Re: [PATCH v16 15/16] vfio/type1, arm64: untag user pointers in vaddr_get_pfn

[Kees Cook]

On Mon, Jun 03, 2019 at 06:55:17PM +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.
> 
> vaddr_get_pfn() 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/vfio/vfio_iommu_type1.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 3ddc375e7063..528e39a1c2dd 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -384,6 +384,8 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
>  
>  	down_read(&mm->mmap_sem);
>  
> +	vaddr = untagged_addr(vaddr);
> +
>  	vma = find_vma_intersection(mm, vaddr, vaddr + 1);
>  
>  	if (vma && vma->vm_flags & VM_PFNMAP) {
> -- 
> 2.22.0.rc1.311.g5d7573a151-goog
> 

-- 
Kees Cook