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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 8 Apr 2020 12:39:52 +0100 Received: from d06av26.portsmouth.uk.ibm.com (d06av26.portsmouth.uk.ibm.com [9.149.105.62]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 038BeA0834472178 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 8 Apr 2020 11:40:10 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 05877AE04D; Wed, 8 Apr 2020 11:40:10 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7A0E5AE045; Wed, 8 Apr 2020 11:40:09 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.145.153.96]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 8 Apr 2020 11:40:09 +0000 (GMT) Subject: Re: [PATCH 2/2] KVM: s390: Return last valid slot if approx index is out-of-bounds To: Paolo Bonzini , Claudio Imbrenda , Sean Christopherson Cc: Janosch Frank , David Hildenbrand , Cornelia Huck , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+d889b59b2bb87d4047a2@syzkaller.appspotmail.com References: <20200408064059.8957-1-sean.j.christopherson@intel.com> <20200408064059.8957-3-sean.j.christopherson@intel.com> <20200408122138.71493308@p-imbrenda> <40b325c7-ca24-3513-b2fa-1e9397c9e353@redhat.com> From: Christian Borntraeger Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <40b325c7-ca24-3513-b2fa-1e9397c9e353@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 20040811-0008-0000-0000-0000036CD0B1 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 20040811-0009-0000-0000-00004A8E6DD3 Message-Id: <875ba09c-eb1b-1cdd-f198-0bfbdb607d4b@de.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.676 definitions=2020-04-07_10:2020-04-07,2020-04-07 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 impostorscore=0 mlxscore=0 malwarescore=0 phishscore=0 priorityscore=1501 adultscore=0 lowpriorityscore=0 spamscore=0 bulkscore=0 clxscore=1015 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004080093 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08.04.20 13:33, Paolo Bonzini wrote: > On 08/04/20 12:21, Claudio Imbrenda wrote: >> on s390 memory always starts at 0; you can't even boot a system missing >> the first pages of physical memory, so this means this situation would >> never happen in practice. >> >> of course, a malicious userspace program could create an (unbootable) VM >> and trigger this bug, so the patch itself makes sense. >> >> Reviewed-by: Claudio Imbrenda > > What about using KVM just for isolation and not just to run a full-blown > OS (that is, you might even only have the guest run in problem state)? > Would that be feasible on s390? You always need 2 prefix pages. Otherwise the SIE instruction refuses to start. By default this starts as address 0. You might be also to set the prefix register to something else adn then this could maybe work.