From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [PATCH 08/11] signal/arm: Document conflicts with SI_USER and SIGFPE Date: Mon, 15 Jan 2018 14:12:26 -0600 Message-ID: <878tcyop91.fsf@xmission.com> References: <87373b6ghs.fsf@xmission.com> <20180112005940.23279-8-ebiederm@xmission.com> <20180115174947.GH17719@n2100.armlinux.org.uk> Mime-Version: 1.0 Content-Type: text/plain Return-path: Received: from out01.mta.xmission.com ([166.70.13.231]:42081 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750714AbeAOUNT (ORCPT ); Mon, 15 Jan 2018 15:13:19 -0500 In-Reply-To: <20180115174947.GH17719@n2100.armlinux.org.uk> (Russell King's message of "Mon, 15 Jan 2018 17:49:47 +0000") Sender: linux-arch-owner@vger.kernel.org List-ID: To: Russell King - ARM Linux Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Oleg Nesterov , linux-arm-kernel@lists.infradead.org, Al Viro Russell King - ARM Linux writes: > On Thu, Jan 11, 2018 at 06:59:37PM -0600, Eric W. Biederman wrote: >> 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 be reliably copied. > > So what do you suggest when none of the SIGFPE FPE_xxx codes match the > condition that "we don't know what happened" ? Raise a SIGKILL instead > maybe? We will have dumped the VFP state into the kernel log at this > point, things are pretty much fscked. > > It's probably an impossible condition unless the hardware has failed, > no one has knowingly reported getting such a dump in their kernel log, > so it's something that could very likely be changed in some way > without anyone noticing. It sounds like we have two equally valid possible solutions: 1) force_sig(SIGKILL, current); 2) Allocate a new FPE_xxx code in asm-generic/siginfo.h I believe the next available number is 15. If no one is going to notice this should be comparatively easy to fix. I just don't have the knowledge of arm to make the judgement myself. Eric