Re: [PATCH v18 08/15] userfaultfd: untag user pointers

Catalin Marinas
2019-06-24T17:51:21Z

On Mon, Jun 24, 2019 at 04:32:53PM +0200, Andrey Konovalov wrote:
> This patch is a part of a series that extends 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().
>
> Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---
> fs/userfaultfd.c | 22 ++++++++++++----------
> 1 file changed, 12 insertions(+), 10 deletions(-)

Same here, it needs an ack from Al Viro.

> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index ae0b8b5f69e6..c2be36a168ca 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -1261,21 +1261,23 @@ 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;
> }
> @@ -1325,7 +1327,7 @@ 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;
> @@ -1514,7 +1516,7 @@ 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;
> @@ -1665,7 +1667,7 @@ 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;
>
> @@ -1705,7 +1707,7 @@ 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;
> /*
> @@ -1761,7 +1763,7 @@ 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;
> --
> 2.22.0.410.gd8fdbe21b5-goog