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

[Fenghua Yu]

Userspace can directly access physical address through user type
Work Queue (WQ) in two scenarios: no IOMMU or IOMMU Passthrough
without Shared Virtual Addressing (SVA). In these two cases, user type WQ
allows userspace to issue DMA physical address access without virtual
to physical translation.

This is inconsistent with the security goals of a good kernel API.

Plus there is no usage for user type WQ without SVA.

So enable user type WQ only when SVA is enabled (i.e. user PASID is
enabled).

Fixes: 42d279f9137a ("dmaengine: idxd: add char driver to expose submission portal to userland")

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>
---
 drivers/dma/idxd/cdev.c   | 14 ++++++++++++++
 include/uapi/linux/idxd.h |  1 +
 2 files changed, 15 insertions(+)

diff --git a/drivers/dma/idxd/cdev.c b/drivers/dma/idxd/cdev.c
index c2808fd081d6..4cd3400c5a48 100644
--- a/drivers/dma/idxd/cdev.c
+++ b/drivers/dma/idxd/cdev.c
@@ -312,6 +312,20 @@ 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.
+	 *   - There is no usage case for the WQ without SVA.
+	 */
+	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