[PATCH 5.0 91/95] UAS: fix alignment of scatter/gather segments

Greg Kroah-Hartman
2019-05-09T18:53:44Z

From: Oliver Neukum <oneukum@suse.com>

commit 3ae62a42090f1ed48e2313ed256a1182a85fb575 upstream.

This is the UAS version of

747668dbc061b3e62bc1982767a3a1f9815fcf0e
usb-storage: Set virt_boundary_mask to avoid SG overflows

We are not as likely to be vulnerable as storage, as it is unlikelier
that UAS is run over a controller without native support for SG,
but the issue exists.
The issue has been existing since the inception of the driver.

Fixes: 115bb1ffa54c ("USB: Add UAS driver")
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/usb/storage/uas.c | 35 ++++++++++++++++++++++-------------
1 file changed, 22 insertions(+), 13 deletions(-)

--- a/drivers/usb/storage/uas.c
+++ b/drivers/usb/storage/uas.c
@@ -796,24 +796,33 @@ static int uas_slave_alloc(struct scsi_d
{
struct uas_dev_info *devinfo =
(struct uas_dev_info *)sdev->host->hostdata;
+ int maxp;

sdev->hostdata = devinfo;

/*
- * USB has unusual DMA-alignment requirements: Although the
- * starting address of each scatter-gather element doesn't matter,
- * the length of each element except the last must be divisible
- * by the Bulk maxpacket value. There's currently no way to
- * express this by block-layer constraints, so we'll cop out
- * and simply require addresses to be aligned at 512-byte
- * boundaries. This is okay since most block I/O involves
- * hardware sectors that are multiples of 512 bytes in length,
- * and since host controllers up through USB 2.0 have maxpacket
- * values no larger than 512.
+ * We have two requirements here. We must satisfy the requirements
+ * of the physical HC and the demands of the protocol, as we
+ * definitely want no additional memory allocation in this path
+ * ruling out using bounce buffers.
*
- * But it doesn't suffice for Wireless USB, where Bulk maxpacket
- * values can be as large as 2048. To make that work properly
- * will require changes to the block layer.
+ * For a transmission on USB to continue we must never send
+ * a package that is smaller than maxpacket. Hence the length of each
+ * scatterlist element except the last must be divisible by the
+ * Bulk maxpacket value.
+ * If the HC does not ensure that through SG,
+ * the upper layer must do that. We must assume nothing
+ * about the capabilities off the HC, so we use the most
+ * pessimistic requirement.
+ */
+
+ maxp = usb_maxpacket(devinfo->udev, devinfo->data_in_pipe, 0);
+ blk_queue_virt_boundary(sdev->request_queue, maxp - 1);
+
+ /*
+ * The protocol has no requirements on alignment in the strict sense.
+ * Controllers may or may not have alignment restrictions.
+ * As this is not exported, we use an extremely conservative guess.
*/
blk_queue_update_dma_alignment(sdev->request_queue, (512 - 1));