From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965328AbeALWaY (ORCPT + 1 other); Fri, 12 Jan 2018 17:30:24 -0500 Received: from mout.gmx.net ([212.227.17.21]:63644 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965212AbeALWaU (ORCPT ); Fri, 12 Jan 2018 17:30:20 -0500 Date: Fri, 12 Jan 2018 23:29:44 +0100 From: Helge Deller To: "Eric W. Biederman" , linux-parisc@vger.kernel.org, James Bottomley , John David Anglin Cc: linux-kernel@vger.kernel.org, Al Viro , Oleg Nesterov , linux-arch@vger.kernel.org Subject: Re: [PATCH 04/11] signal/parisc: Document a conflict with SI_USER with SIGFPE Message-ID: <20180112222944.GA22642@ls3530.fritz.box> References: <87373b6ghs.fsf@xmission.com> <20180112005940.23279-4-ebiederm@xmission.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180112005940.23279-4-ebiederm@xmission.com> User-Agent: Mutt/1.9.1 (2017-09-22) X-Provags-ID: V03:K0:eTFfv40SbxQ1MpBxmCRNGkP/TKUmUipgYYbwM24xiz5jlD1GGXZ mK1PI8nelEpJZQuFoNQZTHCbWO9PydMiPNTE8NPXPEvawxF5ZLDX6xbLTG2Ro0RHrWV4jwc zN4LLcYF41wzVxqIhPDyEyT1ohBb0EmwdVYUBLdtWIwQCBy6SQLkv/7mHAwwlV1C1zdu+jP jF+WRirIiAEn30LyP+y4g== X-UI-Out-Filterresults: notjunk:1;V01:K0:jlktHS8v+kA=:mxwpKsbttJYMQ3RiFOPfS4 y+fkY1aunkkM6vw1yFqEFX5q3UFX6h4WIWjasVi4M4IuvRy0HlrQx1YwrXH/FaC+pbRJ9cLgP gFMv3s9UvwZrDV5B31y9jClGzBpcx5iDaP3C80vDRZ0xtkYToNt4rQYOOg+gd/O4+n839xIGr F/Vuzp0/CAlAJn7h1pbkbzZFwhtOhz9RSrtOb/R7lA+P/QEMrCGeccOEHDN3IeS+xCVbGbkNb 0y1tkaIZCt9lHJsjPihRumukWkjmnmWrMafStm02ILP5FGMo9cnYz13w0EqoQYFwpssnjoBqy XY98M3w+K41XwtMwS8jlj5CKeE7Hdjw9O6n+JbCH1l7UJhletUU2/kfONiifNapaO+TDJeIeF OXLYJwpxmcdR9gtYNMx/97+4edGnjKvwar94JlvO4zoTEAUOFRSAInd3Brnyj5CfGX5unHB+H NyuYO68LqmcwBLVmVvApVbxSLO8rMiEn8IbXyxCuM3fXTQYWXhMnRDA1cBP70uuKlFsgYvPpL cJyLMrgHBuEmdfoaED0H5hB+MTXwHTSQQJqFa4mRgb+XtyWIK+ZVF58SZRWhA/FfYrr+PuBgo k2Aetcz+p1Lqfih+Ec+7TOowsmwIN1iwX9Z1FQ2A7tQemLlG13alWSAmzefz6MyUMU/rIWR5a PqkF1yuC1ZMzXcazJZ1Efrgjsmxe+n3IaaimP0XXWiImYgpbxAyhG59YHVjFgM6j6ld4RkFtx Wqs8Zd13p1VjX2dxog/u3evZOrn55Tqa5FwHazLf471l3og7SKgMHjY27a4kvl8FiVBAlxZYc 7CwBeWjNZByvUAPuwAUeJzG2UP6zA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: * 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. Thoughts? Helge [PATCH] parisc: Add FPE_CONDTRAP for conditional trap handling Posix and common sense requires that SI_USER not be a signal specific si_code. Thus add a new FPE_CONDTRAP si_code for conditional traps. Signed-off-by: Helge Deller diff --git a/arch/parisc/kernel/traps.c b/arch/parisc/kernel/traps.c index 8453724b8009..13702f0f5ba1 100644 --- a/arch/parisc/kernel/traps.c +++ b/arch/parisc/kernel/traps.c @@ -627,9 +627,9 @@ void notrace handle_interruption(int code, struct pt_regs *regs) on condition */ if(user_mode(regs)){ si.si_signo = SIGFPE; - /* Set to zero, and let the userspace app figure it out from - the insn pointed to by si_addr */ - si.si_code = 0; + /* Let userspace app figure out from the insn pointed + * to by si_addr */ + si.si_code = FPE_CONDTRAP; si.si_addr = (void __user *) regs->iaoq[0]; force_sig_info(SIGFPE, &si, current); return; diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h index e447283b8f52..2b759fe42142 100644 --- a/include/uapi/asm-generic/siginfo.h +++ b/include/uapi/asm-generic/siginfo.h @@ -193,7 +193,9 @@ typedef struct siginfo { #define FPE_FLTRES 6 /* floating point inexact result */ #define FPE_FLTINV 7 /* floating point invalid operation */ #define FPE_FLTSUB 8 /* subscript out of range */ -#define NSIGFPE 8 +#define FPE_MDAOVF 9 /* media overflow */ +#define FPE_CONDTRAP 10 /* trap on condition */ +#define NSIGFPE 10 /* * SIGSEGV si_codes