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 16045C2D0A3 for ; Fri, 6 Nov 2020 08:44:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8666820A8B for ; Fri, 6 Nov 2020 08:44:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726606AbgKFIod convert rfc822-to-8bit (ORCPT ); Fri, 6 Nov 2020 03:44:33 -0500 Received: from eu-smtp-delivery-151.mimecast.com ([207.82.80.151]:38225 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725830AbgKFIod (ORCPT ); Fri, 6 Nov 2020 03:44:33 -0500 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-68-jUwjDba8OY2VwwZx-KRtiA-1; Fri, 06 Nov 2020 08:44:27 +0000 X-MC-Unique: jUwjDba8OY2VwwZx-KRtiA-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; Fri, 6 Nov 2020 08:44:20 +0000 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; Fri, 6 Nov 2020 08:44:20 +0000 From: David Laight To: 'Jakub Kicinski' , Andrew Lunn CC: netdev , Nicolas Pitre , "Lee Jones" Subject: RE: [PATCH net-next v2 6/7] drivers: net: smc911x: Fix cast from pointer to integer of different size Thread-Topic: [PATCH net-next v2 6/7] drivers: net: smc911x: Fix cast from pointer to integer of different size Thread-Index: AQHWs8Wc9clo0WoJVE6rwm6TlnJJWam6x96A Date: Fri, 6 Nov 2020 08:44:20 +0000 Message-ID: References: <20201104154858.1247725-1-andrew@lunn.ch> <20201104154858.1247725-7-andrew@lunn.ch> <20201105144711.40a2f8f6@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> In-Reply-To: <20201105144711.40a2f8f6@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> 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: netdev@vger.kernel.org From: Jakub Kicinski > Sent: 05 November 2020 22:47 > > On Wed, 4 Nov 2020 16:48:57 +0100 Andrew Lunn wrote: > > - buf = (char*)((u32)skb->data & ~0x3); > > - len = (skb->len + 3 + ((u32)skb->data & 3)) & ~0x3; > > - cmdA = (((u32)skb->data & 0x3) << 16) | > > + offset = (unsigned long)skb->data & 3; > > + buf = skb->data - offset; > > + len = skb->len + offset; > > + cmdA = (offset << 16) | > > The len calculation is wrong, you trusted people on the mailing list > too much ;) I misread what the comment-free convoluted code was doing.... Clearly it is rounding the base address down to a multiple of 4 and passing the offset in cmdA. This is fine - but quite why the (I assume) hardware doesn't do this itself and just document that it does a 32bit read is another matter - the logic will be much the same and I doubt anything modern is that pushed for space. However rounding the length up to a multiple of 4 is buggy. If this is an ethernet chipset it must (honest) be able to send frames that don't end on a 4 byte boundary. So rounding up the length is very dubious. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)