linux-kernel - [PATCH 4.8 081/138] virtio_pci: Limit DMA mask to 44 bits for legacy virtio devices

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Message-Id: <20161109102848.582213068@linuxfoundation.org>
Date:   Wed,  9 Nov 2016 11:46:04 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Benjamin Serebrin <serebrin@...gle.com>,
        Will Deacon <will.deacon@....com>
Subject: [PATCH 4.8 081/138] virtio_pci: Limit DMA mask to 44 bits for legacy virtio devices

4.8-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Will Deacon <will.deacon@....com>

commit a0be1db4304f51c99af6b6e515549794182a94df upstream.

Legacy virtio defines the virtqueue base using a 32-bit PFN field, with
a read-only register indicating a fixed page size of 4k.

This can cause problems for DMA allocators that allocate top down from
the DMA mask, which is set to 64 bits. In this case, the addresses are
silently truncated to 44-bit, leading to IOMMU faults, failure to read
from the queue or data corruption.

This patch restricts the coherent DMA mask for legacy PCI virtio devices
to 44 bits, which matches the specification.

Cc: Andy Lutomirski <luto@...nel.org>
Cc: Michael S. Tsirkin <mst@...hat.com>
Cc: Benjamin Serebrin <serebrin@...gle.com>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/virtio/virtio_pci_legacy.c |   16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

--- a/drivers/virtio/virtio_pci_legacy.c
+++ b/drivers/virtio/virtio_pci_legacy.c
@@ -212,10 +212,18 @@ int virtio_pci_legacy_probe(struct virti
 		return -ENODEV;
 	}

-	rc = dma_set_mask_and_coherent(&pci_dev->dev, DMA_BIT_MASK(64));
-	if (rc)
-		rc = dma_set_mask_and_coherent(&pci_dev->dev,
-						DMA_BIT_MASK(32));
+	rc = dma_set_mask(&pci_dev->dev, DMA_BIT_MASK(64));
+	if (rc) {
+		rc = dma_set_mask_and_coherent(&pci_dev->dev, DMA_BIT_MASK(32));
+	} else {
+		/*
+		 * The virtio ring base address is expressed as a 32-bit PFN,
+		 * with a page size of 1 << VIRTIO_PCI_QUEUE_ADDR_SHIFT.
+		 */
+		dma_set_coherent_mask(&pci_dev->dev,
+				DMA_BIT_MASK(32 + VIRTIO_PCI_QUEUE_ADDR_SHIFT));
+	}
+
 	if (rc)
 		dev_warn(&pci_dev->dev, "Failed to enable 64-bit or 32-bit DMA.  Trying to continue, but this might not work.\n");