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Date: Tue, 24 Aug 2021 16:48:18 +0300 From: Max Gurtovoy <mgurtovoy@...dia.com> To: Yongji Xie <xieyongji@...edance.com> CC: Jason Wang <jasowang@...hat.com>, "Michael S. Tsirkin" <mst@...hat.com>, Stefan Hajnoczi <stefanha@...hat.com>, virtualization <virtualization@...ts.linux-foundation.org>, <linux-block@...r.kernel.org>, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v5] virtio-blk: Add validation for block size in config space On 8/24/2021 4:38 PM, Yongji Xie wrote: > On Tue, Aug 24, 2021 at 9:30 PM Max Gurtovoy <mgurtovoy@...dia.com> wrote: >> >> On 8/24/2021 3:52 PM, Yongji Xie wrote: >>> On Tue, Aug 24, 2021 at 6:11 PM Max Gurtovoy <mgurtovoy@...dia.com> wrote: >>>> On 8/24/2021 5:47 AM, Jason Wang wrote: >>>>> On Tue, Aug 24, 2021 at 6:31 AM Max Gurtovoy <mgurtovoy@...dia.com> wrote: >>>>>> On 8/23/2021 3:13 PM, Michael S. Tsirkin wrote: >>>>>>> On Mon, Aug 23, 2021 at 01:45:31PM +0300, Max Gurtovoy wrote: >>>>>>>> It helpful if there is a justification for this. >>>>>>>> >>>>>>>> In this case, no such HW device exist and the only device that can cause >>>>>>>> this trouble today is user space VDUSE device that must be validated by the >>>>>>>> emulation VDUSE kernel driver. >>>>>>>> >>>>>>>> Otherwise, will can create 1000 commit like this in the virtio level (for >>>>>>>> example for each feature for each virtio device). >>>>>>> Yea, it's a lot of work but I don't think it's avoidable. >>>>>>> >>>>>>>>>>>>> And regardless of userspace device, we still need to fix it for other cases. >>>>>>>>>>>> which cases ? Do you know that there is a buggy HW we need to workaround ? >>>>>>>>>>>> >>>>>>>>>>> No, there isn't now. But this could be a potential attack surface if >>>>>>>>>>> the host doesn't trust the device. >>>>>>>>>> If the host doesn't trust a device, why it continues using it ? >>>>>>>>>> >>>>>>>>> IIUC this is the case for the encrypted VMs. >>>>>>>> what do you mean encrypted VM ? >>>>>>>> >>>>>>>> And how this small patch causes a VM to be 100% encryption supported ? >>>>>>>> >>>>>>>>>> Do you suggest we do these workarounds in all device drivers in the kernel ? >>>>>>>>>> >>>>>>>>> Isn't it the driver's job to validate some unreasonable configuration? >>>>>>>> The check should be in different layer. >>>>>>>> >>>>>>>> Virtio blk driver should not cover on some strange VDUSE stuff. >>>>>>> Yes I'm not convinced VDUSE is a valid use-case. I think that for >>>>>>> security and robustness it should validate data it gets from userspace >>>>>>> right there after reading it. >>>>>>> But I think this is useful for the virtio hardening thing. >>>>>>> https://lwn.net/Articles/865216/ >>>>>> I don't see how this change is assisting confidential computing. >>>>>> >>>>>> Confidential computingtalks about encrypting guest memory from the host, >>>>>> and not adding some quirks to devices. >>>>> In the case of confidential computing, the hypervisor and hard device >>>>> is not in the trust zone. It means the guest doesn't trust the cloud >>>>> vendor. >>>> Confidential computing protects data during processing ("in-use" data). >>>> >>>> Nothing to do with virtio feature negotiation. >>>> >>> But if a misbehaving device can corrupt the guest memory, I think it >>> should be avoided. >> So don't say it's related to confidential computing, and fix it in the >> VDUSE kernel driver in the hypervisor. >> > What I mean is in confidential computing cases. An untrusted device > might corrupt the protected guest memory, it should be avoided. This patch has nothing to do with confidential computing by definition (virtio feature negotiation are not "in-use" data). It's device configuration space. MST, I prefer adding quirks for vDPA devices in VDUSE driver and not adding workarounds to virtio driver. I guess this patch can stay but future patches like this shouldn't be merged without a very good reason. > > Thanks, > Yongji
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