From patchwork Fri Dec 18 15:17:57 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stefano Stabellini X-Patchwork-Id: 7886491 Return-Path: X-Original-To: patchwork-xen-devel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id AFE55BEEE5 for ; Fri, 18 Dec 2015 15:20:41 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id E8225203AD for ; Fri, 18 Dec 2015 15:20:40 +0000 (UTC) Received: from lists.xen.org (lists.xenproject.org [50.57.142.19]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0936320416 for ; Fri, 18 Dec 2015 15:20:40 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=lists.xen.org) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1a9wnn-0006LA-4P; Fri, 18 Dec 2015 15:18:39 +0000 Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1a9wnl-0006KZ-Ox for xen-devel@lists.xensource.com; Fri, 18 Dec 2015 15:18:37 +0000 Received: from [193.109.254.147] by server-3.bemta-14.messagelabs.com id 39/88-25435-DC324765; Fri, 18 Dec 2015 15:18:37 +0000 X-Env-Sender: prvs=787e4ee0b=Stefano.Stabellini@citrix.com X-Msg-Ref: server-7.tower-27.messagelabs.com!1450451914!11974014!1 X-Originating-IP: [66.165.176.63] X-SpamReason: No, hits=0.0 required=7.0 tests=sa_preprocessor: VHJ1c3RlZCBJUDogNjYuMTY1LjE3Ni42MyA9PiAzMDYwNDg=\n, received_headers: No Received headers X-StarScan-Received: X-StarScan-Version: 7.35.1; banners=-,-,- X-VirusChecked: Checked Received: (qmail 12264 invoked from network); 18 Dec 2015 15:18:36 -0000 Received: from smtp02.citrix.com (HELO SMTP02.CITRIX.COM) (66.165.176.63) by server-7.tower-27.messagelabs.com with RC4-SHA encrypted SMTP; 18 Dec 2015 15:18:36 -0000 X-IronPort-AV: E=Sophos;i="5.20,446,1444694400"; d="scan'208";a="326284717" From: Stefano Stabellini To: Date: Fri, 18 Dec 2015 15:17:57 +0000 Message-ID: <1450451877-25157-2-git-send-email-stefano.stabellini@eu.citrix.com> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: References: MIME-Version: 1.0 X-DLP: MIA1 Cc: qemu-stable@nongnu.org, xen-devel@lists.xensource.com, qemu-devel@nongnu.org, stefano.stabellini@eu.citrix.com Subject: [Xen-devel] [PULL 2/2] xenfb: avoid reading twice the same fields from the shared page X-BeenThere: xen-devel@lists.xen.org X-Mailman-Version: 2.1.13 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org X-Spam-Status: No, score=-4.2 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_MED, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Reading twice the same field could give the guest an attack of opportunity. In the case of event->type, gcc could compile the switch statement into a jump table, effectively ending up reading the type field multiple times. This is part of XSA-155. Signed-off-by: Stefano Stabellini --- hw/display/xenfb.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/hw/display/xenfb.c b/hw/display/xenfb.c index 5e324ef..4e2a27a 100644 --- a/hw/display/xenfb.c +++ b/hw/display/xenfb.c @@ -784,18 +784,20 @@ static void xenfb_invalidate(void *opaque) static void xenfb_handle_events(struct XenFB *xenfb) { - uint32_t prod, cons; + uint32_t prod, cons, out_cons; struct xenfb_page *page = xenfb->c.page; prod = page->out_prod; - if (prod == page->out_cons) + out_cons = page->out_cons; + if (prod == out_cons) return; xen_rmb(); /* ensure we see ring contents up to prod */ - for (cons = page->out_cons; cons != prod; cons++) { + for (cons = out_cons; cons != prod; cons++) { union xenfb_out_event *event = &XENFB_OUT_RING_REF(page, cons); + uint8_t type = event->type; int x, y, w, h; - switch (event->type) { + switch (type) { case XENFB_TYPE_UPDATE: if (xenfb->up_count == UP_QUEUE) xenfb->up_fullscreen = 1;