From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:41602 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2387777AbfJOUdt (ORCPT ); Tue, 15 Oct 2019 16:33:49 -0400 Subject: Re: [PATCH v6 00/10] s390: vfio-ap: dynamic configuration support References: <1568410018-10833-1-git-send-email-akrowiak@linux.ibm.com> <20191008124807.49022238.pasic@linux.ibm.com> From: Tony Krowiak Message-ID: <99390e19-58f6-0f7e-0632-451d138671bc@linux.ibm.com> Date: Tue, 15 Oct 2019 16:33:39 -0400 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format="flowed" Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-s390-owner@vger.kernel.org List-ID: To: Pierre Morel , Halil Pasic Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, freude@linux.ibm.com, borntraeger@de.ibm.com, cohuck@redhat.com, mjrosato@linux.ibm.com, alex.williamson@redhat.com, kwankhede@nvidia.com, jjherne@linux.ibm.com On 10/8/19 8:57 AM, Pierre Morel wrote: > > On 10/8/19 12:48 PM, Halil Pasic wrote: >> On Fri, 13 Sep 2019 17:26:48 -0400 >> Tony Krowiak wrote: >> >>> The current design for AP pass-through does not support making dynamic >>> changes to the AP matrix of a running guest resulting in three >>> deficiencies >>> this patch series is intended to mitigate: >>> >>> 1. Adapters, domains and control domains can not be added to or removed >>>     from a running guest. In order to modify a guest's AP configuration, >>>     the guest must be terminated; only then can AP resources be assigned >>>     to or unassigned from the guest's matrix mdev. The new AP >>> configuration >>>     becomes available to the guest when it is subsequently restarted. >>> >>> 2. The AP bus's /sys/bus/ap/apmask and /sys/bus/ap/aqmask interfaces can >>>     be modified by a root user without any restrictions. A change to >>> either >>>     mask can result in AP queue devices being unbound from the vfio_ap >>>     device driver and bound to a zcrypt device driver even if a guest is >>>     using the queues, thus giving the host access to the guest's private >>>     crypto data and vice versa. >>> >>> 3. The APQNs derived from the Cartesian product of the APIDs of the >>>     adapters and APQIs of the domains assigned to a matrix mdev must >>>     reference an AP queue device bound to the vfio_ap device driver. >>> >>> This patch series introduces the following changes to the current design >>> to alleviate the shortcomings described above as well as to implement >>> more >>> of the AP architecture: >>> >>> 1. A root user will be prevented from making changes to the AP bus's >>>     /sys/bus/ap/apmask or /sys/bus/ap/aqmask if the ownership of an APQN >>>     changes from the vfio_ap device driver to a zcrypt driver when >>> the APQN >>>     is assigned to a matrix mdev. >>> >>> 2. The sysfs bind/unbind interfaces will be disabled for the vfio_ap >>>     device driver. >>> >> Doesn't this have the potential of breaking some userspace stuff that >> might be out there? >> >>> 3. Allow AP resources to be assigned to or removed from a matrix mdev >>>     while a guest is using it and hot plug the resource into or hot >>> unplug >>>     the resource from the running guest. >> This looks like a natural extension of the interface -- i.e. should not >> break any userspace. >> >>> 4. Allow assignment of an AP adapter or domain to a matrix mdev even >>> if it >>>     results in assignment of an APQN that does not reference an AP queue >>>     device bound to the vfio_ap device driver, as long as the APQN is >>> owned >>>     by the vfio_ap driver. Allowing over-provisioning of AP resources >>>     better models the architecture which does not preclude assigning AP >>>     resources that are not yet available in the system. If/when the >>> queue >>>     becomes available to the host, it will immediately also become >>> available >>>     to the guest. >> Same here -- I don't think this change breaks any userspace. >> >>> 1. Rationale for changes to AP bus's apmask/aqmask interfaces: >>> ---------------------------------------------------------- >>> Due to the extremely sensitive nature of cryptographic data, it is >>> imperative that great care be taken to ensure that such data is secured. >>> Allowing a root user, either inadvertently or maliciously, to configure >>> these masks such that a queue is shared between the host and