On Fri, 13 Sep 2019 17:26:48 -0400 Tony Krowiak <akrowiak@xxxxxxxxxxxxx> 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. 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. > > 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(-) >
