[PATCH v2] dmaengine: idxd: Do not enable user type Work Queue without Shared Virtual Addressing

[Fenghua Yu]

When the idxd_user_drv driver is bound to a Work Queue (WQ) device
without IOMMU or with IOMMU Passthrough without Shared Virtual
Addressing (SVA), the application gains direct access to physical
memory via the device by programming physical address to a submitted
descriptor. This allows direct userspace read and write access to
arbitrary physical memory. This is inconsistent with the security
goals of a good kernel API.

Unlike vfio_pci driver, the IDXD char device driver does not provide any
ways to pin user pages and translate the address from user VA to IOVA or
PA without IOMMU SVA. Therefore the application has no way to instruct the
device to perform DMA function. This makes the char device not usable for
normal application usage.

Since user type WQ without SVA cannot be used for normal application usage
and presents the security issue, bind idxd_user_drv driver and enable user
type WQ only when SVA is enabled (i.e. user PASID is enabled).

Fixes: 448c3de8ac83 ("dmaengine: idxd: create user driver for wq 'device'")
Cc: stable@xxxxxxxxxxxxxxx
Suggested-by: Arjan Van De Ven <arjan.van.de.ven@xxxxxxxxx>
Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>
---
v2:
- Update changlog per Dave Hansen's comments

 drivers/dma/idxd/cdev.c   | 18 ++++++++++++++++++
 include/uapi/linux/idxd.h |  1 +
 2 files changed, 19 insertions(+)

diff --git a/drivers/dma/idxd/cdev.c b/drivers/dma/idxd/cdev.c
index c2808fd081d6..a9b96b18772f 100644
--- a/drivers/dma/idxd/cdev.c
+++ b/drivers/dma/idxd/cdev.c
@@ -312,6 +312,24 @@ static int idxd_user_drv_probe(struct idxd_dev *idxd_dev)
 	if (idxd->state != IDXD_DEV_ENABLED)
 		return -ENXIO;
 
+	/*
+	 * User type WQ is enabled only when SVA is enabled for two reasons:
+	 *   - If no IOMMU or IOMMU Passthrough without SVA, userspace
+	 *     can directly access physical address through the WQ.
+	 *   - The IDXD cdev driver does not provide any ways to pin
+	 *     user pages and translate the address from user VA to IOVA or
+	 *     PA without IOMMU SVA. Therefore the application has no way
+	 *     to instruct the device to perform DMA function. This makes
+	 *     the cdev not usable for normal application usage.
+	 */
+	if (!device_user_pasid_enabled(idxd)) {
+		idxd->cmd_status = IDXD_SCMD_WQ_USER_NO_IOMMU;
+		dev_dbg(&idxd->pdev->dev,
+			"User type WQ cannot be enabled without SVA.\n");
+
+		return -EOPNOTSUPP;
+	}
+
 	mutex_lock(&wq->wq_lock);
 	wq->type = IDXD_WQT_USER;
 	rc = drv_enable_wq(wq);
diff --git a/include/uapi/linux/idxd.h b/include/uapi/linux/idxd.h
index 095299c75828..2b9e7feba3f3 100644
--- a/include/uapi/linux/idxd.h
+++ b/include/uapi/linux/idxd.h
@@ -29,6 +29,7 @@ enum idxd_scmd_stat {
 	IDXD_SCMD_WQ_NO_SIZE = 0x800e0000,
 	IDXD_SCMD_WQ_NO_PRIV = 0x800f0000,
 	IDXD_SCMD_WQ_IRQ_ERR = 0x80100000,
+	IDXD_SCMD_WQ_USER_NO_IOMMU = 0x80110000,
 };
 
 #define IDXD_SCMD_SOFTERR_MASK	0x80000000
-- 
2.32.0