Messages in this thread | | | Subject | Re: [PATCH v5] virtio-blk: Add validation for block size in config space | From | Max Gurtovoy <> | Date | Tue, 24 Aug 2021 13:11:14 +0300 |
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On 8/24/2021 5:47 AM, Jason Wang wrote: > On Tue, Aug 24, 2021 at 6:31 AM Max Gurtovoy <mgurtovoy@nvidia.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.
> > That's why we need to validate any input from them. > > Thanks > >>> Yongji - I think the commit log should be much more explicit that >>> this is hardening. Otherwise people get confused and think this >>> needs a CVE or a backport for security. >>>
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