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: 558993 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [IPv6:2001:4830:134:3::11]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 364E31401AD for ; Sat, 19 Dec 2015 04:03:39 +1100 (AEDT) Received: from localhost ([::1]:33812 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a9yRM-0004q6-Tb for incoming@patchwork.ozlabs.org; Fri, 18 Dec 2015 12:03:36 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33275) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a9wno-0002VU-46 for qemu-devel@nongnu.org; Fri, 18 Dec 2015 10:18:40 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1a9wnj-0006nY-7g for qemu-devel@nongnu.org; Fri, 18 Dec 2015 10:18:40 -0500 Received: from smtp02.citrix.com ([66.165.176.63]:22471) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a9wnj-0006nT-3O; Fri, 18 Dec 2015 10:18:35 -0500 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 X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 66.165.176.63 Cc: qemu-stable@nongnu.org, xen-devel@lists.xensource.com, qemu-devel@nongnu.org, stefano.stabellini@eu.citrix.com Subject: [Qemu-devel] [PULL 2/2] xenfb: avoid reading twice the same fields from the shared page X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org 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;