a guest is >>> not only avoidable, it is advisable. > > Just curious: how is it possible to do such a configuration? In the current implementation of dedicated crypto, there is nothing stopping a sysadmin from changing the apmask/aqmask in manner that transfers ownership of one more APQNs from the vfio_ap device driver to zcrypt which results in unbinding the queue devices from vfio_ap and binding them to the zcrypt drive. If a guest happens to be using the queue at the time, both the host and guest will have access. That is fixed by this series. > > >>>   It was suggested that this scenario >>> is better handled in user space with management software, but that does >>> not preclude a malicious administrator from using the sysfs interfaces >>> to gain access to a guest's crypto data. It was also suggested that this >>> scenario could be avoided by taking access to the adapter away from the >>> guest and zeroing out the queues prior to the vfio_ap driver >>> releasing the >>> device; however, stealing an adapter in use from a guest as a by-product >>> of an operation is bad and will likely cause problems for the guest >>> unnecessarily. It was decided that the most effective solution with the >>> least number of negative side effects is to prevent the situation at the >>> source. > > > Stealing an adapter in use by a guest, insn't it what is done if we > allow to unassign an AP/Domain using the unassign sysfs interface when > the mediated device is in use by the guest? Yes, but that is a deliberate action as opposed to a side effect of bind/unbind. It is the very definition of dynamic configuration (a.k.a., hot plug/unplug). > > >>> >>> 2. Rationale for disabling bind/unbind interfaces for vfio_ap driver: >>> ----------------------------------------------------------------- >>> By disabling the bind/unbind interfaces for the vfio_ap device driver, >>> the user is forced to use the AP bus's apmask/aqmask interfaces to >>> control >>> the probing and removing of AP queues. There are two primary reasons for >>> disabling the bind/unbind interfaces for the vfio_ap device driver: >>> >>> * The device architecture does not provide a means to prevent unbinding >>>    a device from a device driver, so an AP queue device can be unbound >>>    from the vfio_ap driver even when the queue is in use by a guest. By >>>    disabling the unbind interface, the user is forced to use the AP >>> bus's >>>    apmask/aqmask interfaces which will prevent this. >>> >> Isn't this fixed by your filtering (if implemented correctly)? BTW I >> believe >> it solves the problem regardless whether the unbind was triggered by the >> drivers unbind attribute or by a[pq]mask >> >>> * Binding of AP queues is controlled by the AP bus /sys/bus/ap/apmask >>> and >>>    /sys/bus/ap/aqmask interfaces. If the masks indicate that an APQN is >>>    owned by zcrypt, trying to bind it to the vfio_ap device driver will >>>    fail; therefore, the bind interface is somewhat redundant and >>> certainly >>>    unnecessary. >>> >>> >>> Tony Krowiak (10): >>>    s390: vfio-ap: Refactor vfio_ap driver probe and remove callbacks >>>    s390: vfio-ap: allow assignment of unavailable AP resources to mdev >>>      device >>>    s390: vfio-ap: allow hot plug/unplug of AP resources using mdev >>> device >>>    s390: vfio-ap: filter CRYCB bits for unavailable queue devices >>>    s390: vfio-ap: sysfs attribute to display the guest CRYCB >>>    s390: vfio-ap: update guest CRYCB in vfio_ap probe and remove >>>      callbacks >>>    s390: zcrypt: driver callback to indicate resource in use >>>    s390: vfio-ap: implement in-use callback for vfio_ap driver >>>    s390: vfio-ap: added versioning to vfio_ap module >>>    s390: vfio-ap: update documentation >> I believe it would be worthwhile to reorder the patches (fixes and >> re-factoring first, the features). >> >> Regards, >> Halil >> >>>   Documentation/s390/vfio-ap.rst        | 899 >>> +++++++++++++++++++++++++--------- >>>   drivers/s390/crypto/ap_bus.c          | 144 +++++- >>>   drivers/s390/crypto/ap_bus.h          |   4 + >>>   drivers/s390/crypto/vfio_ap_drv.c     |  27 +- >>>   drivers/s390/crypto/vfio_ap_ops.c     | 610 ++++++++++++++--------- >>>   drivers/s390/crypto/vfio_ap_private.h |  12 +- >>>   6 files changed, 1200 insertions(+), 496 deletions(-) >>>