Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752073AbbHLUzv (ORCPT ); Wed, 12 Aug 2015 16:55:51 -0400 Received: from smtp45.i.mail.ru ([94.100.177.105]:37210 "EHLO smtp45.i.mail.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751712AbbHLUzs (ORCPT ); Wed, 12 Aug 2015 16:55:48 -0400 Subject: Re: [regression] x86/signal/64: Fix SS handling for signals delivered to 64-bit programs breaks dosemu To: Andy Lutomirski References: <55CA90B4.2010205@list.ru> <55CAFD9F.2070001@list.ru> <55CB7BAE.9090503@list.ru> <55CB9697.1050602@list.ru> <55CBA4CE.1040108@list.ru> <55CBA909.3020306@list.ru> <55CBB053.7050803@list.ru> Cc: X86 ML , Linux kernel From: Stas Sergeev Message-ID: <55CBB2CC.9090600@list.ru> Date: Wed, 12 Aug 2015 23:55:40 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-Mras: Ok Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3342 Lines: 62 12.08.2015 23:47, Andy Lutomirski пишет: > On Wed, Aug 12, 2015 at 1:45 PM, Stas Sergeev wrote: >> 12.08.2015 23:28, Andy Lutomirski пишет: >> >>> On Wed, Aug 12, 2015 at 1:14 PM, Stas Sergeev wrote: >>>> 12.08.2015 23:01, Andy Lutomirski пишет: >>>>> On Wed, Aug 12, 2015 at 12:55 PM, Stas Sergeev wrote: >>>>>> 12.08.2015 22:20, Andy Lutomirski пишет: >>>>>>> current kernels, it stays switched. If we change this, it won't stay >>>>>>> switched. Even ignoring old ABI, it's not really clear to me what the >>>>>>> right thing to do is. >>>>>> There can be the following cases: >>>>>> - switch_userspace_thread() switches fs to non-zero selector >>>>>> - switch_userspace_thread() switches the fs base via syscall >>>>>> - switch_userspace_thread() switches fs in sigcontext >>>>>> - switch_userspace_thread() switches fs_base in sigcontext (???) >>>>>> What exactly case do you have in mind? >>>>>> I'd say, the way x86_32 is doing things - is good, but the >>>>>> bases... perhaps, in ideal world, they should be a part of >>>>>> the sigcontext as well? >>>>> Any of the above. What do you want the kernel to do, and how does the >>>>> kernel know you want to do that? The kernel has to pick *some* >>>>> semantics here. >>>> Assuming the bases are made the part of a sigcontext, >>>> I'd say there would be no ambiguities remained at all: >>>> whatever you change in a sigcontext, will be "applied" by >>>> the sigreturn(). Whatever you put in the registers >>>> (either segregs or MSRs), is valid until sigreturn(), then >>>> forgotten forever. >>>> The mess only comes in when some things are part of >>>> sigcontext and some are not. But if you have _all_ things >>>> accessable in sigcontext, then the user has a way of expressing >>>> his needs very clearly: he'll either touch sigcontext or direct >>>> values, depending on what he need. >>>> >>>> Is this right? >>> Maybe, except that doing this might break existing code (Wine and Java >>> come to mind). I'm not really sure. >> Yes, but that's why I was talking about some new >> flag. Maybe a new sigaction() flag? Or something else that >> will allow the user to request explicitly the new handling >> where the things are all switched by the kernel. Then >> the old programs that don't use that flag, will remain >> unaffected. I realize this may be a lot of work... But please >> note that there will be no more a chance like this one, >> when things are already badly broken. :) > I think that, with my patch, we get the best of both worlds. We keep > the old behavior in cases where it would work, and we switch to the > new behavior in cases where the old behavior would result in killing > the task. But I mean also fs/TLS. There is a chance now to fix things for good, all at once. :) With such an ss patch applied to stable, there will be no more such a chance ever. What's your opinion on the possibility of fixing the TLS problem? Also I am not sure about the sigreturn()'s detection: is it a subject of the subsequent patch, or you dropped an idea? -- 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/