From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Metcalf Subject: Re: [PATCH] compat: Fix endian issue in union sigval Date: Tue, 24 Feb 2015 16:54:17 -0500 Message-ID: <54ECF309.3020509@ezchip.com> References: <1423563011-12377-1-git-send-email-bamvor.zhangjian@huawei.com> <20150210122718.GC32052@e104818-lin.cambridge.arm.com> <54DB3B60.4050100@huawei.com> <20150211154054.GD9058@e104818-lin.cambridge.arm.com> <54DDAF2B.2070707@huawei.com> <20150213104455.GA3508@e104818-lin.cambridge.arm.com> <54DE730D.3090100@ezchip.com> <20150214112220.GB10246@MBP.local> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20150214112220.GB10246@MBP.local> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Catalin Marinas Cc: linux-arch@vger.kernel.org, benh@kernel.crashing.org, davem@davemloft.net, mpe@ellerman.id.au, deller@gmx.de, hpa@zytor.com, heiko.carstens@de.ibm.com, "linux-kernel@vger.kernel.org" , Will Deacon , jejb@parisc-linux.org, "lizefan@huawei.com" , Bamvor Jian Zhang , ralf@linux-mips.org, "dingtianhong@huawei.com" , schwidefsky@de.ibm.com, paulus@samba.org, tglx@linutronix.de, mingo@redhat.com, "linux-arm-kernel@lists.infradead.org" List-Id: linux-arch.vger.kernel.org On 2/14/2015 6:22 AM, Catalin Marinas wrote: > 1. user populates sival_int compat_sigevent and invokes > compat_sys_mq_notify() > 2. kernel get_compat_sigevent() copies compat_sigevent into the native > sigevent. compat and native sival_int are the same, no problem so > far. The other half of 64-bit sival_ptr is zeroed by a memset in this > function (this other half can be top or bottom, depending on > endianness) > 3. signal is about to be delivered to user via arch code. The > compat_ptr(from->si_ptr) conversion always takes the least > significant part of the native si_ptr. On big endian 64-bit, this is > zero because get_compat_sigevent() populated the top part of si_ptr > with si_int. > > So delivering such signals to compat user always sets si_int to 0. > Little endian is fine. I looked at this again as I was getting ready to do a tile patch, and realized why tile and arm64 are different here: tile does a field-by-field copy in copy_siginfo_from_user32(), like parisc and s390. As a result, we initialize the 64-bit kernel si_ptr value by cast from the 32-bit user si_ptr value, rather than blindly writing into the lower-addressed half of the 64-bit sigval. As a result, I think I will leave the existing code alone, though unfortunately that leaves it somewhat unique in manipulating the si_ptr field directly. But I think the s390 and parisc copy_siginfo_from_user32 leave the high bits of si_ptr uninitialized, which also strikes me as a bad idea in general. -- Chris Metcalf, EZChip Semiconductor http://www.ezchip.com From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-am1on0055.outbound.protection.outlook.com ([157.56.112.55]:18828 "EHLO emea01-am1-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752492AbbBXV7t (ORCPT ); Tue, 24 Feb 2015 16:59:49 -0500 Message-ID: <54ECF309.3020509@ezchip.com> Date: Tue, 24 Feb 2015 16:54:17 -0500 From: Chris Metcalf MIME-Version: 1.0 Subject: Re: [PATCH] compat: Fix endian issue in union sigval References: <1423563011-12377-1-git-send-email-bamvor.zhangjian@huawei.com> <20150210122718.GC32052@e104818-lin.cambridge.arm.com> <54DB3B60.4050100@huawei.com> <20150211154054.GD9058@e104818-lin.cambridge.arm.com> <54DDAF2B.2070707@huawei.com> <20150213104455.GA3508@e104818-lin.cambridge.arm.com> <54DE730D.3090100@ezchip.com> <20150214112220.GB10246@MBP.local> In-Reply-To: <20150214112220.GB10246@MBP.local> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Catalin Marinas Cc: Bamvor Jian Zhang , linux-arch@vger.kernel.org, mpe@ellerman.id.au, benh@kernel.crashing.org, deller@gmx.de, "dingtianhong@huawei.com" , heiko.carstens@de.ibm.com, "linux-kernel@vger.kernel.org" , Will Deacon , jejb@parisc-linux.org, "lizefan@huawei.com" , paulus@samba.org, ralf@linux-mips.org, hpa@zytor.com, schwidefsky@de.ibm.com, tglx@linutronix.de, mingo@redhat.com, davem@davemloft.net, "linux-arm-kernel@lists.infradead.org" Message-ID: <20150224215417._Gg6nd9nH94rZdwQwMWnRSZG_gedt6YhM5aLawqpMZ4@z> On 2/14/2015 6:22 AM, Catalin Marinas wrote: > 1. user populates sival_int compat_sigevent and invokes > compat_sys_mq_notify() > 2. kernel get_compat_sigevent() copies compat_sigevent into the native > sigevent. compat and native sival_int are the same, no problem so > far. The other half of 64-bit sival_ptr is zeroed by a memset in this > function (this other half can be top or bottom, depending on > endianness) > 3. signal is about to be delivered to user via arch code. The > compat_ptr(from->si_ptr) conversion always takes the least > significant part of the native si_ptr. On big endian 64-bit, this is > zero because get_compat_sigevent() populated the top part of si_ptr > with si_int. > > So delivering such signals to compat user always sets si_int to 0. > Little endian is fine. I looked at this again as I was getting ready to do a tile patch, and realized why tile and arm64 are different here: tile does a field-by-field copy in copy_siginfo_from_user32(), like parisc and s390. As a result, we initialize the 64-bit kernel si_ptr value by cast from the 32-bit user si_ptr value, rather than blindly writing into the lower-addressed half of the 64-bit sigval. As a result, I think I will leave the existing code alone, though unfortunately that leaves it somewhat unique in manipulating the si_ptr field directly. But I think the s390 and parisc copy_siginfo_from_user32 leave the high bits of si_ptr uninitialized, which also strikes me as a bad idea in general. -- Chris Metcalf, EZChip Semiconductor http://www.ezchip.com