From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3668FC433E4 for ; Fri, 26 Mar 2021 16:45:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F22FB61A36 for ; Fri, 26 Mar 2021 16:45:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230070AbhCZQpO convert rfc822-to-8bit (ORCPT ); Fri, 26 Mar 2021 12:45:14 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([185.58.86.151]:53579 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230304AbhCZQox (ORCPT ); Fri, 26 Mar 2021 12:44:53 -0400 Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-213-YTy4IFWENUi9fJgzzqBpKg-2; Fri, 26 Mar 2021 16:44:49 +0000 X-MC-Unique: YTy4IFWENUi9fJgzzqBpKg-2 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Fri, 26 Mar 2021 16:44:48 +0000 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.012; Fri, 26 Mar 2021 16:44:48 +0000 From: David Laight To: 'Al Viro' , Christoph Hellwig CC: "linux-arch@vger.kernel.org" , "linux-s390@vger.kernel.org" , "linux-parisc@vger.kernel.org" , Arnd Bergmann , Brian Gerst , "x86@kernel.org" , "linux-mips@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "Luis Chamberlain" , "Eric W. Biederman" , "sparclinux@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , "linux-arm-kernel@lists.infradead.org" Subject: RE: [PATCH 3/4] exec: simplify the compat syscall handling Thread-Topic: [PATCH 3/4] exec: simplify the compat syscall handling Thread-Index: AQHXIlr1GfPxLRNSxkCVNQRYzf6AcKqWeGLg Date: Fri, 26 Mar 2021 16:44:48 +0000 Message-ID: References: <20210326143831.1550030-1-hch@lst.de> <20210326143831.1550030-4-hch@lst.de> In-Reply-To: Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-parisc@vger.kernel.org From: Al Viro > Sent: 26 March 2021 16:12 > > On Fri, Mar 26, 2021 at 03:38:30PM +0100, Christoph Hellwig wrote: > > > +static const char __user * > > +get_user_arg_ptr(const char __user *const __user *argv, int nr) > > { > > + if (in_compat_syscall()) { > > + const compat_uptr_t __user *compat_argv = > > + compat_ptr((unsigned long)argv); > > compat_uptr_t compat; > > > > + if (get_user(compat, compat_argv + nr)) > > return ERR_PTR(-EFAULT); > > return compat_ptr(compat); > > + } else { > > + const char __user *native; > > > > + if (get_user(native, argv + nr)) > > + return ERR_PTR(-EFAULT); > > + return native; > > + } > > } > > Yecchhh.... So you have in_compat_syscall() called again and again, for > each argument in the list? I agree that current version is fucking ugly, > but I really hate that approach ;-/ Especially since in_compat_syscall() isn't entirely trivial on x86-64. Probably all in the noise for 'exec', but all the bits do add up. You may not want separate get_user() on some architectures either. The user_access_begin/end aren't cheap. OTOH if you call copy_from_user() you get hit by the stupid additional costs of 'user copy hardening'. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)