Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755091AbcJLMzY (ORCPT ); Wed, 12 Oct 2016 08:55:24 -0400 Received: from mail.kernel.org ([198.145.29.136]:51116 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755440AbcJLMvo (ORCPT ); Wed, 12 Oct 2016 08:51:44 -0400 From: lizf@kernel.org To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, David Vrabel , Konrad Rzeszutek Wilk , Zefan Li Subject: [PATCH 3.4 092/125] xen: Add RING_COPY_REQUEST() Date: Wed, 12 Oct 2016 20:33:28 +0800 Message-Id: <1476275641-4697-92-git-send-email-lizf@kernel.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1476275600-4626-1-git-send-email-lizf@kernel.org> References: <1476275600-4626-1-git-send-email-lizf@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2033 Lines: 58 From: David Vrabel 3.4.113-rc1 review patch. If anyone has any objections, please let me know. ------------------ commit 454d5d882c7e412b840e3c99010fe81a9862f6fb upstream. Using RING_GET_REQUEST() on a shared ring is easy to use incorrectly (i.e., by not considering that the other end may alter the data in the shared ring while it is being inspected). Safe usage of a request generally requires taking a local copy. Provide a RING_COPY_REQUEST() macro to use instead of RING_GET_REQUEST() and an open-coded memcpy(). This takes care of ensuring that the copy is done correctly regardless of any possible compiler optimizations. Use a volatile source to prevent the compiler from reordering or omitting the copy. This is part of XSA155. Signed-off-by: David Vrabel Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: Zefan Li --- include/xen/interface/io/ring.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/include/xen/interface/io/ring.h b/include/xen/interface/io/ring.h index 7d28aff..7dc685b 100644 --- a/include/xen/interface/io/ring.h +++ b/include/xen/interface/io/ring.h @@ -181,6 +181,20 @@ struct __name##_back_ring { \ #define RING_GET_REQUEST(_r, _idx) \ (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].req)) +/* + * Get a local copy of a request. + * + * Use this in preference to RING_GET_REQUEST() so all processing is + * done on a local copy that cannot be modified by the other end. + * + * Note that https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 may cause this + * to be ineffective where _req is a struct which consists of only bitfields. + */ +#define RING_COPY_REQUEST(_r, _idx, _req) do { \ + /* Use volatile to force the copy into _req. */ \ + *(_req) = *(volatile typeof(_req))RING_GET_REQUEST(_r, _idx); \ +} while (0) + #define RING_GET_RESPONSE(_r, _idx) \ (&((_r)->sring->ring[((_idx) & (RING_SIZE(_r) - 1))].rsp)) -- 1.9.1