Re: [PATCH v16 07/16] mm, arm64: untag user pointers in get_vaddr_frames

Kees Cook
2019-06-08T04:00:29Z

On Mon, Jun 03, 2019 at 06:55:09PM +0200, Andrey Konovalov wrote:
> This patch is a part of a series that extends arm64 kernel ABI to allow to
> pass tagged user pointers (with the top byte set to something else other
> than 0x00) as syscall arguments.
>
> get_vaddr_frames uses provided user pointers for vma lookups, which can
> only by done with untagged pointers. Instead of locating and changing
> all callers of this function, perform untagging in it.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
> mm/frame_vector.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/mm/frame_vector.c b/mm/frame_vector.c
> index c64dca6e27c2..c431ca81dad5 100644
> --- a/mm/frame_vector.c
> +++ b/mm/frame_vector.c
> @@ -46,6 +46,8 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
> if (WARN_ON_ONCE(nr_frames > vec->nr_allocated))
> nr_frames = vec->nr_allocated;
>
> + start = untagged_addr(start);
> +
> down_read(&mm->mmap_sem);
> locked = 1;
> vma = find_vma_intersection(mm, start, start + 1);
> --
> 2.22.0.rc1.311.g5d7573a151-goog
>

--
Kees Cook