Messages in this thread | | | Subject | Re: [PATCH v6 00/10] s390: vfio-ap: dynamic configuration support | From | Tony Krowiak <> | Date | Tue, 15 Oct 2019 16:33:39 -0400 |
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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 <akrowiak@linux.ibm.com> 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(-) >>>
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