From patchwork Thu Jan 28 13:04:41 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Paul Durrant X-Patchwork-Id: 12053647 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8802EC433E0 for ; Thu, 28 Jan 2021 13:05:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4195964DCE for ; Thu, 28 Jan 2021 13:05:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231687AbhA1NFh (ORCPT ); Thu, 28 Jan 2021 08:05:37 -0500 Received: from mail.xenproject.org ([104.130.215.37]:51948 "EHLO mail.xenproject.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231697AbhA1NFe (ORCPT ); Thu, 28 Jan 2021 08:05:34 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:Content-Type:MIME-Version: Message-Id:Date:Subject:Cc:To:From; bh=uSh/nbr5myWUoYd0uMZeNZLBjVL7y7b3A+YslUvvtUE=; b=di5UZsTvb+vMktgfuPpIFL3V6m kyJMyEUOv+AuBIACA13egD+cKHvoZtoTaVLq9n/vWH/H/PB6HACTzjgQc3vB0M7aV0QIGRWCBr3Ds bkyqs967pvFA729na7qb5vqnFSax+H5Roh7RWRct489JLpjBy3GYEj1akJtP5zEyPcgI=; Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1l56yb-0005yN-Fz; Thu, 28 Jan 2021 13:04:45 +0000 Received: from [54.239.6.186] (helo=localhost.localdomain) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1l56yb-0000K8-3m; Thu, 28 Jan 2021 13:04:45 +0000 From: Paul Durrant To: xen-devel@lists.xenproject.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Paul Durrant , Konrad Rzeszutek Wilk , =?utf-8?q?Roger_Pau_Monn?= =?utf-8?q?=C3=A9?= , Jens Axboe , Dongli Zhang Subject: [PATCH v2] xen-blkback: fix compatibility bug with single page rings Date: Thu, 28 Jan 2021 13:04:41 +0000 Message-Id: <20210128130441.11744-1-paul@xen.org> X-Mailer: git-send-email 2.17.1 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org From: Paul Durrant Prior to commit 4a8c31a1c6f5 ("xen/blkback: rework connect_ring() to avoid inconsistent xenstore 'ring-page-order' set by malicious blkfront"), the behaviour of xen-blkback when connecting to a frontend was: - read 'ring-page-order' - if not present then expect a single page ring specified by 'ring-ref' - else expect a ring specified by 'ring-refX' where X is between 0 and 1 << ring-page-order This was correct behaviour, but was broken by the afforementioned commit to become: - read 'ring-page-order' - if not present then expect a single page ring (i.e. ring-page-order = 0) - expect a ring specified by 'ring-refX' where X is between 0 and 1 << ring-page-order - if that didn't work then see if there's a single page ring specified by 'ring-ref' This incorrect behaviour works most of the time but fails when a frontend that sets 'ring-page-order' is unloaded and replaced by one that does not because, instead of reading 'ring-ref', xen-blkback will read the stale 'ring-ref0' left around by the previous frontend will try to map the wrong grant reference. This patch restores the original behaviour. Fixes: 4a8c31a1c6f5 ("xen/blkback: rework connect_ring() to avoid inconsistent xenstore 'ring-page-order' set by malicious blkfront") Signed-off-by: Paul Durrant Reviewed-by: Dongli Zhang Reviewed-by: Roger Pau Monné --- Cc: Konrad Rzeszutek Wilk Cc: "Roger Pau Monné" Cc: Jens Axboe Cc: Dongli Zhang v2: - Remove now-spurious error path special-case when nr_grefs == 1 --- drivers/block/xen-blkback/common.h | 1 + drivers/block/xen-blkback/xenbus.c | 38 +++++++++++++----------------- 2 files changed, 17 insertions(+), 22 deletions(-) diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h index b0c71d3a81a0..524a79f10de6 100644 --- a/drivers/block/xen-blkback/common.h +++ b/drivers/block/xen-blkback/common.h @@ -313,6 +313,7 @@ struct xen_blkif { struct work_struct free_work; unsigned int nr_ring_pages; + bool multi_ref; /* All rings for this device. */ struct xen_blkif_ring *rings; unsigned int nr_rings; diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index 9860d4842f36..6c5e9373e91c 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -998,14 +998,17 @@ static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir) for (i = 0; i < nr_grefs; i++) { char ring_ref_name[RINGREF_NAME_LEN]; - snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i); + if (blkif->multi_ref) + snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i); + else { + WARN_ON(i != 0); + snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref"); + } + err = xenbus_scanf(XBT_NIL, dir, ring_ref_name, "%u", &ring_ref[i]); if (err != 1) { - if (nr_grefs == 1) - break; - err = -EINVAL; xenbus_dev_fatal(dev, err, "reading %s/%s", dir, ring_ref_name); @@ -1013,18 +1016,6 @@ static int read_per_ring_refs(struct xen_blkif_ring *ring, const char *dir) } } - if (err != 1) { - WARN_ON(nr_grefs != 1); - - err = xenbus_scanf(XBT_NIL, dir, "ring-ref", "%u", - &ring_ref[0]); - if (err != 1) { - err = -EINVAL; - xenbus_dev_fatal(dev, err, "reading %s/ring-ref", dir); - return err; - } - } - err = -ENOMEM; for (i = 0; i < nr_grefs * XEN_BLKIF_REQS_PER_PAGE; i++) { req = kzalloc(sizeof(*req), GFP_KERNEL); @@ -1129,10 +1120,15 @@ static int connect_ring(struct backend_info *be) blkif->nr_rings, blkif->blk_protocol, protocol, blkif->vbd.feature_gnt_persistent ? "persistent grants" : ""); - ring_page_order = xenbus_read_unsigned(dev->otherend, - "ring-page-order", 0); - - if (ring_page_order > xen_blkif_max_ring_order) { + err = xenbus_scanf(XBT_NIL, dev->otherend, "ring-page-order", "%u", + &ring_page_order); + if (err != 1) { + blkif->nr_ring_pages = 1; + blkif->multi_ref = false; + } else if (ring_page_order <= xen_blkif_max_ring_order) { + blkif->nr_ring_pages = 1 << ring_page_order; + blkif->multi_ref = true; + } else { err = -EINVAL; xenbus_dev_fatal(dev, err, "requested ring page order %d exceed max:%d", @@ -1141,8 +1137,6 @@ static int connect_ring(struct backend_info *be) return err; } - blkif->nr_ring_pages = 1 << ring_page_order; - if (blkif->nr_rings == 1) return read_per_ring_refs(&blkif->rings[0], dev->otherend); else {