From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Mon, 23 Jun 2014 13:06:27 +0200 (CEST) Received: from mailapp01.imgtec.com ([195.59.15.196]:1264 "EHLO mailapp01.imgtec.com" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S6817546AbaFWLGXGL4nl (ORCPT ); Mon, 23 Jun 2014 13:06:23 +0200 Received: from KLMAIL01.kl.imgtec.org (unknown [192.168.5.35]) by Websense Email Security Gateway with ESMTPS id 5DD712FF58114; Mon, 23 Jun 2014 12:06:14 +0100 (IST) Received: from KLMAIL02.kl.imgtec.org (192.168.5.97) by KLMAIL01.kl.imgtec.org (192.168.5.35) with Microsoft SMTP Server (TLS) id 14.3.181.6; Mon, 23 Jun 2014 12:06:16 +0100 Received: from LEMAIL01.le.imgtec.org (192.168.152.62) by klmail02.kl.imgtec.org (192.168.5.97) with Microsoft SMTP Server (TLS) id 14.3.181.6; Mon, 23 Jun 2014 12:06:16 +0100 Received: from [192.168.154.28] (192.168.154.28) by LEMAIL01.le.imgtec.org (192.168.152.62) with Microsoft SMTP Server (TLS) id 14.3.174.1; Mon, 23 Jun 2014 12:06:15 +0100 Message-ID: <53A80A27.5090503@imgtec.com> Date: Mon, 23 Jun 2014 12:06:15 +0100 From: Markos Chandras User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: David Laight , "linux-mips@linux-mips.org" CC: "David S. Miller" , Daniel Borkmann , Alexei Starovoitov , "netdev@vger.kernel.org" Subject: Re: [PATCH 14/17] MIPS: bpf: Prevent kernel fall over for >=32bit shifts References: <1403516340-22997-1-git-send-email-markos.chandras@imgtec.com> <1403516340-22997-15-git-send-email-markos.chandras@imgtec.com> <063D6719AE5E284EB5DD2968C1650D6D1726096C@AcuExch.aculab.com> In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D1726096C@AcuExch.aculab.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [192.168.154.28] Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 40675 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: Markos.Chandras@imgtec.com Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips On 06/23/2014 10:44 AM, David Laight wrote: > From: Markos Chandras >> Remove BUG_ON() if the shift immediate is >=32 to avoid >> kernel crashes due to malicious user input. Since the micro-assembler >> will not allow an immediate greater or equal to 32, we will use the >> maximum value which is 31. This will do the correct thing on either 32- >> or 64-bit cores since no 64-bit instructions are being used in JIT. > > I'm not sure that bounding the shift to 31 bits 'is the correct thing'. > I'd have thought that emulating the large shift or masking the shift > to 5 bits are equally 'correct'. > > ... Hi David, Since we use 32-bit registers (or rather, we ignore the top 32bits on MIPS64), shifting >= 32 will always result to 0. Alexei suggested [1] to allow large shifts and emulate them, so this patch aims to do that by treating >=32 shift values as 31. Please tell me if I got this wrong. [1] http://www.linux-mips.org/archives/linux-mips/2014-06/msg00212.html -- markos