From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758890AbcBXSf4 (ORCPT ); Wed, 24 Feb 2016 13:35:56 -0500 Received: from mail-bl2on0088.outbound.protection.outlook.com ([65.55.169.88]:61536 "EHLO na01-bl2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753232AbcBXSfx (ORCPT ); Wed, 24 Feb 2016 13:35:53 -0500 Authentication-Results: de.ibm.com; dkim=none (message not signed) header.d=none;de.ibm.com; dmarc=none action=none header.from=caviumnetworks.com; From: Yury Norov To: , , , , , , , CC: , , , , , , , , , Yury Norov Subject: [PATCH 1/5] all: syscall wrappers: add documentation Date: Wed, 24 Feb 2016 21:34:10 +0300 Message-ID: <1456338854-14901-2-git-send-email-ynorov@caviumnetworks.com> X-Mailer: git-send-email 2.5.0 In-Reply-To: <1456338854-14901-1-git-send-email-ynorov@caviumnetworks.com> References: <1456338854-14901-1-git-send-email-ynorov@caviumnetworks.com> MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [95.143.213.121] X-ClientProxiedBy: HE1PR01CA0023.eurprd01.prod.exchangelabs.com (25.163.2.161) To BLUPR07MB610.namprd07.prod.outlook.com (10.141.207.15) X-Microsoft-Exchange-Diagnostics: 1;BLUPR07MB610;2:/avoS/iJoEi6F413XmjoU8OmET2RW7koLWcfrQ8KvV59wM6ITZWzWRRJ7PMh5kTFJR3wH/Y/PLl/tgonTlc48WsWUrD6tUBqM96Wvz9dkz93+9Da0S6UT7vLs4VeK1Dvm1yoc7+TLwac4NE0+dGKkQ==;3:DgR6yGoA8Wsab1uZbNMLklbuAE49XIL1lvpWomTDNvmm5VqlOzpmjkJ3CE+qJi3O0zelZGeQTv9kd6xVX6LyoMu6NHnZl2v1DkP+ulGu8eIhzJtI5QtTyYcbZUM0vbcy;25:cih9xBQxyHFLyblQBHJoMt1KgHcsrBZp/SyMlL34C3zyerWLziPsqmrMWsdgWmQFY/VxxFnJjZuusEcuFylmJtXH6I/Z/Adx/ZdLfy36IL9FVj5wpWZBVPxh1SqqogA6HeJSkr94sMGklvbDqK8PRWLOd+yM+Q6LVrq8v4nEo+AhNGrTDEOHcK2Aok2D4Z2gFHDByz9dSyBt/9pdswGG+VnlNGZMZxetcB/VAly3bXe1fB+2bMQA3PKPb+jbY9siSNBBnN9XUw2DGlvV9mEwduCqXuSg6G3tlYLoLjPijYTS+OnpxptokMuO6WdGhwQ51D2mWOoPTg1pC+jyiFTqvg== X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:;SRVR:BLUPR07MB610; 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X-Microsoft-Exchange-Diagnostics: =?us-ascii?Q?1;BLUPR07MB610;23:oPatbPtEvC4jalFEtwIZa9YW9o08nUwG+oVTDoAnfS?= =?us-ascii?Q?a+G+X5ECRm8AKBFvFCaFGwFUY783AM8334LlDq+MaavWEmagsGdKVuxOiNJ5?= =?us-ascii?Q?agxxpb1mYnhk1qmfd0NajITsYi7zrfDCcAlFfpWOkUPbQSCFAtckX4Tmq580?= =?us-ascii?Q?MzAT5ifpTHb69XJdo58Lhg0MGbQRPLidQCGwPHCwZmpJ0rjsiQlq7NPCzw87?= =?us-ascii?Q?vbSBnm8CeL0cXKdZjMpbAoVT90QZGiU609kRsmVfWf2Q6gwj7cjJxZf2hYPi?= =?us-ascii?Q?p4EDKkWv6riUZV+JsSWbQBmdf5AZ53JHr4GMGq/AtbLlmq0eKKqvhJ/0z0S5?= =?us-ascii?Q?D0JzpVfy9POnen9r48kOZeN0q1s5qocvwoAkggIw029Hris1ryDoU8+hmM4g?= =?us-ascii?Q?tRFerEX6FgLPZrnYGdrvzS/t18mNDJ09MRgky2tvK0tpy6PBU3J0wpoRt2Uz?= =?us-ascii?Q?Vt/UTV9UfwldSPEwuZ+ZmaHOoGycIeFkLLqfRsZ8flVFbd3kLqaCoJaWExTq?= =?us-ascii?Q?Pju0PCLQG7HOnhK2VK6qXJKcZde0i3iikJ4ihFfgQLvLccFap4Va1fWZL1yN?= =?us-ascii?Q?Xcan/W6uJRyY1HqD2PrYkBfCEayPvvpUJCI8EnRE3d0VLG9NMY20IVmgnfdK?= =?us-ascii?Q?1o8eSvNqaqDzjmpFCsHgPEXuk7Kl5Le/14t6U3M8H3z1Zk/YJjz+zDOr3DIQ?= =?us-ascii?Q?+vWrnwIcZpUs3aEfp2ami2BkJK52paz+0gh7hjtyDYCG58wRyz6XtO/I/E8h?= =?us-ascii?Q?R+De4VR9lFxCXaLiXEzZtvpyrQ5XzYPbzvxc+qvqS/JoRtiMyOiPoUmasC2g?= =?us-ascii?Q?LiLSd3roP0yw1nfZCbveilC/ikcrx6UL2RgRMEX49L2coWGagbQtndFSgUQ6?