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

[Zhang,Yi]

On 2018å08æ08æ 08:05, Dave Jiang wrote:
>
> On 08/02/2018 02:32 AM, Zhang,Yi wrote:
>>
>> On 2018å08æ02æ 03:40, Dave Jiang wrote:
>>> 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.
>> Thanks Dava, that's could be much better.
>>>> 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 don't see any reason to logical or the return code. It should be 0, so
> you can just assign it to check_vma_range().
Ah.. Yes, Thanks for your kindly review, Dace, I will send the next version.
>
>>> 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?
>> since check_vma range also will be called while dax page faulting.  I
>> don't wanna this check_vma_range introduce some additional workload
>> while page fault. just let it checked in the mmap scenario
> Good point. Ok.
>
>>>>  	dax_read_unlock(id);
>>>>  	if (rc)
>>>>  		return rc;
>>>>