Re: [PATCH v16 09/16] fs, arm64: untag user pointers in fs/userfaultfd.c

Kees Cook
2019-06-08T04:03:51Z

On Mon, Jun 03, 2019 at 06:55:11PM +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.
>
> userfaultfd code use provided user pointers for vma lookups, which can
> only by done with untagged pointers.
>
> Untag user pointers in validate_range().
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

"userfaultfd: untag user pointers"

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

-Kees

> ---
> fs/userfaultfd.c | 22 ++++++++++++----------
> 1 file changed, 12 insertions(+), 10 deletions(-)
>
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index 3b30301c90ec..24d68c3b5ee2 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -1263,21 +1263,23 @@ static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
> }
>
> static __always_inline int validate_range(struct mm_struct *mm,
> - __u64 start, __u64 len)
> + __u64 *start, __u64 len)
> {
> __u64 task_size = mm->task_size;
>
> - if (start & ~PAGE_MASK)
> + *start = untagged_addr(*start);
> +
> + if (*start & ~PAGE_MASK)
> return -EINVAL;
> if (len & ~PAGE_MASK)
> return -EINVAL;
> if (!len)
> return -EINVAL;
> - if (start < mmap_min_addr)
> + if (*start < mmap_min_addr)
> return -EINVAL;
> - if (start >= task_size)
> + if (*start >= task_size)
> return -EINVAL;
> - if (len > task_size - start)
> + if (len > task_size - *start)
> return -EINVAL;
> return 0;
> }
> @@ -1327,7 +1329,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
> goto out;
> }
>
> - ret = validate_range(mm, uffdio_register.range.start,
> + ret = validate_range(mm, &uffdio_register.range.start,
> uffdio_register.range.len);
> if (ret)
> goto out;
> @@ -1516,7 +1518,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
> if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
> goto out;
>
> - ret = validate_range(mm, uffdio_unregister.start,
> + ret = validate_range(mm, &uffdio_unregister.start,
> uffdio_unregister.len);
> if (ret)
> goto out;
> @@ -1667,7 +1669,7 @@ static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
> if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
> goto out;
>
> - ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
> + ret = validate_range(ctx->mm, &uffdio_wake.start, uffdio_wake.len);
> if (ret)
> goto out;
>
> @@ -1707,7 +1709,7 @@ static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
> sizeof(uffdio_copy)-sizeof(__s64)))
> goto out;
>
> - ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
> + ret = validate_range(ctx->mm, &uffdio_copy.dst, uffdio_copy.len);
> if (ret)
> goto out;
> /*
> @@ -1763,7 +1765,7 @@ static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
> sizeof(uffdio_zeropage)-sizeof(__s64)))
> goto out;
>
> - ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
> + ret = validate_range(ctx->mm, &uffdio_zeropage.range.start,
> uffdio_zeropage.range.len);
> if (ret)
> goto out;
> --
> 2.22.0.rc1.311.g5d7573a151-goog
>

--
Kees Cook