From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52635) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ai3er-0003mk-Bh for qemu-devel@nongnu.org; Mon, 21 Mar 2016 13:30:29 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ai3en-0001bF-EZ for qemu-devel@nongnu.org; Mon, 21 Mar 2016 13:30:25 -0400 Received: from e37.co.us.ibm.com ([32.97.110.158]:47477) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ai3en-0001as-7C for qemu-devel@nongnu.org; Mon, 21 Mar 2016 13:30:21 -0400 Received: from localhost by e37.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 21 Mar 2016 11:30:20 -0600 From: Michael Roth Date: Mon, 21 Mar 2016 12:28:04 -0500 Message-Id: <1458581313-19045-7-git-send-email-mdroth@linux.vnet.ibm.com> In-Reply-To: <1458581313-19045-1-git-send-email-mdroth@linux.vnet.ibm.com> References: <1458581313-19045-1-git-send-email-mdroth@linux.vnet.ibm.com> Subject: [Qemu-devel] [PATCH 06/35] xenfb: avoid reading twice the same fields from the shared page List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Michael Roth , qemu-stable@nongnu.org, Stefano Stabellini From: Stefano Stabellini 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 (cherry picked from commit 7ea11bf376aea4bf8340eb363de9777c7f93e556) Signed-off-by: Michael Roth --- 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; -- 1.9.1