From nobody Sun Apr 28 15:06:38 2024 Delivered-To: importer@patchew.org Received-SPF: pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) client-ip=192.237.175.120; envelope-from=xen-devel-bounces@lists.xenproject.org; helo=lists.xenproject.org; Authentication-Results: mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) smtp.mailfrom=xen-devel-bounces@lists.xenproject.org ARC-Seal: i=1; a=rsa-sha256; t=1611838558; cv=none; d=zohomail.com; s=zohoarc; b=JI60mrx8u/T4xrzWtRTj2ekvIt5oiYL7WtfhQlQzwRI16RA/pVZQ5e6lodMktDSnSlt51Hfgd8R89BH8phsq/1rln0j1OD0TgQWb6SuZviQ0Oaku4TiBcGf/AiK4+piFzHCErKC67JY+K9NUDQWHJXtSWtGkhgPrPY9jIPBQBHU= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1611838558; h=Content-Type:Content-Transfer-Encoding:Cc:Date:From:List-Subscribe:List-Post:List-Id:List-Help:List-Unsubscribe:MIME-Version:Message-ID:Sender:Subject:To; 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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=cKLMOQl3QM9Mishfg+0O7Eezt5 tWRwm/N6Em/BWV+9gD19oZgOLHElxqIDC3WRe/JxIRWhq1VDSv1wlFIPwrD0tvSlCcatAOFhsLKBL 3UzxCH3Wb0mw6AAACZRCw7pK8kTDvZjvh/ztxI2d3VDX579/cuAeCnaVcICKx8OgAZpE=; 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=20Pau=20Monn=C3=A9?= , Jens Axboe , Dongli Zhang Subject: [PATCH] xen-blkback: fix compatibility bug with single page rings Date: Thu, 28 Jan 2021 12:55:28 +0000 Message-Id: <20210128125528.11695-1-paul@xen.org> X-Mailer: git-send-email 2.17.1 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-ZohoMail-DKIM: pass (identity @xen.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 =3D 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 inconsist= ent xenstore 'ring-page-order' set by malicious blkfront") Signed-off-by: Paul Durrant --- Cc: Konrad Rzeszutek Wilk Cc: "Roger Pau Monn=C3=A9" Cc: Jens Axboe Cc: Dongli Zhang v2: - Remove now-spurious error path special-case when nr_grefs =3D=3D 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 { =20 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 =3D 0; i < nr_grefs; i++) { char ring_ref_name[RINGREF_NAME_LEN]; =20 - 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 !=3D 0); + snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref"); + } + err =3D xenbus_scanf(XBT_NIL, dir, ring_ref_name, "%u", &ring_ref[i]); =20 if (err !=3D 1) { - if (nr_grefs =3D=3D 1) - break; - err =3D -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) } } =20 - if (err !=3D 1) { - WARN_ON(nr_grefs !=3D 1); - - err =3D xenbus_scanf(XBT_NIL, dir, "ring-ref", "%u", - &ring_ref[0]); - if (err !=3D 1) { - err =3D -EINVAL; - xenbus_dev_fatal(dev, err, "reading %s/ring-ref", dir); - return err; - } - } - err =3D -ENOMEM; for (i =3D 0; i < nr_grefs * XEN_BLKIF_REQS_PER_PAGE; i++) { req =3D 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" : ""); =20 - ring_page_order =3D xenbus_read_unsigned(dev->otherend, - "ring-page-order", 0); - - if (ring_page_order > xen_blkif_max_ring_order) { + err =3D xenbus_scanf(XBT_NIL, dev->otherend, "ring-page-order", "%u", + &ring_page_order); + if (err !=3D 1) { + blkif->nr_ring_pages =3D 1; + blkif->multi_ref =3D false; + } else if (ring_page_order <=3D xen_blkif_max_ring_order) { + blkif->nr_ring_pages =3D 1 << ring_page_order; + blkif->multi_ref =3D true; + } else { err =3D -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; } =20 - blkif->nr_ring_pages =3D 1 << ring_page_order; - if (blkif->nr_rings =3D=3D 1) return read_per_ring_refs(&blkif->rings[0], dev->otherend); else { --=20 2.17.1