From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754200AbcEZPTN (ORCPT ); Thu, 26 May 2016 11:19:13 -0400 Received: from foss.arm.com ([217.140.101.70]:40225 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753643AbcEZPTK (ORCPT ); Thu, 26 May 2016 11:19:10 -0400 Date: Thu, 26 May 2016 16:19:02 +0100 From: Catalin Marinas To: Szabolcs Nagy Cc: David Miller , nd@arm.com, arnd@arndb.de, ynorov@caviumnetworks.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, libc-alpha@sourceware.org, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, pinskia@gmail.com, broonie@kernel.org, joseph@codesourcery.com, christoph.muellner@theobroma-systems.com, bamvor.zhangjian@huawei.com, klimov.linux@gmail.com, Nathan_Lynch@mentor.com, agraf@suse.de, Prasun.Kapoor@caviumnetworks.com, kilobyte@angband.pl, geert@linux-m68k.org, philipp.tomsich@theobroma-systems.com Subject: Re: [PATCH 01/23] all: syscall wrappers: add documentation Message-ID: <20160526151902.GC7456@e104818-lin.cambridge.arm.com> References: <6293194.tGy03QJ9ME@wuerfel> <20160525.135039.244098606649448826.davem@davemloft.net> <6407614.fdv5XFSBue@wuerfel> <20160525.142821.1719403997976778673.davem@davemloft.net> <20160526142057.GA7456@e104818-lin.cambridge.arm.com> <57470D19.2000501@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <57470D19.2000501@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 26, 2016 at 03:50:01PM +0100, Szabolcs Nagy wrote: > On 26/05/16 15:20, Catalin Marinas wrote: > > While writing the above, I realised the current ILP32 patches still miss > > on converting pointers passed from user space (unless I got myself > > confused in macros). The new __SC_WRAP() and COMPAT_SYSCALL_WRAPx() > > macros take care of zero or sign extension via __SC_COMPAT_CAST(). > > However, we have two more existing cases which I don't see covered: > > > > a) Native syscalls taking a pointer argument and invoked directly from > > ILP32. For example, sys_read() takes a pointer but I don't see any > > __SC_WRAP added by patch 5 > > > > b) Current compat syscalls taking a pointer argument. For example, > > compat_sys_vmsplice() gets the iov32 pointer and the compiler assumes > > it is a 64-bit variable. I don't see where the upper half is zeroed > > on x32 sign/zero extension is currently left to userspace, > which is difficult to deal with, (long long)arg does the > wrong thing for pointer args. I agree, I don't think we should leave sign/zero extension to user. We should do it in the kernel either in a way similar to s390 (specific __SC_COMPAT_CAST, __SC_DELOUSE) or by always zeroing the arguments upper half on kernel entry with a few additional wrappers (where we have 64-bit arguments or they require sign extension). The latter has the disadvantage of having to split 64-bit arguments in user space while the former adds more maintenance burden to the kernel. I can't comment on performance aspects without some real numbers. -- Catalin From mboxrd@z Thu Jan 1 00:00:00 1970 From: catalin.marinas@arm.com (Catalin Marinas) Date: Thu, 26 May 2016 16:19:02 +0100 Subject: [PATCH 01/23] all: syscall wrappers: add documentation In-Reply-To: <57470D19.2000501@arm.com> References: <6293194.tGy03QJ9ME@wuerfel> <20160525.135039.244098606649448826.davem@davemloft.net> <6407614.fdv5XFSBue@wuerfel> <20160525.142821.1719403997976778673.davem@davemloft.net> <20160526142057.GA7456@e104818-lin.cambridge.arm.com> <57470D19.2000501@arm.com> Message-ID: <20160526151902.GC7456@e104818-lin.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, May 26, 2016 at 03:50:01PM +0100, Szabolcs Nagy wrote: > On 26/05/16 15:20, Catalin Marinas wrote: > > While writing the above, I realised the current ILP32 patches still miss > > on converting pointers passed from user space (unless I got myself > > confused in macros). The new __SC_WRAP() and COMPAT_SYSCALL_WRAPx() > > macros take care of zero or sign extension via __SC_COMPAT_CAST(). > > However, we have two more existing cases which I don't see covered: > > > > a) Native syscalls taking a pointer argument and invoked directly from > > ILP32. For example, sys_read() takes a pointer but I don't see any > > __SC_WRAP added by patch 5 > > > > b) Current compat syscalls taking a pointer argument. For example, > > compat_sys_vmsplice() gets the iov32 pointer and the compiler assumes > > it is a 64-bit variable. I don't see where the upper half is zeroed > > on x32 sign/zero extension is currently left to userspace, > which is difficult to deal with, (long long)arg does the > wrong thing for pointer args. I agree, I don't think we should leave sign/zero extension to user. We should do it in the kernel either in a way similar to s390 (specific __SC_COMPAT_CAST, __SC_DELOUSE) or by always zeroing the arguments upper half on kernel entry with a few additional wrappers (where we have 64-bit arguments or they require sign extension). The latter has the disadvantage of having to split 64-bit arguments in user space while the former adds more maintenance burden to the kernel. I can't comment on performance aspects without some real numbers. -- Catalin