From: Cornelia Huck <cohuck@redhat.com>
To: Tony Krowiak <akrowiak@linux.ibm.com>
Cc: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org, freude@linux.ibm.com,
borntraeger@de.ibm.com, frankja@linux.ibm.com, david@redhat.com,
mjrosato@linux.ibm.com, schwidefsky@de.ibm.com,
heiko.carstens@de.ibm.com, pmorel@linux.ibm.com,
pasic@linux.ibm.com, alex.williamson@redhat.com,
kwankhede@nvidia.com
Subject: Re: [PATCH v4 3/7] s390: zcrypt: driver callback to indicate resource in use
Date: Thu, 27 Jun 2019 09:25:18 +0200 [thread overview]
Message-ID: <20190627092518.1f8d7d48.cohuck@redhat.com> (raw)
In-Reply-To: <44f13e89-2fb4-bf8c-7849-641aae8d08cc@linux.ibm.com>
On Wed, 26 Jun 2019 17:13:50 -0400
Tony Krowiak <akrowiak@linux.ibm.com> wrote:
> On 6/19/19 9:04 AM, Tony Krowiak wrote:
> > On 6/18/19 12:25 PM, Cornelia Huck wrote:
> >> On Thu, 13 Jun 2019 15:39:36 -0400
> >> Tony Krowiak <akrowiak@linux.ibm.com> wrote:
> >>
> >>> Introduces a new driver callback to prevent a root user from unbinding
> >>> an AP queue from its device driver if the queue is in use. This prevents
> >>> a root user from inadvertently taking a queue away from a guest and
> >>> giving it to the host, or vice versa. The callback will be invoked
> >>> whenever a change to the AP bus's apmask or aqmask sysfs interfaces may
> >>> result in one or more AP queues being removed from its driver. If the
> >>> callback responds in the affirmative for any driver queried, the change
> >>> to the apmask or aqmask will be rejected with a device in use error.
> >>>
> >>> For this patch, only non-default drivers will be queried. Currently,
> >>> there is only one non-default driver, the vfio_ap device driver. The
> >>> vfio_ap device driver manages AP queues passed through to one or more
> >>> guests and we don't want to unexpectedly take AP resources away from
> >>> guests which are most likely independently administered.
> >>>
> >>> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> >>> ---
> >>> drivers/s390/crypto/ap_bus.c | 138
> >>> +++++++++++++++++++++++++++++++++++++++++--
> >>> drivers/s390/crypto/ap_bus.h | 3 +
> >>> 2 files changed, 135 insertions(+), 6 deletions(-)
> >>
> >> Hm... I recall objecting to this patch before, fearing that it makes it
> >> possible for a bad actor to hog resources that can't be removed by
> >> root, even forcefully. (I have not had time to look at the intervening
> >> versions, so I might be missing something.)
> >>
> >> Is there a way for root to forcefully override this?
> >
> > You recall correctly; however, after many internal crypto team
> > discussions, it was decided that this feature was important
> > and should be kept.
> >
> > Allow me to first address your fear that a bad actor can hog
> > resources that can't be removed by root. With this enhancement,
> > there is nothing preventing a root user from taking resources
> > from a matrix mdev, it simply forces him/her to follow the
> > proper procedure. The resources to be removed must first be
> > unassigned from the matrix mdev to which they are assigned.
> > The AP bus's /sys/bus/ap/apmask and /sys/bus/ap/aqmask
> > sysfs attributes can then be edited to transfer ownership
> > of the resources to zcrypt.
> >
> > The rationale for keeping this feature is:
> >
> > * It is a bad idea to steal an adapter in use from a guest. In the worst
> > case, the guest could end up without access to any crypto adapters
> > without knowing why. This could lead to performance issues on guests
> > that rely heavily on crypto such as guests used for blockchain
> > transactions.
> >
> > * There are plenty of examples in linux of the kernel preventing a root
> > user from performing a task. For example, a module can't be removed
> > if references are still held for it. Another example would be trying
> > to bind a CEX4 adapter to a device driver not registered for CEX4;
> > this action will also be rejected.
> >
> > * The semantics are much cleaner and the logic is far less complicated.
> >
> > * It forces the use of the proper procedure to change ownership of AP
> > queues.
> >
>
> Any feedback on this?
Had not yet time to look at this, sorry.
>
> Tony K
>
> >
> >>
> >
>
next prev parent reply other threads:[~2019-06-27 7:25 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-13 19:39 [PATCH v4 0/7] s390: vfio-ap: dynamic configuration support Tony Krowiak
2019-06-13 19:39 ` [PATCH v4 1/7] s390: vfio-ap: Refactor vfio_ap driver probe and remove callbacks Tony Krowiak
2019-06-17 8:27 ` Harald Freudenberger
2019-06-17 14:24 ` Tony Krowiak
2019-06-18 16:14 ` Cornelia Huck
2019-06-19 12:31 ` Tony Krowiak
2019-06-13 19:39 ` [PATCH v4 2/7] s390: vfio-ap: wait for queue empty on queue reset Tony Krowiak
2019-06-17 8:47 ` Harald Freudenberger
2019-06-17 14:29 ` Tony Krowiak
2019-06-13 19:39 ` [PATCH v4 3/7] s390: zcrypt: driver callback to indicate resource in use Tony Krowiak
2019-06-17 9:28 ` Harald Freudenberger
2019-06-17 14:37 ` Tony Krowiak
2019-06-18 16:25 ` Cornelia Huck
2019-06-19 13:04 ` Tony Krowiak
2019-06-26 21:13 ` Tony Krowiak
2019-06-27 7:25 ` Cornelia Huck [this message]
2019-06-27 12:59 ` Tony Krowiak
2019-07-01 19:26 ` Cornelia Huck
2019-07-08 14:27 ` Tony Krowiak
2019-07-09 10:49 ` Cornelia Huck
2019-07-09 21:11 ` Tony Krowiak
2019-06-13 19:39 ` [PATCH v4 4/7] s390: vfio-ap: implement in-use callback for vfio_ap driver Tony Krowiak
2019-06-13 19:39 ` [PATCH v4 5/7] s390: vfio-ap: allow assignment of unavailable AP resources to mdev device Tony Krowiak
2019-06-17 10:05 ` Harald Freudenberger
2019-06-17 15:07 ` Tony Krowiak
2019-06-18 6:49 ` Harald Freudenberger
2019-06-19 13:39 ` Tony Krowiak
2019-06-13 19:39 ` [PATCH v4 6/7] s390: vfio-ap: allow hot plug/unplug of AP resources using " Tony Krowiak
2019-06-13 19:39 ` [PATCH v4 7/7] s390: vfio-ap: update documentation Tony Krowiak
2019-06-17 11:42 ` Harald Freudenberger
2019-06-17 15:21 ` Tony Krowiak
2019-07-09 15:30 ` [PATCH v4 0/7] s390: vfio-ap: dynamic configuration support Halil Pasic
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