From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DFFD5C43603 for ; Wed, 18 Dec 2019 10:22:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B32C9218AC for ; Wed, 18 Dec 2019 10:22:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726774AbfLRKWa (ORCPT ); Wed, 18 Dec 2019 05:22:30 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:9344 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725930AbfLRKWa (ORCPT ); Wed, 18 Dec 2019 05:22:30 -0500 Received: from pps.filterd (m0098410.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id xBIAMTdg078220 for ; Wed, 18 Dec 2019 05:22:29 -0500 Received: from e06smtp02.uk.ibm.com (e06smtp02.uk.ibm.com [195.75.94.98]) by mx0a-001b2d01.pphosted.com with ESMTP id 2wycp34q1r-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Wed, 18 Dec 2019 05:22:28 -0500 Received: from localhost by e06smtp02.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 18 Dec 2019 10:22:06 -0000 Received: from b06wcsmtp001.portsmouth.uk.ibm.com (b06wcsmtp001.portsmouth.uk.ibm.com [9.149.105.160]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id xBIAM5od37421230 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 18 Dec 2019 10:22:05 GMT Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A6BEDA405F; Wed, 18 Dec 2019 10:22:05 +0000 (GMT) Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 537ABA405B; Wed, 18 Dec 2019 10:22:05 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.152.224.119]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 18 Dec 2019 10:22:05 +0000 (GMT) Subject: Re: READ_ONCE() + STACKPROTECTOR_STRONG == :/ (was Re: [GIT PULL] Please pull powerpc/linux.git powerpc-5.5-2 tag (topic/kasan-bitops)) To: Linus Torvalds , Will Deacon Cc: Peter Zijlstra , Michael Ellerman , dja@axtens.net, Linux Kernel Mailing List , linuxppc-dev@lists.ozlabs.org, Christophe Leroy , linux-arch , Mark Rutland , Segher Boessenkool , Arnd Bergmann References: <87blslei5o.fsf@mpe.ellerman.id.au> <20191206131650.GM2827@hirez.programming.kicks-ass.net> <875zimp0ay.fsf@mpe.ellerman.id.au> <20191212080105.GV2844@hirez.programming.kicks-ass.net> <20191212100756.GA11317@willie-the-truck> <20191212104610.GW2827@hirez.programming.kicks-ass.net> <20191212180634.GA19020@willie-the-truck> <20191212193401.GB19020@willie-the-truck> From: Christian Borntraeger Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 19121810-0008-0000-0000-0000034220C3 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19121810-0009-0000-0000-00004A6234FF Message-Id: X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,18.0.572 definitions=2019-12-18_02:2019-12-17,2019-12-18 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 mlxscore=0 malwarescore=0 spamscore=0 priorityscore=1501 bulkscore=0 clxscore=1015 adultscore=0 lowpriorityscore=0 suspectscore=0 mlxlogscore=999 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1910280000 definitions=main-1912180086 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12.12.19 21:49, Linus Torvalds wrote: > On Thu, Dec 12, 2019 at 11:34 AM Will Deacon wrote: >> >> The root of my concern in all of this, and what started me looking at it in >> the first place, is the interaction with 'typeof()'. Inheriting 'volatile' >> for a pointer means that local variables in macros declared using typeof() >> suddenly start generating *hideous* code, particularly when pointless stack >> spills get stackprotector all excited. > > Yeah, removing volatile can be a bit annoying. > > For the particular case of the bitops, though, it's not an issue. > Since you know the type there, you can just cast it. > > And if we had the rule that READ_ONCE() was an arithmetic type, you could do > > typeof(0+(*p)) __var; > > since you might as well get the integer promotion anyway (on the > non-volatile result). > > But that doesn't work with structures or unions, of course. We do have a READ_ONCE on the following union in s390 code. union ipte_control { unsigned long val; struct { unsigned long k : 1; unsigned long kh : 31; unsigned long kg : 32; }; }; In fact this one was the original failure case why we change ACCESS_ONCE. see arch/s390/kvm/gaccess.c