From patchwork Wed Apr 1 16:16:43 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 228351 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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, 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 E16DCC2D0F0 for ; Wed, 1 Apr 2020 16:50:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9534720787 for ; Wed, 1 Apr 2020 16:50:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585759826; bh=bL7lnl2GqFhAGBZo2e7fJxDHlZSiBOzMDk+Ou/OCTqY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=xf+X175LuN/N02EC0iYzMOembYkGyabe2M6UPsjhuXbc4cX4B1rOH2dqESFO/dMVz bu5jFhKI5PkCEkWPjqlVDMZlHo/6sqo3LQQbY8rCg9igK6efZWj+5UAMJXdEtK9SXB K5bxf7VXZq88vpNp55EqvuXt7hIxpwqU5GnLfv3s= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389301AbgDAQkR (ORCPT ); Wed, 1 Apr 2020 12:40:17 -0400 Received: from mail.kernel.org ([198.145.29.99]:40478 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389289AbgDAQkR (ORCPT ); Wed, 1 Apr 2020 12:40:17 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A438420658; Wed, 1 Apr 2020 16:40:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585759216; bh=bL7lnl2GqFhAGBZo2e7fJxDHlZSiBOzMDk+Ou/OCTqY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=h6vP3wlI197aTSE/Bfx9IQvxebnkiYBX+KxASazdl4Vyfrc8hIM/mugLubuyeTg5B vICYvn//Yc5pmjMqN7zqtxjwp0pjoAYWx4xUiY2lwtj8j9TYwy4MZVY5Ccebg/eMdJ VgGZwAJMfgsH7rv21sJfCeTqYcxDF791/FoK0nGw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Dongli Zhang , Julien Grall , Boris Ostrovsky , Sasha Levin Subject: [PATCH 4.14 011/148] xenbus: req->body should be updated before req->state Date: Wed, 1 Apr 2020 18:16:43 +0200 Message-Id: <20200401161553.296913900@linuxfoundation.org> X-Mailer: git-send-email 2.26.0 In-Reply-To: <20200401161552.245876366@linuxfoundation.org> References: <20200401161552.245876366@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Dongli Zhang [ Upstream commit 1b6a51e86cce38cf4d48ce9c242120283ae2f603 ] The req->body should be updated before req->state is updated and the order should be guaranteed by a barrier. Otherwise, read_reply() might return req->body = NULL. Below is sample callstack when the issue is reproduced on purpose by reordering the updates of req->body and req->state and adding delay in code between updates of req->state and req->body. [ 22.356105] general protection fault: 0000 [#1] SMP PTI [ 22.361185] CPU: 2 PID: 52 Comm: xenwatch Not tainted 5.5.0xen+ #6 [ 22.366727] Hardware name: Xen HVM domU, BIOS ... [ 22.372245] RIP: 0010:_parse_integer_fixup_radix+0x6/0x60 ... ... [ 22.392163] RSP: 0018:ffffb2d64023fdf0 EFLAGS: 00010246 [ 22.395933] RAX: 0000000000000000 RBX: 75746e7562755f6d RCX: 0000000000000000 [ 22.400871] RDX: 0000000000000000 RSI: ffffb2d64023fdfc RDI: 75746e7562755f6d [ 22.405874] RBP: 0000000000000000 R08: 00000000000001e8 R09: 0000000000cdcdcd [ 22.410945] R10: ffffb2d6402ffe00 R11: ffff9d95395eaeb0 R12: ffff9d9535935000 [ 22.417613] R13: ffff9d9526d4a000 R14: ffff9d9526f4f340 R15: ffff9d9537654000 [ 22.423726] FS: 0000000000000000(0000) GS:ffff9d953bc80000(0000) knlGS:0000000000000000 [ 22.429898] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 22.434342] CR2: 000000c4206a9000 CR3: 00000001ea3fc002 CR4: 00000000001606e0 [ 22.439645] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 22.444941] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 22.450342] Call Trace: [ 22.452509] simple_strtoull+0x27/0x70 [ 22.455572] xenbus_transaction_start+0x31/0x50 [ 22.459104] netback_changed+0x76c/0xcc1 [xen_netfront] [ 22.463279] ? find_watch+0x40/0x40 [ 22.466156] xenwatch_thread+0xb4/0x150 [ 22.469309] ? wait_woken+0x80/0x80 [ 22.472198] kthread+0x10e/0x130 [ 22.474925] ? kthread_park+0x80/0x80 [ 22.477946] ret_from_fork+0x35/0x40 [ 22.480968] Modules linked in: xen_kbdfront xen_fbfront(+) xen_netfront xen_blkfront [ 22.486783] ---[ end trace a9222030a747c3f7 ]--- [ 22.490424] RIP: 0010:_parse_integer_fixup_radix+0x6/0x60 The virt_rmb() is added in the 'true' path of test_reply(). The "while" is changed to "do while" so that test_reply() is used as a read memory barrier. Signed-off-by: Dongli Zhang Link: https://lore.kernel.org/r/20200303221423.21962-1-dongli.zhang@oracle.com Reviewed-by: Julien Grall Signed-off-by: Boris Ostrovsky Signed-off-by: Sasha Levin --- drivers/xen/xenbus/xenbus_comms.c | 2 ++ drivers/xen/xenbus/xenbus_xs.c | 9 ++++++--- 2 files changed, 8 insertions(+), 3 deletions(-) diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c index d239fc3c5e3de..852ed161fc2a7 100644 --- a/drivers/xen/xenbus/xenbus_comms.c +++ b/drivers/xen/xenbus/xenbus_comms.c @@ -313,6 +313,8 @@ static int process_msg(void) req->msg.type = state.msg.type; req->msg.len = state.msg.len; req->body = state.body; + /* write body, then update state */ + virt_wmb(); req->state = xb_req_state_got_reply; req->cb(req); } else diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c index 3f3b29398ab8e..b609c6e08796e 100644 --- a/drivers/xen/xenbus/xenbus_xs.c +++ b/drivers/xen/xenbus/xenbus_xs.c @@ -188,8 +188,11 @@ static bool xenbus_ok(void) static bool test_reply(struct xb_req_data *req) { - if (req->state == xb_req_state_got_reply || !xenbus_ok()) + if (req->state == xb_req_state_got_reply || !xenbus_ok()) { + /* read req->state before all other fields */ + virt_rmb(); return true; + } /* Make sure to reread req->state each time. */ barrier(); @@ -199,7 +202,7 @@ static bool test_reply(struct xb_req_data *req) static void *read_reply(struct xb_req_data *req) { - while (req->state != xb_req_state_got_reply) { + do { wait_event(req->wq, test_reply(req)); if (!xenbus_ok()) @@ -213,7 +216,7 @@ static void *read_reply(struct xb_req_data *req) if (req->err) return ERR_PTR(req->err); - } + } while (req->state != xb_req_state_got_reply); return req->body; }