= =?us-ascii?Q?85K3Pzxd+3HBOibhXkGXIfpZOePRkh5Swp23bJDLNenr+tqyHKoO7cOmDHu0?= =?us-ascii?Q?oo/9nbgr9xaurmmoSb/pTwFNCL/WYtRCSMXfbpggWkANrcO9LmHEz1xV+Bzh?= =?us-ascii?Q?HCqM3S1DC12wOOkvaCDGZ7hubATgJeAXQLvMtcgfTkBjj0jz1v4FCoOqeT5R?= =?us-ascii?Q?gwHng=3D?= X-Microsoft-Exchange-Diagnostics: 1;BLUPR07MB610;5:J9SNvY8HGBXunIyENcNwYINFDSn7X3Tlg6z7BVgU2QDsxANu0YdVygBnNs1LueiSuw7moqShjs5jT+JZIX8znUIzP12cjvNeeqeOtnZeATZNSCALtqe3KPxqHF+nZuuhtXXC1SspDIAb+SqrkbS8Zw==;24:qr0GBrlLzZzU2VtMazltNUCK2pL5d1XpQl10s2bbiJzBFYxOl+LHBQ34uX+DFRmRTWHKLjnrBVRo32DoMXjzMXdhW4cL6motOEgc8+0gLWw= SpamDiagnosticOutput: 1:23 SpamDiagnosticMetadata: NSPM X-OriginatorOrg: caviumnetworks.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 Feb 2016 18:35:50.8103 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-Transport-CrossTenantHeadersStamped: BLUPR07MB610 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Signed-off-by: Yury Norov --- Documentation/adding-syscalls.txt | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/Documentation/adding-syscalls.txt b/Documentation/adding-syscalls.txt index cc2d4ac..1db880c 100644 --- a/Documentation/adding-syscalls.txt +++ b/Documentation/adding-syscalls.txt @@ -341,6 +341,38 @@ To summarize, you need: - instance of __SC_COMP not __SYSCALL in include/uapi/asm-generic/unistd.h +Compatibility System Calls Wrappers +-------------------------------- + +Some architectures prevent 32-bit userspace from access to top halves of 64-bit +registers, but some not. It's not a problem if specific argument is the same +size in kernel and userspace. It also is not a problem if system call is already +handled by compatible routine. Otherwise we'd take care of it. Usually, glibc +and compiler handles register's top halve, but from kernel side, we cannot rely +on it, as malicious code may cause incorrect behaviour and/or security +vulnerabilities. + +For now, only s390 and arm64/ilp32 are affected. + +To clear that top halves, automatic wrappers are introduced. They clear all +required registers before passing control to regular syscall handler. + +If your architecture allows userspace code to access top halves of register, +you need to: + - enable COMPAT_WRAPPER in configuration file; + - declare: "#define __SC_WRAP(nr, sym) [nr] = compat_##sym,", just before + compatible syscall table declaration, if you use generic unistd; or + - declare compat wrappers manually, if you use non-generic syscall table. + The list of unsafe syscalls is in kernel/compat_wrapper. + +If you write new syscall, make sure, its arguments are the same size in both +64- and 32-bits modes. If no, and if there's no explicit compat version for +syscall handler, you need to: + - declare compat version prototype in 'include/linux/compat.h'; + - in 'include/uapi/asm-generic/unistd.h' declare syscall with macro '__SC_WRAP' + instead of '__SYSCALL'; + - add corresponding line to 'kernel/compat_wrapper.c' to let it generate wrapper. + Compatibility System Calls (x86) -------------------------------- -- 2.5.0