On Tue, Aug 24, 2021 at 6:11 PM Max Gurtovoy <mgurtovoy@xxxxxxxxxx> wrote: > > > On 8/24/2021 5:47 AM, Jason Wang wrote: > > On Tue, Aug 24, 2021 at 6:31 AM Max Gurtovoy <mgurtovoy@xxxxxxxxxx> 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. Thanks, Yongji
