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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 B1F52C2BA83 for ; Thu, 13 Feb 2020 18:23:36 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 508BB21734 for ; Thu, 13 Feb 2020 18:23:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 508BB21734 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.ibm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:57670 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j2J9D-00015N-BK for qemu-devel@archiver.kernel.org; Thu, 13 Feb 2020 13:23:35 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:43238) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1j2Ioi-0007xA-K4 for qemu-devel@nongnu.org; Thu, 13 Feb 2020 13:02:25 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1j2Iof-0004YJ-JW for qemu-devel@nongnu.org; Thu, 13 Feb 2020 13:02:23 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:34002) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1j2Iof-0004TF-Ak; Thu, 13 Feb 2020 13:02:21 -0500 Received: from pps.filterd (m0098399.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 01DHniZP077250; Thu, 13 Feb 2020 13:02:19 -0500 Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com with ESMTP id 2y4j86s20d-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 13 Feb 2020 13:02:18 -0500 Received: from m0098399.ppops.net (m0098399.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.36/8.16.0.36) with SMTP id 01DHnrUl077686; Thu, 13 Feb 2020 13:02:17 -0500 Received: from ppma01dal.us.ibm.com (83.d6.3fa9.ip4.static.sl-reverse.com [169.63.214.131]) by mx0a-001b2d01.pphosted.com with ESMTP id 2y4j86s1yw-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 13 Feb 2020 13:02:17 -0500 Received: from pps.filterd (ppma01dal.us.ibm.com [127.0.0.1]) by ppma01dal.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id 01DI0Zit011024; Thu, 13 Feb 2020 18:02:16 GMT Received: from b03cxnp07028.gho.boulder.ibm.com (b03cxnp07028.gho.boulder.ibm.com [9.17.130.15]) by ppma01dal.us.ibm.com with ESMTP id 2y5bc000d1-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 13 Feb 2020 18:02:16 +0000 Received: from b03ledav001.gho.boulder.ibm.com (b03ledav001.gho.boulder.ibm.com [9.17.130.232]) by b03cxnp07028.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 01DI2Fw319726724 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 13 Feb 2020 18:02:15 GMT Received: from b03ledav001.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6E1CD6E050; Thu, 13 Feb 2020 18:02:15 +0000 (GMT) Received: from b03ledav001.gho.boulder.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 109176E052; Thu, 13 Feb 2020 18:02:14 +0000 (GMT) Received: from [9.60.75.232] (unknown [9.60.75.232]) by b03ledav001.gho.boulder.ibm.com (Postfix) with ESMTP; Thu, 13 Feb 2020 18:02:14 +0000 (GMT) Subject: Re: [PATCH] pc-bios/s390x: Pack ResetInfo struct To: Christian Borntraeger , qemu-devel@nongnu.org, qemu-s390x@nongnu.org, cohuck@redhat.com References: <20200205182126.13010-1-jjherne@linux.ibm.com> From: "Jason J. Herne" Organization: IBM Message-ID: Date: Thu, 13 Feb 2020 13:02:14 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138, 18.0.572 definitions=2020-02-13_06:2020-02-12, 2020-02-13 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 bulkscore=0 phishscore=0 priorityscore=1501 lowpriorityscore=0 mlxscore=0 impostorscore=0 malwarescore=0 spamscore=0 mlxlogscore=999 clxscore=1015 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002130127 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x [generic] X-Received-From: 148.163.156.1 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: jjherne@linux.ibm.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2/6/20 5:09 AM, Christian Borntraeger wrote: > > > On 05.02.20 19:21, Jason J. Herne wrote: >> This fixes vfio-ccw when booting non-Linux operating systems. Without this >> struct being packed, a few extra bytes of low core memory get overwritten when >> we assign a value to memory address 0 in jump_to_IPL_2. This is enough to >> cause some non-Linux OSes of fail when booting. >> >> The problem was introduced by: >> 5c6f0d5f46a77d77 "pc-bios/s390x: Fix reset psw mask". >> >> The fix is to pack the struct thereby removing the 4 bytes of padding that get >> added at the end, likely to allow an array of these structs to naturally align >> on an 8-byte boundary. >> >> Fixes: 5c6f0d5f46a7 ("pc-bios/s390x: Fix reset psw mask") >> CC: Janosch Frank >> Signed-off-by: Jason J. Herne >> --- >> pc-bios/s390-ccw/jump2ipl.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c >> index da13c43cc0..1e9eaa037f 100644 >> --- a/pc-bios/s390-ccw/jump2ipl.c >> +++ b/pc-bios/s390-ccw/jump2ipl.c >> @@ -18,7 +18,7 @@ >> typedef struct ResetInfo { >> uint64_t ipl_psw; >> uint32_t ipl_continue; >> -} ResetInfo; >> +} __attribute__((packed)) ResetInfo; >> >> static ResetInfo save; > > Just looked into that. > > We do save the old content in "save" and restore the old memory content. > > static void jump_to_IPL_2(void) > { > ResetInfo *current = 0; > > void (*ipl)(void) = (void *) (uint64_t) current->ipl_continue; > --->*current = save; > ipl(); /* should not return */ > } > > void jump_to_IPL_code(uint64_t address) > { > /* store the subsystem information _after_ the bootmap was loaded */ > write_subsystem_identification(); > > /* prevent unknown IPL types in the guest */ > if (iplb.pbt == S390_IPL_TYPE_QEMU_SCSI) { > iplb.pbt = S390_IPL_TYPE_CCW; > set_iplb(&iplb); > } > > /* > * The IPL PSW is at address 0. We also must not overwrite the > * content of non-BIOS memory after we loaded the guest, so we > * save the original content and restore it in jump_to_IPL_2. > */ > ResetInfo *current = 0; > > --->save = *current; > > > > does something like > > > diff --git a/pc-bios/s390-ccw/jump2ipl.c b/pc-bios/s390-ccw/jump2ipl.c > index da13c43cc0..8839226803 100644 > --- a/pc-bios/s390-ccw/jump2ipl.c > +++ b/pc-bios/s390-ccw/jump2ipl.c > @@ -18,6 +18,7 @@ > typedef struct ResetInfo { > uint64_t ipl_psw; > uint32_t ipl_continue; > + uint32_t pad; > } ResetInfo; > > static ResetInfo save; > > > also work? If yes, both variants are valid. Either packed or explicit padding. > I don't believe this will work. I think the problem is that we're overwriting too much memory when we cast address 0 as a ResetInfo and then overwrite it (*current = save). I think we need the struct to be sized at 12-bytes instead of 16. -- -- Jason J. Herne (jjherne@linux.ibm.com)