From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from out03.mta.xmission.com ([166.70.13.233]:54072 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751764AbeBWAPv (ORCPT ); Thu, 22 Feb 2018 19:15:51 -0500 From: ebiederm@xmission.com (Eric W. Biederman) References: <87373b6ghs.fsf@xmission.com> <20180112005940.23279-4-ebiederm@xmission.com> <20180112222944.GA22642@ls3530.fritz.box> Date: Thu, 22 Feb 2018 18:15:16 -0600 In-Reply-To: <20180112222944.GA22642@ls3530.fritz.box> (Helge Deller's message of "Fri, 12 Jan 2018 23:29:44 +0100") Message-ID: <87fu5s4l4b.fsf@xmission.com> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [PATCH 04/11] signal/parisc: Document a conflict with SI_USER with SIGFPE Sender: linux-arch-owner@vger.kernel.org List-ID: To: Helge Deller Cc: linux-parisc@vger.kernel.org, James Bottomley , John David Anglin , linux-kernel@vger.kernel.org, Al Viro , Oleg Nesterov , linux-arch@vger.kernel.org Helge Deller writes: > * Eric W. Biederman : >> Setting si_code to 0 results in a userspace seeing an si_code of 0. >> This is the same si_code as SI_USER. Posix and common sense requires >> that SI_USER not be a signal specific si_code. As such this use of 0 >> for the si_code is a pretty horribly broken ABI. >> >> Further use of si_code == 0 guaranteed that copy_siginfo_to_user saw a >> value of __SI_KILL and now sees a value of SIL_KILL with the result >> that uid and pid fields are copied and which might copying the si_addr >> field by accident but certainly not by design. Making this a very >> flakey implementation. >> >> Utilizing FPE_FIXME siginfo_layout will now return SIL_FAULT and the >> appropriate fields will reliably be copied. >> >> This bug is 13 years old and parsic machines are no longer being built >> so I don't know if it possible or worth fixing it. But it is at least >> worth documenting this so other architectures don't make the same >> mistake. > > > I think we should fix it, even if we now break the ABI. > > It's about a "conditional trap" which needs to be handled by userspace. > I doubt there is any Linux code out which is utilizing this > parisc-specific trap. > > I'd suggest to add a new FPE trap si_code (e.g. FPE_CONDTRAP). > While at it, maybe we should include the already existing FPE_MDAOVF > from the frv architecture, so that arch/frv/include/uapi/asm/siginfo.h > can go completely. > > Suggested patch is below. > > I'm willing to test the patch below on the parisc architecture for a few > weeks. And it will break arch/x86/kernel/signal_compat.c which needs > looking at then too. Have you managed to test this change? I am sitting looking at another new FPE si_code and if this has been tested I figure FPE_CONDTRAP should get the next available FPE si_code and the other change should get the one that follows. Eric