Re: [PATCH v18 11/15] IB/mlx4: untag user pointers in mlx4_get_umem_mr

[Kees Cook]

On Mon, Jun 24, 2019 at 04:32:56PM +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.
> 
> mlx4_get_umem_mr() uses provided user pointers for vma lookups, which can
> only by done with untagged pointers.
> 
> Untag user pointers in this function.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>

Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
>  drivers/infiniband/hw/mlx4/mr.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/infiniband/hw/mlx4/mr.c b/drivers/infiniband/hw/mlx4/mr.c
> index 355205a28544..13d9f917f249 100644
> --- a/drivers/infiniband/hw/mlx4/mr.c
> +++ b/drivers/infiniband/hw/mlx4/mr.c
> @@ -378,6 +378,7 @@ static struct ib_umem *mlx4_get_umem_mr(struct ib_udata *udata, u64 start,
>  	 * again
>  	 */
>  	if (!ib_access_writable(access_flags)) {
> +		unsigned long untagged_start = untagged_addr(start);
>  		struct vm_area_struct *vma;
>  
>  		down_read(&current->mm->mmap_sem);
> @@ -386,9 +387,9 @@ static struct ib_umem *mlx4_get_umem_mr(struct ib_udata *udata, u64 start,
>  		 * cover the memory, but for now it requires a single vma to
>  		 * entirely cover the MR to support RO mappings.
>  		 */
> -		vma = find_vma(current->mm, start);
> -		if (vma && vma->vm_end >= start + length &&
> -		    vma->vm_start <= start) {
> +		vma = find_vma(current->mm, untagged_start);
> +		if (vma && vma->vm_end >= untagged_start + length &&
> +		    vma->vm_start <= untagged_start) {
>  			if (vma->vm_flags & VM_WRITE)
>  				access_flags |= IB_ACCESS_LOCAL_WRITE;
>  		} else {
> -- 
> 2.22.0.410.gd8fdbe21b5-goog
> 

-- 
Kees Cook