[PATCH v16 13/16] media/v4l2-core, arm64: untag user pointers in videobuf_dma_contig_user_get

[Kees Cook]

On Mon, Jun 03, 2019 at 06:55:15PM +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.
> 
> videobuf_dma_contig_user_get() uses provided user pointers for vma
> lookups, which can only by done with untagged pointers.
> 
> Untag the pointers in this function.
> 
> Acked-by: Mauro Carvalho Chehab <mchehab+samsung at kernel.org>
> Signed-off-by: Andrey Konovalov <andreyknvl at google.com>

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

-Kees

> ---
>  drivers/media/v4l2-core/videobuf-dma-contig.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/videobuf-dma-contig.c b/drivers/media/v4l2-core/videobuf-dma-contig.c
> index e1bf50df4c70..8a1ddd146b17 100644
> --- a/drivers/media/v4l2-core/videobuf-dma-contig.c
> +++ b/drivers/media/v4l2-core/videobuf-dma-contig.c
> @@ -160,6 +160,7 @@ static void videobuf_dma_contig_user_put(struct videobuf_dma_contig_memory *mem)
>  static int videobuf_dma_contig_user_get(struct videobuf_dma_contig_memory *mem,
>  					struct videobuf_buffer *vb)
>  {
> +	unsigned long untagged_baddr = untagged_addr(vb->baddr);
>  	struct mm_struct *mm = current->mm;
>  	struct vm_area_struct *vma;
>  	unsigned long prev_pfn, this_pfn;
> @@ -167,22 +168,22 @@ static int videobuf_dma_contig_user_get(struct videobuf_dma_contig_memory *mem,
>  	unsigned int offset;
>  	int ret;
>  
> -	offset = vb->baddr & ~PAGE_MASK;
> +	offset = untagged_baddr & ~PAGE_MASK;
>  	mem->size = PAGE_ALIGN(vb->size + offset);
>  	ret = -EINVAL;
>  
>  	down_read(&mm->mmap_sem);
>  
> -	vma = find_vma(mm, vb->baddr);
> +	vma = find_vma(mm, untagged_baddr);
>  	if (!vma)
>  		goto out_up;
>  
> -	if ((vb->baddr + mem->size) > vma->vm_end)
> +	if ((untagged_baddr + mem->size) > vma->vm_end)
>  		goto out_up;
>  
>  	pages_done = 0;
>  	prev_pfn = 0; /* kill warning */
> -	user_address = vb->baddr;
> +	user_address = untagged_baddr;
>  
>  	while (pages_done < (mem->size >> PAGE_SHIFT)) {
>  		ret = follow_pfn(vma, user_address, &this_pfn);
> -- 
> 2.22.0.rc1.311.g5d7573a151-goog
> 

-- 
Kees Cook