From: Tony Krowiak <akrowiak@linux.ibm.com>
To: Cornelia Huck <cohuck@redhat.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 08:59:59 -0400 [thread overview]
Message-ID: <315c8220-3dfa-1b19-266a-b9d9069bbe73@linux.ibm.com> (raw)
In-Reply-To: <20190627092518.1f8d7d48.cohuck@redhat.com>
On 6/27/19 3:25 AM, Cornelia Huck wrote:
> 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.
No problem, just wanted to make sure it didn't get lost in the shuffle.
>
>
>>
>> Tony K
>>
>>>
>>>>
>>>
>>
>
next prev parent reply other threads:[~2019-06-27 13:00 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
2019-06-27 12:59 ` Tony Krowiak [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=315c8220-3dfa-1b19-266a-b9d9069bbe73@linux.ibm.com \
--to=akrowiak@linux.ibm.com \
--cc=alex.williamson@redhat.com \
--cc=borntraeger@de.ibm.com \
--cc=cohuck@redhat.com \
--cc=david@redhat.com \
--cc=frankja@linux.ibm.com \
--cc=freude@linux.ibm.com \
--cc=heiko.carstens@de.ibm.com \
--cc=kvm@vger.kernel.org \
--cc=kwankhede@nvidia.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-s390@vger.kernel.org \
--cc=mjrosato@linux.ibm.com \
--cc=pasic@linux.ibm.com \
--cc=pmorel@linux.ibm.com \
--cc=schwidefsky@de.ibm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).