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

From: Kees Cook <[email-masked]>
Date: Fri, 7 Jun 2019 21:03:43 -0700

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 <[email-masked]>

"userfaultfd: untag user pointers"

Reviewed-by: Kees Cook <[email-masked]>

-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

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