Re: [PATCH v14 10/17] fs, arm64: untag user pointers in fs/userfaultfd.c

[Catalin Marinas]

On Tue, Apr 30, 2019 at 03:25:06PM +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_register() and userfaultfd_unregister() use provided user
> pointers for vma lookups, which can only by done with untagged pointers.
> 
> Untag user pointers in these functions.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> ---
>  fs/userfaultfd.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
> index f5de1e726356..fdee0db0e847 100644
> --- a/fs/userfaultfd.c
> +++ b/fs/userfaultfd.c
> @@ -1325,6 +1325,9 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
>  		goto out;
>  	}
>  
> +	uffdio_register.range.start =
> +		untagged_addr(uffdio_register.range.start);
> +
>  	ret = validate_range(mm, uffdio_register.range.start,
>  			     uffdio_register.range.len);
>  	if (ret)
> @@ -1514,6 +1517,8 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
>  	if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
>  		goto out;
>  
> +	uffdio_unregister.start = untagged_addr(uffdio_unregister.start);
> +
>  	ret = validate_range(mm, uffdio_unregister.start,
>  			     uffdio_unregister.len);
>  	if (ret)

Wouldn't it be easier to do this in validate_range()? There are a few
more calls in this file, though I didn't check whether a tagged address
would cause issues.

-- 
Catalin