Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754014AbbBNLcM (ORCPT ); Sat, 14 Feb 2015 06:32:12 -0500 Received: from foss.arm.com ([217.140.101.70]:50386 "EHLO usa-sjc-mx-foss1.foss.arm.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753853AbbBNLcK (ORCPT ); Sat, 14 Feb 2015 06:32:10 -0500 X-Greylist: delayed 580 seconds by postgrey-1.27 at vger.kernel.org; Sat, 14 Feb 2015 06:32:09 EST Date: Sat, 14 Feb 2015 11:22:23 +0000 From: Catalin Marinas To: Chris Metcalf Cc: Bamvor Jian Zhang , linux-arch@vger.kernel.org, mpe@ellerman.id.au, benh@kernel.crashing.org, deller@gmx.de, "dingtianhong@huawei.com" , heiko.carstens@de.ibm.com, "linux-kernel@vger.kernel.org" , Will Deacon , jejb@parisc-linux.org, "lizefan@huawei.com" , paulus@samba.org, ralf@linux-mips.org, hpa@zytor.com, schwidefsky@de.ibm.com, tglx@linutronix.de, mingo@redhat.com, davem@davemloft.net, "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH] compat: Fix endian issue in union sigval Message-ID: <20150214112220.GB10246@MBP.local> References: <1423563011-12377-1-git-send-email-bamvor.zhangjian@huawei.com> <20150210122718.GC32052@e104818-lin.cambridge.arm.com> <54DB3B60.4050100@huawei.com> <20150211154054.GD9058@e104818-lin.cambridge.arm.com> <54DDAF2B.2070707@huawei.com> <20150213104455.GA3508@e104818-lin.cambridge.arm.com> <54DE730D.3090100@ezchip.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54DE730D.3090100@ezchip.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 Content-Length: 3257 Lines: 69 On Fri, Feb 13, 2015 at 04:56:29PM -0500, Chris Metcalf wrote: > On 2/13/2015 5:44 AM, Catalin Marinas wrote: > >On Fri, Feb 13, 2015 at 04:00:43PM +0800, Bamvor Jian Zhang wrote: > >>diff --git a/arch/arm64/kernel/signal32.c b/arch/arm64/kernel/signal32.c > >>index e299de396e9b..32601939a3c8 100644 > >>--- a/arch/arm64/kernel/signal32.c > >>+++ b/arch/arm64/kernel/signal32.c > >>@@ -154,8 +154,7 @@ int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from) > >> case __SI_TIMER: > >> err |= __put_user(from->si_tid, &to->si_tid); > >> err |= __put_user(from->si_overrun, &to->si_overrun); > >>- err |= __put_user((compat_uptr_t)(unsigned long)from->si_ptr, > >>- &to->si_ptr); > >>+ err |= __put_user(from->si_int, &to->si_int); > >> break; > >> case __SI_POLL: > >> err |= __put_user(from->si_band, &to->si_band); > >>@@ -184,7 +183,7 @@ int copy_siginfo_to_user32(compat_siginfo_t __user *to, const siginfo_t *from) > >> case __SI_MESGQ: /* But this is */ > >> err |= __put_user(from->si_pid, &to->si_pid); > >> err |= __put_user(from->si_uid, &to->si_uid); > >>- err |= __put_user((compat_uptr_t)(unsigned long)from->si_ptr, &to->si_ptr); > >>+ err |= __put_user(from->si_int, &to->si_int); > >> break; > >> case __SI_SYS: > >> err |= __put_user((compat_uptr_t)(unsigned long) > > I must be confused here, but I don't see that these do anything different. > > If we are writing 32 bits to to->si_ptr or to->si_int, either way the high 32 bits > are irrelevant. So whether we read it from from->si_ptr and massage the high bits, > or just read it from from->si_int as a straight-up 32-bit quantity, either way it > seems we should end up writing the same bits to userspace. > > I would understand the argument if we were overlaying the si_ptr/si_int union > from a kernel-side siginfo_t where si_ptr and si_int are different sizes > onto userspace, but it doesn't seem we ever do that. That's the problem, "from" above is a kernel siginfo_t while "to" is a compat_siginfo_t. The call paths go something like: 1. user populates sival_int compat_sigevent and invokes compat_sys_mq_notify() 2. kernel get_compat_sigevent() copies compat_sigevent into the native sigevent. compat and native sival_int are the same, no problem so far. The other half of 64-bit sival_ptr is zeroed by a memset in this function (this other half can be top or bottom, depending on endianness) 3. signal is about to be delivered to user via arch code. The compat_ptr(from->si_ptr) conversion always takes the least significant part of the native si_ptr. On big endian 64-bit, this is zero because get_compat_sigevent() populated the top part of si_ptr with si_int. So delivering such signals to compat user always sets si_int to 0. Little endian is fine. A similar example is sys_timer_create() which takes a sigevent argument. Maybe Bamvor has a test case. (btw, I'm off for a week, I'll follow up when I get back) -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/