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=-0.8 required=3.0 tests=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 6297BC2D0E5 for ; Mon, 30 Mar 2020 15:54:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 37305205ED for ; Mon, 30 Mar 2020 15:54:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729735AbgC3Py1 convert rfc822-to-8bit (ORCPT ); Mon, 30 Mar 2020 11:54:27 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([146.101.78.151]:47850 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726497AbgC3Py0 (ORCPT ); Mon, 30 Mar 2020 11:54:26 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-87-ODMv5bv9P12XgKJf7O7OVA-1; Mon, 30 Mar 2020 16:54:23 +0100 X-MC-Unique: ODMv5bv9P12XgKJf7O7OVA-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Mon, 30 Mar 2020 16:54:22 +0100 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Mon, 30 Mar 2020 16:54:22 +0100 From: David Laight To: 'Al Viro' , Ingo Molnar CC: Linus Torvalds , Thomas Gleixner , "x86@kernel.org" , "linux-kernel@vger.kernel.org" , "Borislav Petkov" Subject: RE: [RFC][PATCH 01/22] x86 user stack frame reads: switch to explicit __get_user() Thread-Topic: [RFC][PATCH 01/22] x86 user stack frame reads: switch to explicit __get_user() Thread-Index: AQHWBfOGBuGXOsXgxk+vqOM7n5IKaahhSkVQ Date: Mon, 30 Mar 2020 15:54:22 +0000 Message-ID: <0c08c4e00e4e4965969a16410e4e15d1@AcuMS.aculab.com> References: <20200323183620.GD23230@ZenIV.linux.org.uk> <20200323183819.250124-1-viro@ZenIV.linux.org.uk> <20200328104857.GA93574@gmail.com> <20200328115936.GA23230@ZenIV.linux.org.uk> <20200329092602.GB93574@gmail.com> <20200329175735.GC23230@ZenIV.linux.org.uk> In-Reply-To: <20200329175735.GC23230@ZenIV.linux.org.uk> Accept-Language: en-GB, en-US Content-Language: 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 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Al Viro > Sent: 29 March 2020 18:58 ... > [*] IMO compat_alloc_user_space() should die; this "grab some space on > user stack, copy the 32bit data structure into 64bit equivalent there, > complete with pointer chasing and creating 64bit equivalents of everything > that's referenced from that struct, then call native ioctl, then do the > reverse conversion" is just plain wrong. That native ioctl is going to > bring the structures we'd constructed back into the kernel space and > work with them there; we might as well separate the function that work > with the copied struct (usually we do have those anyway) and call those > instead the native ioctl. And skip the damn "copy the structures we'd > built into temp allocation on user stack, then have it copied back" > part. We have relatively few callers, thankfully. I helped rip the same 'stackgap' code out of netbsd many years ago. No only was it being used for system call compatibility, but also for security checks and rewriting filenames. Completely hopeless in a threaded program. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)