Re: [RFC PATCH 1/1] device-dax: check for vma range while dax_mmap.

[Dave Jiang]

On 07/31/2018 04:46 AM, Zhang Yi wrote:
> It should be prevent user map an illegal vma range which larger than
> dax device phiscal resourse, as we don't have swap logic while page
> faulting in dax device.

This patch prevents a user mapping an illegal vma range that is larger
than a dax device physical resource.

> 
> Applications, especailly qemu, map the /dev/dax for virtual nvdimm's
> backend device, we defined the v-nvdimm label area at the end of mapped
> rang. By using an illegal size that exceeds the physical resource of
> /dev/dax, then it will triger qemu a signal fault while accessing these
> label area.

When qemu maps the dax device for virtual nvdimm's backend device, the
v-nvdimm label area is defined at the end of mapped range. By using an
illegal size that exceeds the range of the device dax, it will trigger a
fault with qemu.

> 
> Signed-off-by: Zhang Yi <yi.z.zhang@xxxxxxxxxxxxxxx>
> ---
>  drivers/dax/device.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/drivers/dax/device.c b/drivers/dax/device.c
> index aff2c15..c9a50cd 100644
> --- a/drivers/dax/device.c
> +++ b/drivers/dax/device.c
> @@ -177,6 +177,32 @@ static const struct attribute_group *dax_attribute_groups[] = {
>  	NULL,
>  };
>  
> +static int check_vma_range(struct dev_dax *dev_dax, struct vm_area_struct *vma,
> +		const char *func)
> +{
> +	struct device *dev = &dev_dax->dev;
> +	struct resource *res;
> +	unsigned long size;
> +	int ret, i;
> +
> +	if (!dax_alive(dev_dax->dax_dev))
> +		return -ENXIO;
> +
> +	size = vma->vm_end - vma->vm_start + (vma->vm_pgoff << PAGE_SHIFT);
> +	ret = -EINVAL;
> +	for (i = 0; i < dev_dax->num_resources; i++) {
> +		res = &dev_dax->res[i];
> +		if (size > resource_size(res)) {
> +			dev_info(dev, "%s: %s: fail, vma range is overflow\n",
> +				current->comm, func);
> +			ret = -EINVAL;
> +			continue;
> +		} else
> +			return 0;
> +	}
> +	return ret;
> +}
> +
>  static int check_vma(struct dev_dax *dev_dax, struct vm_area_struct *vma,
>  		const char *func)
>  {
> @@ -465,6 +491,8 @@ static int dax_mmap(struct file *filp, struct vm_area_struct *vma)
>  	 */
>  	id = dax_read_lock();
>  	rc = check_vma(dev_dax, vma, __func__);
> +	if (!rc)
> +		rc |= check_vma_range(dev_dax, vma, __func__);

I think you want to augment check_vma() rather than adding another
function? If this is added inside check_vma() then you can also skip the
!dax_alive() check. Do you expect this function to be called anywhere else?

>  	dax_read_unlock(id);
>  	if (rc)
>  		return rc;
>