From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933384AbcBZOfo (ORCPT ); Fri, 26 Feb 2016 09:35:44 -0500 Received: from mail-bl2on0078.outbound.protection.outlook.com ([65.55.169.78]:29136 "EHLO na01-bl2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932908AbcBZOfk (ORCPT ); Fri, 26 Feb 2016 09:35:40 -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: Fri, 26 Feb 2016 17:34:51 +0300 Message-ID: <1456497295-22991-2-git-send-email-ynorov@caviumnetworks.com> X-Mailer: git-send-email 2.5.0 In-Reply-To: <1456497295-22991-1-git-send-email-ynorov@caviumnetworks.com> References: <1456497295-22991-1-git-send-email-ynorov@caviumnetworks.com> MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [95.143.213.121] X-ClientProxiedBy: DB5PR02CA0007.eurprd02.prod.outlook.com (25.161.237.17) To BY2PR07MB613.namprd07.prod.outlook.com (10.141.222.144) X-Microsoft-Exchange-Diagnostics: 1;BY2PR07MB613;2:yWMEA0O3149tYe0D3OBwRx7G6rO/A0lpLiD077LEuj0HELB8l0tWRyx+vO3LrZcH2l5DSL55gJUdijMIwZ8GKN37Azoc6MrKwWVt4+QTlh2TKcX/dEcDUjY1ZpeTj56H3u7MKY3as9AVsbwB3FPYfA==;3:ChL3IpPZAqXrirCc89mm4z1h1TxR3HpBd+/iA7Jy/aZy31G+x9sGqwYsWYotiB35QqeLMsAO6uEFqN5hajAHEdZjJJBuoOcyCXR7NwseMDnIj+6TE4TzY7+9qBEFQpjH;25:vRFe6551UfUfwMneSWfx62T64TaW5cQ8VjD0NIDi2ZI8i40zXO9uMlcdRyt4oHbgr9HMJzbK4m3BRwgV6MP5ORviu5KYqt8m9ajnnBAPk7YEIOKPq8x99ueQeL6qVUfoNyoV4RP8DQ+Q3dOLYL7YYjgFT4DY78y4TUzWHHXWATmS0VBqtkQltMQy41HcEVNsIZkW5Mh83Dz/EARwWZm/ojf/5nxv1pHbcUFpVGmonXsC0+4kr6aaiq4AgyI8LDIJ//UlS8EGDuW8/DmXBxkYM7GREmdqA5qXBxl9B2QHqu7q1G/i27ghnfTxgvN1s6cGvjwfp0OAg0cNRkwZ/FJujg== X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:;SRVR:BY2PR07MB613; 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X-Microsoft-Exchange-Diagnostics: =?us-ascii?Q?1;BY2PR07MB613;23:XsZIrF9w7CYbnToQiYSmYzazhtZmhfIVVza2BFREiD?= =?us-ascii?Q?l4A6DplvjeXCBkqylHLc1lp2tsv4JUdi65P7lhGhoDziqwfnXtjXyTItazvu?= =?us-ascii?Q?GKeWmSiCHsWvqm5oa/K2wktbhcwLxmcp8n0pIJUW12pAPrxUvaN75BvX1OsM?= =?us-ascii?Q?qt8oNRh8G/5Dmv9uOLROa+ctqh898Orb+yMfYL2QRwR942OrT+Mh478c8LDm?= =?us-ascii?Q?nK3sr5WlcIack6JqGAcpxWW8+BKt+yYhbi5RPdpiDsqwRtx0tYoJgq+41rnt?= =?us-ascii?Q?Aob8S+EGnKhGdGkPb1lE8zSh5Wn3Vx6RCq2pH37IuI3OTBB35bXz0ugQg2cY?= =?us-ascii?Q?q0DqbTdq23p/bghqCDjQVjqRROP7OqEPU2xuniRzhcydZ63Wh14bnmU8WNdP?= =?us-ascii?Q?iqZhE8JelJ/I7xKANWWZTtTSjHwVqSQQ/Gr/jxmevKCRXsBhKO+wGEHEp6rL?= =?us-ascii?Q?7BZuaF2zKClsoVQ5OhhA08SgGCoXiI9LwxN1q0DQbVjOxhurWJw2Vuh2fq2y?= =?us-ascii?Q?Z0KTBPEbB7AeLlxwpFfpmeGTouDTnlQAA1Vx6ias9LhyXugM3fY0FBG9135r?= =?us-ascii?Q?St7OoyeRrBBSA5kvAKbmQxjJ8CnuphmxoWj5joymkJQyuo537I6rOkXR30P4?= =?us-ascii?Q?cjTiVCYmgBdrDruHcMxz2rw6d6Nnv9LN3/YB+k8twS0WbAdBKA1VC5muHXge?= =?us-ascii?Q?QofpYSfMyvbaEY0a51Audiji/KKdn2YZhdXBOFlhxGEval1/BaXZIBSGRJNb?= =?us-ascii?Q?hP2a4zEAhdDtk9qbBReZOBZVOkCvIsy7M/I9PBn8PwZjr2Cmp1jM0ZiulmZd?= =?us-ascii?Q?PcIdB1dwzsDZkwNY6rr2HNgodhMzLnI1KLjlH1kDhCxGbusBNg0vZdc+H4Nk?= =?us-ascii?Q?dUOm/Vbg5AeKtCTgY+NXRhYMhFC7WEi7oFlJuwuuqQK/SzaFLyO8Esw8B91A?= =?us-ascii?Q?spA2uhyJ1FFP8U4mvbCKz3j+3QXy04HkqeRwf7f5mlHgwYDdrFr8Z+bgFAB/?= =?us-ascii?Q?9XV4uQIDjzKAoemlwUnlyrf1CkknRfQqssEOlloW9HYRcE9hB5CK+I45AfSj?= =?us-ascii?Q?ozegXWBE4Ogzh2+ThY0pRdZ9cczo15ujg/NryVyjGhpUTSSQ=3D=3D?= X-Microsoft-Exchange-Diagnostics: 1;BY2PR07MB613;5:EWp63vemuWEaKMeKOm6EOgQt79dsey1JBcAiNVnnypwih7se+Y6GxomDoDfJAyuzWciBVbaqEboYlhD+IInF/U0/pXcjU6+ROLK9ez+W9AL0J86O2WBA6LcjRk9utJz4rPSS98PgDNGvjPPxhn/1cQ==;24:py/lFDN8rWmvrb5MLYjBmoxgVGc8MdznKfwWKuEKnJQdcRUq6/yWNPLQ82mC1PlgKtc+tnq+m8i4yprUm+YupROOZKyTIKgJj6IynCnJDbc= SpamDiagnosticOutput: 1:23 SpamDiagnosticMetadata: NSPM X-OriginatorOrg: caviumnetworks.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Feb 2016 14:35:36.0024 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY2PR07MB613 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..d02a6bd 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