Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v2 0/7] vfio/pci: SR-IOV support
To:     Alex Williamson <alex.williamson@redhat.com>
Cc:     "Tian, Kevin" <kevin.tian@intel.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "dev@dpdk.org" <dev@dpdk.org>,
        "mtosatti@redhat.com" <mtosatti@redhat.com>,
        "thomas@monjalon.net" <thomas@monjalon.net>,
        "bluca@debian.org" <bluca@debian.org>,
        "jerinjacobk@gmail.com" <jerinjacobk@gmail.com>,
        "Richardson, Bruce" <bruce.richardson@intel.com>,
        "cohuck@redhat.com" <cohuck@redhat.com>
References: <158213716959.17090.8399427017403507114.stgit@gimli.home>
 <AADFC41AFE54684AB9EE6CBC0274A5D19D79A8A7@SHSMSX104.ccr.corp.intel.com>
 <a6c04bac-0a37-f4c0-876e-e5cf2a8a6c3f@redhat.com>
 <20200305101406.02703e2a@w520.home>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <3e8db1d0-8afc-f1e9-e857-aead4717fa11@redhat.com>
Date:   Fri, 6 Mar 2020 11:35:21 +0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.9.0
MIME-Version: 1.0
In-Reply-To: <20200305101406.02703e2a@w520.home>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On 2020/3/6 =E4=B8=8A=E5=8D=881:14, Alex Williamson wrote:
> On Tue, 25 Feb 2020 14:09:07 +0800
> Jason Wang <jasowang@redhat.com> wrote:
>
>> On 2020/2/25 =E4=B8=8A=E5=8D=8810:33, Tian, Kevin wrote:
>>>> From: Alex Williamson
>>>> Sent: Thursday, February 20, 2020 2:54 AM
>>>>
>>>> Changes since v1 are primarily to patch 3/7 where the commit log is
>>>> rewritten, along with option parsing and failure logging based on
>>>> upstream discussions.  The primary user visible difference is that
>>>> option parsing is now much more strict.  If a vf_token option is
>>>> provided that cannot be used, we generate an error.  As a result of
>>>> this, opening a PF with a vf_token option will serve as a mechanism =
of
>>>> setting the vf_token.  This seems like a more user friendly API than
>>>> the alternative of sometimes requiring the option (VFs in use) and
>>>> sometimes rejecting it, and upholds our desire that the option is
>>>> always either used or rejected.
>>>>
>>>> This also means that the VFIO_DEVICE_FEATURE ioctl is not the only
>>>> means of setting the VF token, which might call into question whethe=
r
>>>> we absolutely need this new ioctl.  Currently I'm keeping it because=
 I
>>>> can imagine use cases, for example if a hypervisor were to support
>>>> SR-IOV, the PF device might be opened without consideration for a VF
>>>> token and we'd require the hypservisor to close and re-open the PF i=
n
>>>> order to set a known VF token, which is impractical.
>>>>
>>>> Series overview (same as provided with v1):
>>> Thanks for doing this!
>>>  =20
>>>> The synopsis of this series is that we have an ongoing desire to dri=
ve
>>>> PCIe SR-IOV PFs from userspace with VFIO.  There's an immediate need
>>>> for this with DPDK drivers and potentially interesting future use
>>> Can you provide a link to the DPDK discussion?
>>>  =20
>>>> cases in virtualization.  We've been reluctant to add this support
>>>> previously due to the dependency and trust relationship between the
>>>> VF device and PF driver.  Minimally the PF driver can induce a denia=
l
>>>> of service to the VF, but depending on the specific implementation,
>>>> the PF driver might also be responsible for moving data between VFs
>>>> or have direct access to the state of the VF, including data or stat=
e
>>>> otherwise private to the VF or VF driver.
>>> Just a loud thinking. While the motivation of VF token sounds reasona=
ble
>>> to me, I'm curious why the same concern is not raised in other usages=
.
>>> For example, there is no such design in virtio framework, where the
>>> virtio device could also be restarted, putting in separate process (v=
host-user),
>>> and even in separate VM (virtio-vhost-user), etc.
>>
>> AFAIK, the restart could only be triggered by either VM or qemu. But
>> yes, the datapath could be offloaded.
>>
>> But I'm not sure introducing another dedicated mechanism is better tha=
n
>> using the exist generic POSIX mechanism to make sure the connection
>> (AF_UINX) is secure.
>>
>>
>>>    Of course the para-
>>> virtualized attribute of virtio implies some degree of trust, but as =
you
>>> mentioned many SR-IOV implementations support VF->PF communication
>>> which also implies some level of trust. It's perfectly fine if VFIO j=
ust tries
>>> to do better than other sub-systems, but knowing how other people
>>> tackle the similar problem may make the whole picture clearer. =F0=9F=
=98=8A
>>>
>>> +Jason.
>>
>> I'm not quite sure e.g allowing userspace PF driver with kernel VF
>> driver would not break the assumption of kernel security model. At lea=
st
>> we should forbid a unprivileged PF driver running in userspace.
> It might be useful to have your opinion on this series, because that's
> exactly what we're trying to do here.  Various environments, DPDK
> specifically, want a userspace PF driver.  This series takes steps to
> mitigate the risk of having such a driver, such as requiring this VF
> token interface to extend the VFIO interface and validate participation
> around a PF that is not considered trusted by the kernel.


I may miss something. But what happens if:

- PF driver is running by unprivileged user
- PF is programmed to send translated DMA request
- Then unprivileged user can mangle the kernel data


> We also set
> a driver_override to try to make sure no host kernel driver can
> automatically bind to a VF of a user owned PF, only vfio-pci, but we
> don't prevent the admin from creating configurations where the VFs are
> used by other host kernel drivers.
>
> I think the question Kevin is inquiring about is whether virtio devices
> are susceptible to the type of collaborative, shared key environment
> we're creating here.  For example, can a VM or qemu have access to
> reset a virtio device in a way that could affect other devices, ex. FLR
> on a PF that could interfere with VF operation.  Thanks,


Right, but I'm not sure it can be done only via virtio or need support=20
from transport (e.g PCI).

Thanks


>
> Alex
>