From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030346Ab2HWKnc (ORCPT ); Thu, 23 Aug 2012 06:43:32 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:42608 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030270Ab2HWKnZ (ORCPT ); Thu, 23 Aug 2012 06:43:25 -0400 Date: Thu, 23 Aug 2012 11:42:52 +0100 From: Catalin Marinas To: Arnd Bergmann Cc: Will Deacon , "linux-arch@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Jiri Kosina , "x86@kernel.org" , Martin Schwidefsky , Heiko Carstens , "David S. Miller" , Andi Kleen , "James E.J. Bottomley" , Ralf Baechle , Benjamin Herrenschmidt , Paul Mackerras Subject: Re: PER_LINUX32, Was: [PATCH v2 21/31] arm64: 32-bit (compat) applications support Message-ID: <20120823104252.GA7585@arm.com> References: <1344966752-16102-1-git-send-email-catalin.marinas@arm.com> <201208151434.05145.arnd@arndb.de> <20120816102808.GH31784@mudshark.cambridge.arm.com> <201208230646.31276.arnd@arndb.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <201208230646.31276.arnd@arndb.de> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 23, 2012 at 07:46:30AM +0100, Arnd Bergmann wrote: > On Thursday 16 August 2012, Will Deacon wrote: > > On Wed, Aug 15, 2012 at 03:34:04PM +0100, Arnd Bergmann wrote: > > > On Tuesday 14 August 2012, Catalin Marinas wrote: > > > > +asmlinkage int compat_sys_personality(compat_ulong_t personality) > > > > +{ > > > > + int ret; > > > > + > > > > + if (personality(current->personality) == PER_LINUX32 && > > > > + personality == PER_LINUX) > > > > + personality = PER_LINUX32; > > > > + ret = sys_personality(personality); > > > > + if (ret == PER_LINUX32) > > > > + ret = PER_LINUX; > > > > + return ret; > > > > +} > > > > > > Where did you get this from? > > > > > > You should not need compat_sys_personality, just call the native function. > > > > Hmm, but in that case an aarch32 application doing a personality(PER_LINUX) > > syscall will start seeing the wrong uname. > > Coming back at this topic, I noticed another issue. Jiri Kosina > has recently posted patches to fix this function in the other architectures > in order to mask out the other personality bits, which is a correct fix, > but the above function is odd for other reasons. > > * On MIPS, it is used only for compat tasks, like you have it above. > * On PA-RISC, it is used for native 32 bit tasks and for compat 32 bit tasks, > but not for native 64 bit ones. > * On IA64, it was used for compat tasks (support for which has since > been removed from the kernel), plus all 32 bit tasks would start with > PER_LINUX32. > * On PowerPC, Sparc and s390, it is used for native 64 bit tasks and for > compat 32 bit tasks, but not for native 32 bit ones. > * On Tile, it was never used. > * On x86_64, it used to be defined (copied from ia64) but not used > throughout the git history. > > The semantics of the function are also interesting: The intention seems > to be that to a compat task, PER_LINUX32 would appear as PER_LINUX. > The effect is that any process can set PER_LINUX32 but it can never > be unset except by a 64 bit MIPS or PA-RISC task. IMHO, it makes sense to keep the compat_sys_personality() as implemented above. You may want to start a chroot ARMv7 environment using "linux32" but don't want some 32-bit app calling personality(PER_LINUX) (as that's the default personality on an ARMv7 system) and unknowingly changing the personality that you wanted to enforce via "linux32". I agree with not setting the personality based on the ELF type, but that's different from the compat_sys_personality(). > Since x86_64 does not implement this behavior at all, I suspect that > there are now lots of things depending on not having it, while all > the other architectures might also have some (even predating the > x86_64 port) use cases that depend on depend on not being able to > observe PER_LINUX32 in 32 bit compat tasks. > > I think we should try to agree on how this is all supposed to work > and use common code, either put the ppc/sparc/s390 version into > sys_personality, or remove all of them and just do what x86 and tile > do, using the regular sys_personality for all tasks. Late topic for the KS :). I don't think we can move this behaviour to sys_personality. We may want to add a generic compat_sys_personality() if we agree on the above use-case. -- Catalin