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=-4.0 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 D0B0BC433DF for ; Tue, 21 Jul 2020 08:32:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B749920B1F for ; Tue, 21 Jul 2020 08:32:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728557AbgGUIcu convert rfc822-to-8bit (ORCPT ); Tue, 21 Jul 2020 04:32:50 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:60884 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726521AbgGUIcu (ORCPT ); Tue, 21 Jul 2020 04:32:50 -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-128-woYkEPDyM0aJ7Kkq3MEOcA-1; Tue, 21 Jul 2020 09:32:46 +0100 X-MC-Unique: woYkEPDyM0aJ7Kkq3MEOcA-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; Tue, 21 Jul 2020 09:32:45 +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; Tue, 21 Jul 2020 09:32:45 +0100 From: David Laight To: 'Marcelo Ricardo Leitner' CC: "linux-sctp@vger.kernel.org" , "netdev@vger.kernel.org" , Neil Horman Subject: RE: Misaligned IPv6 addresses is SCTP socket options. Thread-Topic: Misaligned IPv6 addresses is SCTP socket options. Thread-Index: AdZeq3CoQr6UZTOvRHy9xmmfSyelxAAVoqqAAAzMZSA= Date: Tue, 21 Jul 2020 08:32:45 +0000 Message-ID: <5bf6c1d336284bf7bf0a3a32d5b64910@AcuMS.aculab.com> References: <20200721025517.GA3399@localhost.localdomain> In-Reply-To: <20200721025517.GA3399@localhost.localdomain> 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: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Marcelo Ricardo Leitner > Sent: 21 July 2020 03:55 > > On Mon, Jul 20, 2020 at 03:50:16PM +0000, David Laight wrote: > > Several of the structures in linux/uapi/linux/sctp.h are > > marked __attribute__((packed, aligned(4))). > > I don't think we can change that by now. It's bad, yes, but it's > exposed and, well, for a long time (since 2005). > > > > > I believe this was done so that the UAPI structure was the > > same on both 32 and 64bit systems. > > The 'natural' alignment is that of 'u64' - so would differ > > between 32 and 64 bit x86 cpus. > > > > There are two horrible issues here: > > > > 1) I believe the natural alignment of u64 is actually 8 > > bytes on some 32bit architectures. > > Not sure which? Try arm for starters. > > So the change would have broken binary compatibility > > for 32bit applications compiled before the alignment > > was added. > > If nobody complained in 15 years, that's probably not a problem. ;-) > > > > > 2) Inside the kernel the address of the structure member > > is 'blindly' passed through as if it were an aligned > > pointer. > > For instance I'm pretty sure is can get passed to > > inet_addr_is_any() (in net/core/utils.). > > Here it gets passed to memcmp(). > > gcc will inline the memcmp() and almost certainly use 64bit > > accesses. > > These will fault on architectures (like sparc64). > > For 2) here we should fix it by copying the data into a different > buffer, or something like that. At least on some architectures. I did wonder if the buffer could be read to 8n+4 aligned memory, but there are aligned 64bit items elsewhere. > That is happening on structs sctp_setpeerprim sctp_prim > sctp_paddrparams sctp_paddrinfo, right? > As they all use the pattern of having a sockaddr_storage after a s32. Not no mention sctp_assoc_stats.... Which is broken for 32bit binaries on x86 and sparc 64bit kernels. I think there is (there should be) a kernel type on 64bit systems that is 8 bytes with the alignment it would have on the corresponding 32bit architecture. If nothing else using alignof() on a structure containing a member of that type will give the 4 or 8 required to fix the code. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)