write(dst, sizeof(type));                            \
>         __put_user_size(*((type *)(src)), (__force type __user *)(dst), \
>                         sizeof(type), err_label)
>
> diff --git a/mm/kasan/kasan_test.c b/mm/kasan/kasan_test.c
> index 7b32be2a3cf0..d13f1a514750 100644
> --- a/mm/kasan/kasan_test.c
> +++ b/mm/kasan/kasan_test.c
> @@ -1899,6 +1899,26 @@ static void match_all_mem_tag(struct kunit *test)
>         kfree(ptr);
>  }
>
> +static void copy_from_to_kernel_nofault_oob(struct kunit *test)
> +{
> +       char *ptr;
> +       char buf[128];
> +       size_t size = sizeof(buf);
> +
> +       ptr = kmalloc(size - KASAN_GRANULE_SIZE, GFP_KERNEL);
> +       KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ptr);
> +
> +       KUNIT_EXPECT_KASAN_FAIL(test,
> +               copy_from_kernel_nofault(&buf[0], ptr, size));
> +       KUNIT_EXPECT_KASAN_FAIL(test,
> +               copy_from_kernel_nofault(ptr, &buf[0], size));
> +       KUNIT_EXPECT_KASAN_FAIL(test,
> +               copy_to_kernel_nofault(&buf[0], ptr, size));
> +       KUNIT_EXPECT_KASAN_FAIL(test,
> +               copy_to_kernel_nofault(ptr, &buf[0], size));
> +       kfree(ptr);
> +}
> +
>  static struct kunit_case kasan_kunit_test_cases[] = {
>         KUNIT_CASE(kmalloc_oob_right),
>         KUNIT_CASE(kmalloc_oob_left),
> @@ -1971,6 +1991,7 @@ static struct kunit_case kasan_kunit_test_cases[] = {
>         KUNIT_CASE(match_all_not_assigned),
>         KUNIT_CASE(match_all_ptr_tag),
>         KUNIT_CASE(match_all_mem_tag),
> +       KUNIT_CASE(copy_from_to_kernel_nofault_oob),
>         {}
>  };

The test looks good to me now.

But you need to send the patch as a standalone email, without
combining it with the response to my comment.

Thanks!