From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:11364 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1731030AbfILLAO (ORCPT ); Thu, 12 Sep 2019 07:00:14 -0400 Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x8CAwJFx175463 for ; Thu, 12 Sep 2019 07:00:12 -0400 Received: from e06smtp07.uk.ibm.com (e06smtp07.uk.ibm.com [195.75.94.103]) by mx0b-001b2d01.pphosted.com with ESMTP id 2uymh00j71-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 12 Sep 2019 07:00:11 -0400 Received: from localhost by e06smtp07.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 12 Sep 2019 12:00:08 +0100 Subject: Re: [PATCH] KVM: s390: Do not leak kernel stack data in the KVM_S390_INTERRUPT ioctl References: <20190912090050.20295-1-thuth@redhat.com> <6905df78-95f0-3d6d-aaae-910cd2d7a232@redhat.com> <253e67f6-0a41-13e8-4ca2-c651d5fcdb69@redhat.com> <982f703f-73f1-30c2-031f-a430de7dc6a9@redhat.com> From: Christian Borntraeger Date: Thu, 12 Sep 2019 13:00:03 +0200 MIME-Version: 1.0 In-Reply-To: <982f703f-73f1-30c2-031f-a430de7dc6a9@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: <91dfd032-7529-d9f4-8239-60fa1e06977e@de.ibm.com> Sender: linux-s390-owner@vger.kernel.org List-ID: To: David Hildenbrand , Thomas Huth , Janosch Frank , kvm@vger.kernel.org Cc: Cornelia Huck , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org On 12.09.19 12:58, David Hildenbrand wrote: > On 12.09.19 11:20, Thomas Huth wrote: >> On 12/09/2019 11.14, David Hildenbrand wrote: >>> On 12.09.19 11:00, Thomas Huth wrote: >>>> When the userspace program runs the KVM_S390_INTERRUPT ioctl to inject >>>> an interrupt, we convert them from the legacy struct kvm_s390_interrupt >>>> to the new struct kvm_s390_irq via the s390int_to_s390irq() function. >>>> However, this function does not take care of all types of interrupts >>>> that we can inject into the guest later (see do_inject_vcpu()). Since we >>>> do not clear out the s390irq values before calling s390int_to_s390irq(), >>>> there is a chance that we copy unwanted data from the kernel stack >>>> into the guest memory later if the interrupt data has not been properly >>>> initialized by s390int_to_s390irq(). >>>> >>>> Specifically, the problem exists with the KVM_S390_INT_PFAULT_INIT >>>> interrupt: s390int_to_s390irq() does not handle it, but the function >>>> __deliver_pfault_init() will later copy the uninitialized stack data >>>> from the ext.ext_params2 into the guest memory. >>>> >>>> Fix it by handling that interrupt type in s390int_to_s390irq(), too. >>>> And while we're at it, make sure that s390int_to_s390irq() now >>>> directly returns -EINVAL for unknown interrupt types, so that we >>>> do not run into this problem again in case we add more interrupt >>>> types to do_inject_vcpu() sometime in the future. >>>> >>>> Signed-off-by: Thomas Huth >>>> --- >>>> arch/s390/kvm/interrupt.c | 10 ++++++++++ >>>> 1 file changed, 10 insertions(+) >>>> >>>> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c >>>> index 3e7efdd9228a..165dea4c7f19 100644 >>>> --- a/arch/s390/kvm/interrupt.c >>>> +++ b/arch/s390/kvm/interrupt.c >>>> @@ -1960,6 +1960,16 @@ int s390int_to_s390irq(struct kvm_s390_interrupt *s390int, >>>> case KVM_S390_MCHK: >>>> irq->u.mchk.mcic = s390int->parm64; >>>> break; >>>> + case KVM_S390_INT_PFAULT_INIT: >>>> + irq->u.ext.ext_params = s390int->parm; >>>> + irq->u.ext.ext_params2 = s390int->parm64; >>>> + break; >>>> + case KVM_S390_RESTART: >>>> + case KVM_S390_INT_CLOCK_COMP: >>>> + case KVM_S390_INT_CPU_TIMER: >>>> + break; >>>> + default: >>>> + return -EINVAL; >>>> } >>>> return 0; >>>> } >>>> >>> >>> Wouldn't a safe fix be to initialize the struct to zero in the caller? >> >> That's of course possible, too. But that means that we always have to >> zero out the whole structure, so that's a little bit more of overhead >> (well, it likely doesn't matter for such a legacy ioctl). > > I would vote for doing this as well. Yes, lets also do the designated initializer, add more text to the patch description (or should we not?) add cc stable and I will pick a v2. > >> >> But the more important question: Do we then still care of fixing the >> PFAULT_INIT interrupt here? Since it requires a parameter, the "case >> KVM_S390_INT_PFAULT_INIT:" part would be required here anyway. >> > > That's indeed true. > > Reviewed-by: David Hildenbrand > >> Thomas >> > >