From: Jan Beulich <jbeulich@suse.com>
Subject: blkback/blktap: don't leak stack data via response ring

Rather than constructing a local structure instance on the stack, fill
the fields directly on the shared ring, just like other backends do.
Build on the fact that all response structure flavors are actually
identical (the old code did make this assumption too).

This is XSA-216.

Reported-by: Anthony Perard <anthony.perard@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

--- a/drivers/xen/blkback/blkback.c
+++ b/drivers/xen/blkback/blkback.c
@@ -606,33 +606,34 @@ static void _dispatch_rw_block_io(blkif_
 static void make_response(blkif_t *blkif, u64 id,
 			  unsigned short op, int st)
 {
-	blkif_response_t  resp;
+	blkif_response_t  *resp;
 	unsigned long     flags;
 	blkif_back_rings_t *blk_rings = &blkif->blk_rings;
 	int notify;
 
-	resp.id        = id;
-	resp.operation = op;
-	resp.status    = st;
-
 	spin_lock_irqsave(&blkif->blk_ring_lock, flags);
 	/* Place on the response ring for the relevant domain. */
 	switch (blkif->blk_protocol) {
 	case BLKIF_PROTOCOL_NATIVE:
-		memcpy(RING_GET_RESPONSE(&blk_rings->native, blk_rings->native.rsp_prod_pvt),
-		       &resp, sizeof(resp));
+		resp = RING_GET_RESPONSE(&blk_rings->native,
+					 blk_rings->native.rsp_prod_pvt);
 		break;
 	case BLKIF_PROTOCOL_X86_32:
-		memcpy(RING_GET_RESPONSE(&blk_rings->x86_32, blk_rings->x86_32.rsp_prod_pvt),
-		       &resp, sizeof(resp));
+		resp = RING_GET_RESPONSE(&blk_rings->x86_32,
+					 blk_rings->x86_32.rsp_prod_pvt);
 		break;
 	case BLKIF_PROTOCOL_X86_64:
-		memcpy(RING_GET_RESPONSE(&blk_rings->x86_64, blk_rings->x86_64.rsp_prod_pvt),
-		       &resp, sizeof(resp));
+		resp = RING_GET_RESPONSE(&blk_rings->x86_64,
+					 blk_rings->x86_64.rsp_prod_pvt);
 		break;
 	default:
 		BUG();
 	}
+
+	resp->id        = id;
+	resp->operation = op;
+	resp->status    = st;
+
 	blk_rings->common.rsp_prod_pvt++;
 	RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&blk_rings->common, notify);
 	spin_unlock_irqrestore(&blkif->blk_ring_lock, flags);
--- a/drivers/xen/blktap/blktap.c
+++ b/drivers/xen/blktap/blktap.c
@@ -1678,36 +1678,34 @@ static void dispatch_rw_block_io(blkif_t
 static void make_response(blkif_t *blkif, u64 id,
                           unsigned short op, int st)
 {
-	blkif_response_t  resp;
+	blkif_response_t  *resp;
 	unsigned long     flags;
 	blkif_back_rings_t *blk_rings = &blkif->blk_rings;
 	int notify;
 
-	resp.id        = id;
-	resp.operation = op;
-	resp.status    = st;
-
 	spin_lock_irqsave(&blkif->blk_ring_lock, flags);
 	/* Place on the response ring for the relevant domain. */
 	switch (blkif->blk_protocol) {
 	case BLKIF_PROTOCOL_NATIVE:
-		memcpy(RING_GET_RESPONSE(&blk_rings->native,
-					 blk_rings->native.rsp_prod_pvt),
-		       &resp, sizeof(resp));
+		resp = RING_GET_RESPONSE(&blk_rings->native,
+					 blk_rings->native.rsp_prod_pvt);
 		break;
 	case BLKIF_PROTOCOL_X86_32:
-		memcpy(RING_GET_RESPONSE(&blk_rings->x86_32,
-					 blk_rings->x86_32.rsp_prod_pvt),
-		       &resp, sizeof(resp));
+		resp = RING_GET_RESPONSE(&blk_rings->x86_32,
+					 blk_rings->x86_32.rsp_prod_pvt);
 		break;
 	case BLKIF_PROTOCOL_X86_64:
-		memcpy(RING_GET_RESPONSE(&blk_rings->x86_64,
-					 blk_rings->x86_64.rsp_prod_pvt),
-		       &resp, sizeof(resp));
+		resp = RING_GET_RESPONSE(&blk_rings->x86_64,
+					 blk_rings->x86_64.rsp_prod_pvt);
 		break;
 	default:
 		BUG();
 	}
+
+	resp->id        = id;
+	resp->operation = op;
+	resp->status    = st;
+
 	blk_rings->common.rsp_prod_pvt++;
 	RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&blk_rings->common, notify);
 
--- a/include/xen/blkif.h
+++ b/include/xen/blkif.h
@@ -32,9 +32,6 @@
 struct blkif_common_request {
 	char dummy;
 };
-struct blkif_common_response {
-	char dummy;
-};
 
 /* i386 protocol version */
 #pragma pack(push, 4)
@@ -46,13 +43,7 @@ union blkif_x86_32_union {
 	blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
 	struct blkif_request_segment seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
 };
-struct blkif_x86_32_response {
-	uint64_t        id;              /* copied from request */
-	uint8_t         operation;       /* copied from request */
-	int16_t         status;          /* BLKIF_RSP_???       */
-};
 typedef struct blkif_x86_32_request blkif_x86_32_request_t;
-typedef struct blkif_x86_32_response blkif_x86_32_response_t;
 #pragma pack(pop)
 
 /* x86_64 protocol version */
@@ -64,18 +55,15 @@ union blkif_x86_64_union {
 	blkif_sector_t sector_number;/* start sector idx on disk (r/w only)  */
 	struct blkif_request_segment seg[BLKIF_MAX_SEGMENTS_PER_REQUEST];
 };
-struct blkif_x86_64_response {
-	uint64_t       __attribute__((__aligned__(8))) id;
-	uint8_t         operation;       /* copied from request */
-	int16_t         status;          /* BLKIF_RSP_???       */
-};
 typedef struct blkif_x86_64_request blkif_x86_64_request_t;
-typedef struct blkif_x86_64_response blkif_x86_64_response_t;
 
 #define blkif_native_sring blkif_sring
-DEFINE_RING_TYPES(blkif_common, struct blkif_common_request, struct blkif_common_response);
-DEFINE_RING_TYPES(blkif_x86_32, struct blkif_x86_32_request, struct blkif_x86_32_response);
-DEFINE_RING_TYPES(blkif_x86_64, struct blkif_x86_64_request, struct blkif_x86_64_response);
+DEFINE_RING_TYPES(blkif_common, struct blkif_common_request,
+		  struct blkif_response);
+DEFINE_RING_TYPES(blkif_x86_32, struct blkif_x86_32_request,
+		  struct blkif_response __attribute__((__packed__)));
+DEFINE_RING_TYPES(blkif_x86_64, struct blkif_x86_64_request,
+		  struct blkif_response);
 
 union blkif_back_rings {
 	blkif_back_ring_t        native;