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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Mon, 9 Sep 2019 17:21:50 +0100 Received: from d06av23.portsmouth.uk.ibm.com (d06av23.portsmouth.uk.ibm.com [9.149.105.59]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x89GLmqV60883142 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 9 Sep 2019 16:21:48 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6BD31A4055; Mon, 9 Sep 2019 16:21:48 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 10263A404D; Mon, 9 Sep 2019 16:21:48 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.145.65.169]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 9 Sep 2019 16:21:47 +0000 (GMT) Subject: Re: [PATCH] kvm_s390_vm_start_migration: check dirty_bitmap before using it as target for memset() To: Igor Mammedov , linux-kernel@vger.kernel.org Cc: david@redhat.com, cohuck@redhat.com, Janosch Frank , Claudio Imbrenda References: <20190909145545.11759-1-imammedo@redhat.com> From: Christian Borntraeger Openpgp: preference=signencrypt Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190909145545.11759-1-imammedo@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 19090916-0028-0000-0000-00000399D984 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19090916-0029-0000-0000-0000245C3998 Message-Id: <4668e4e9-c0bc-3647-6387-20c6f8107ed3@de.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-09-09_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=927 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1909090166 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Adding Janosch (co-maintainer) and Claudio (author of that code) On 09.09.19 16:55, Igor Mammedov wrote: > If userspace doesn't set KVM_MEM_LOG_DIRTY_PAGES on memslot before calling > kvm_s390_vm_start_migration(), kernel will oops with: > > Unable to handle kernel pointer dereference in virtual kernel address space > Failing address: 0000000000000000 TEID: 0000000000000483 > Fault in home space mode while using kernel ASCE. > AS:0000000002a2000b R2:00000001bff8c00b R3:00000001bff88007 S:00000001bff91000 P:000000000000003d > Oops: 0004 ilc:2 [#1] SMP > ... > Call Trace: > ([<001fffff804ec552>] kvm_s390_vm_set_attr+0x347a/0x3828 [kvm]) > [<001fffff804ecfc0>] kvm_arch_vm_ioctl+0x6c0/0x1998 [kvm] > [<001fffff804b67e4>] kvm_vm_ioctl+0x51c/0x11a8 [kvm] > [<00000000008ba572>] do_vfs_ioctl+0x1d2/0xe58 > [<00000000008bb284>] ksys_ioctl+0x8c/0xb8 > [<00000000008bb2e2>] sys_ioctl+0x32/0x40 > [<000000000175552c>] system_call+0x2b8/0x2d8 > INFO: lockdep is turned off. > Last Breaking-Event-Address: > [<0000000000dbaf60>] __memset+0xc/0xa0 > > due to ms->dirty_bitmap being NULL, which migh crash the host. > > Make sure that ms->dirty_bitmap is set before using it or > print a warning and return -ENIVAL otherwise. > > Signed-off-by: Igor Mammedov > --- > > PS: > keeping it private for now as issue might DoS host, > I'll leave it upto maintainers to decide if it should be handled as security > bug (I'm not sure what process for handling such bugs should be used). I think its fine to send to the public lists. Its just a bug and with cc stable this should cascade quickly to the right places. > > > arch/s390/kvm/kvm-s390.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c > index f329dcb3f44c..dfba51c9d60c 100644 > --- a/arch/s390/kvm/kvm-s390.c > +++ b/arch/s390/kvm/kvm-s390.c > @@ -1018,6 +1018,10 @@ static int kvm_s390_vm_start_migration(struct kvm *kvm) > /* mark all the pages in active slots as dirty */ > for (slotnr = 0; slotnr < slots->used_slots; slotnr++) { > ms = slots->memslots + slotnr; > + if (!ms->dirty_bitmap) { > + WARN(1, "ms->dirty_bitmap == NULL\n"); I would prefer to not have a WARN_ON. Otherwise this would allow a malicious user to spam the log. > + return -EINVAL; > + } > /* > * The second half of the bitmap is only used on x86, > * and would be wasted otherwise, so we put it to good >