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

[Zhang Yi]

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.

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.

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__);
 	dax_read_unlock(id);
 	if (rc)
 		return rc;
-- 
2.7.4