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

[Zhang,Yi]

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