Re: [RFC PATCH v5 08/11] VFIO_PLATFORM: Support MMAP of MMIO regions

[Alex Williamson <alex.williamson-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Mon, 2014-04-28 at 17:52 +0200, Antonios Motakis wrote:
> Allow to memory map the MMIO regions of the device so userspace can
> directly access them.
> 
> Signed-off-by: Antonios Motakis <a.motakis-lrHrjnjw1UfHK3s98zE1ajGjJy/sRE9J@public.gmane.org>
> ---
>  drivers/vfio/platform/vfio_platform.c | 40 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 39 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vfio/platform/vfio_platform.c b/drivers/vfio/platform/vfio_platform.c
> index 7c01ced..37beff3 100644
> --- a/drivers/vfio/platform/vfio_platform.c
> +++ b/drivers/vfio/platform/vfio_platform.c
> @@ -58,6 +58,11 @@ static int vfio_platform_regions_init(struct vfio_platform_device *vdev)
>  		region.flags = VFIO_REGION_INFO_FLAG_READ
>  				| VFIO_REGION_INFO_FLAG_WRITE;
>  
> +		/* Only regions addressed with PAGE granularity can be MMAPed
> +		 * securely. */
> +		if (!(region.addr & ~PAGE_MASK) && !(region.size & ~PAGE_MASK))
> +			region.flags |= VFIO_REGION_INFO_FLAG_MMAP;
> +

Ok, so the security is only that we need page alignment.  Maybe that
could be made more clear in the previous patch.  PCI has regions like
the MSI-X table that we need to protect from userspace access beyond
page alignment requirements.  Thanks,

Alex

>  		vdev->region[i] = region;
>  	}
>  
> @@ -268,7 +273,40 @@ err:
>  
>  static int vfio_platform_mmap(void *device_data, struct vm_area_struct *vma)
>  {
> -	return -EINVAL;
> +	struct vfio_platform_device *vdev = device_data;
> +	unsigned int index;
> +	u64 req_len, pgoff, req_start;
> +	struct vfio_platform_region region;
> +
> +	index = vma->vm_pgoff >> (VFIO_PLATFORM_OFFSET_SHIFT - PAGE_SHIFT);
> +
> +	if (vma->vm_end < vma->vm_start)
> +		return -EINVAL;
> +	if ((vma->vm_flags & VM_SHARED) == 0)
> +		return -EINVAL;
> +	if (index >= vdev->num_regions)
> +		return -EINVAL;
> +	if (vma->vm_start & ~PAGE_MASK)
> +		return -EINVAL;
> +	if (vma->vm_end & ~PAGE_MASK)
> +		return -EINVAL;
> +
> +	region = vdev->region[index];
> +
> +	req_len = vma->vm_end - vma->vm_start;
> +	pgoff = vma->vm_pgoff &
> +		((1U << (VFIO_PLATFORM_OFFSET_SHIFT - PAGE_SHIFT)) - 1);
> +	req_start = pgoff << PAGE_SHIFT;
> +
> +	if (region.size < PAGE_SIZE || req_start + req_len > region.size)
> +		return -EINVAL;
> +
> +	vma->vm_private_data = vdev;
> +	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> +	vma->vm_pgoff = (region.addr >> PAGE_SHIFT) + pgoff;
> +
> +	return remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
> +			       req_len, vma->vm_page_prot);
>  }
>  
>  static const struct vfio_device_ops vfio_platform_ops = {