Code:  static void make_response(struct xen_blkif_ring *ring, u64 id,
 			  unsigned short op, int st)
 {
	struct blkif_response  resp;
 	unsigned long     flags;
 	union blkif_back_rings *blk_rings;
 	int notify;
 
	resp.id        = id;
	resp.operation = op;
	resp.status    = st;
 	spin_lock_irqsave(&ring->blk_ring_lock, flags);
 	blk_rings = &ring->blk_rings;
 	/* Place on the response ring for the relevant domain. */
 	switch (ring->blkif->blk_protocol) {
 	case BLKIF_PROTOCOL_NATIVE:
		memcpy(RING_GET_RESPONSE(&blk_rings->native, blk_rings->native.rsp_prod_pvt),
		       &resp, sizeof(resp));
 		break;
 	case BLKIF_PROTOCOL_X86_32:
		memcpy(RING_GET_RESPONSE(&blk_rings->x86_32, blk_rings->x86_32.rsp_prod_pvt),
		       &resp, sizeof(resp));
 		break;
 	case BLKIF_PROTOCOL_X86_64:
		memcpy(RING_GET_RESPONSE(&blk_rings->x86_64, blk_rings->x86_64.rsp_prod_pvt),
		       &resp, sizeof(resp));
 		break;
 	default:
 		BUG();
 	}
 	blk_rings->common.rsp_prod_pvt++;
 	RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&blk_rings->common, notify);
 	spin_unlock_irqrestore(&ring->blk_ring_lock, flags);
	if (notify)
		notify_remote_via_irq(ring->irq);
}

Vulnerability Type: +Info 
CWE ID: CWE-200
Summary: The make_response function in drivers/block/xen-blkback/blkback.c in the Linux kernel before 4.11.8 allows guest OS users to obtain sensitive information from host OS (or other guest OS) kernel memory by leveraging the copying of uninitialized padding fields in Xen block-interface response structures, aka XSA-216.
Commit Message: xen-blkback: 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.

Cc: stable@vger.kernel.org

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>