qubes-linux-kernel/patches.xen/xsa155-linux44-0013-xen-blkfront-prepare-request-locally-only-then-put-i.patch

From 74aaa42e1f25309a163acd00083ecbbc186fbb47 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marek=20Marczykowski-G=C3=B3recki?=
 <marmarek@invisiblethingslab.com>
Date: Wed, 16 Dec 2015 06:07:14 +0100
Subject: [PATCH 13/13] xen-blkfront: prepare request locally, only then put it
 on the shared ring
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Organization: Invisible Things Lab
Cc: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>

Do not reuse data which theoretically might be already modified by the
backend. This is mostly about private copy of the request
(info->shadow[id].req) - make sure the request saved there is really the
one just filled.

This is part of XSA155.

CC: stable@vger.kernel.org
Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
---
 drivers/block/xen-blkfront.c | 56 ++++++++++++++++++++++++--------------------
 1 file changed, 30 insertions(+), 26 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 5d7eb04..514cf18 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -463,27 +463,29 @@ static int blkif_ioctl(struct block_devi
 static int blkif_queue_discard_req(struct request *req)
 {
 	struct blkfront_info *info = req->rq_disk->private_data;
-	struct blkif_request *ring_req;
+	struct blkif_request ring_req = { };
 	unsigned long id;
 
 	/* Fill out a communications ring structure. */
-	ring_req = RING_GET_REQUEST(&info->ring, info->ring.req_prod_pvt);
 	id = get_id_from_freelist(info);
 	info->shadow[id].request = req;
 
-	ring_req->operation = BLKIF_OP_DISCARD;
-	ring_req->u.discard.nr_sectors = blk_rq_sectors(req);
-	ring_req->u.discard.id = id;
-	ring_req->u.discard.sector_number = (blkif_sector_t)blk_rq_pos(req);
+	ring_req.operation = BLKIF_OP_DISCARD;
+	ring_req.u.discard.nr_sectors = blk_rq_sectors(req);
+	ring_req.u.discard.id = id;
+	ring_req.u.discard.sector_number = (blkif_sector_t)blk_rq_pos(req);
 	if ((req->cmd_flags & REQ_SECURE) && info->feature_secdiscard)
-		ring_req->u.discard.flag = BLKIF_DISCARD_SECURE;
+		ring_req.u.discard.flag = BLKIF_DISCARD_SECURE;
 	else
-		ring_req->u.discard.flag = 0;
+		ring_req.u.discard.flag = 0;
 
+	/* make the request available to the backend */
+	*RING_GET_REQUEST(&info->ring, info->ring.req_prod_pvt) = ring_req;
+	wmb();
 	info->ring.req_prod_pvt++;
 
 	/* Keep a private copy so we can reissue requests when recovering. */
-	info->shadow[id].req = *ring_req;
+	info->shadow[id].req = ring_req;
 
 	return 0;
 }
@@ -573,7 +575,7 @@ static void blkif_setup_rw_req_grant(uns
 static int blkif_queue_rw_req(struct request *req)
 {
 	struct blkfront_info *info = req->rq_disk->private_data;
-	struct blkif_request *ring_req;
+	struct blkif_request ring_req = { };
 	unsigned long id;
 	int i;
 	struct setup_rw_req setup = {
@@ -435,7 +435,6 @@
 		new_persistent_gnts = 0;
 
 	/* Fill out a communications ring structure. */
-	ring_req = RING_GET_REQUEST(&info->ring, info->ring.req_prod_pvt);
 	id = get_id_from_freelist(info);
 	info->shadow[id].request = req;
 
@@ -632,7 +633,7 @@ static int blkif_queue_rw_req(struct req
 	for_each_sg(info->shadow[id].sg, sg, num_sg, i)
 	       num_grant += gnttab_count_grant(sg->offset, sg->length);
 
-	ring_req->u.rw.id = id;
+	ring_req.u.rw.id = id;
 	info->shadow[id].num_sg = num_sg;
 	if (num_grant > BLKIF_MAX_SEGMENTS_PER_REQUEST) {
 		/*
@@ -640,16 +641,16 @@ static int blkif_queue_rw_req(struct req
 		 * BLKIF_OP_WRITE
 		 */
 		BUG_ON(req->cmd_flags & (REQ_FLUSH | REQ_FUA));
-		ring_req->operation = BLKIF_OP_INDIRECT;
-		ring_req->u.indirect.indirect_op = rq_data_dir(req) ?
+		ring_req.operation = BLKIF_OP_INDIRECT;
+		ring_req.u.indirect.indirect_op = rq_data_dir(req) ?
 			BLKIF_OP_WRITE : BLKIF_OP_READ;
-		ring_req->u.indirect.sector_number = (blkif_sector_t)blk_rq_pos(req);
-		ring_req->u.indirect.handle = info->handle;
-		ring_req->u.indirect.nr_segments = num_grant;
+		ring_req.u.indirect.sector_number = (blkif_sector_t)blk_rq_pos(req);
+		ring_req.u.indirect.handle = info->handle;
+		ring_req.u.indirect.nr_segments = num_grant;
 	} else {
-		ring_req->u.rw.sector_number = (blkif_sector_t)blk_rq_pos(req);
-		ring_req->u.rw.handle = info->handle;
-		ring_req->operation = rq_data_dir(req) ?
+		ring_req.u.rw.sector_number = (blkif_sector_t)blk_rq_pos(req);
+		ring_req.u.rw.handle = info->handle;
+		ring_req.operation = rq_data_dir(req) ?
 			BLKIF_OP_WRITE : BLKIF_OP_READ;
 		if (req->cmd_flags & (REQ_FLUSH | REQ_FUA)) {
 			/*
@@ -662,21 +663,21 @@ static int blkif_queue_rw_req(struct req
 			switch (info->feature_flush &
 				((REQ_FLUSH|REQ_FUA))) {
 			case REQ_FLUSH|REQ_FUA:
-				ring_req->operation =
+				ring_req.operation =
 					BLKIF_OP_WRITE_BARRIER;
 				break;
 			case REQ_FLUSH:
-				ring_req->operation =
+				ring_req.operation =
 					BLKIF_OP_FLUSH_DISKCACHE;
 				break;
 			default:
-				ring_req->operation = 0;
+				ring_req.operation = 0;
 			}
 		}
-		ring_req->u.rw.nr_segments = num_grant;
+		ring_req.u.rw.nr_segments = num_grant;
 	}
 
-	setup.ring_req = ring_req;
+	setup.ring_req = &ring_req;
 	setup.id = id;
 	for_each_sg(info->shadow[id].sg, sg, num_sg, i) {
 		BUG_ON(sg->offset + sg->length > PAGE_SIZE);
@@ -698,10 +699,13 @@ static int blkif_queue_rw_req(struct req
 	if (setup.segments)
 		kunmap_atomic(setup.segments);
 
+	/* make the request available to the backend */
+	*RING_GET_REQUEST(&info->ring, info->ring.req_prod_pvt) = ring_req;
+	wmb();
 	info->ring.req_prod_pvt++;
 
 	/* Keep a private copy so we can reissue requests when recovering. */
-	info->shadow[id].req = *ring_req;
+	info->shadow[id].req = ring_req;
 
 	if (new_persistent_gnts)
 		gnttab_free_grant_references(setup.gref_head);