Messages in this thread | | | From | Paolo Bonzini <> | Subject | Re: [RFC] /dev/ioasid uAPI proposal | Date | Fri, 4 Jun 2021 18:10:51 +0200 |
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On 04/06/21 18:03, Jason Gunthorpe wrote: > On Fri, Jun 04, 2021 at 05:57:19PM +0200, Paolo Bonzini wrote: >> I don't want a security proof myself; I want to trust VFIO to make the right >> judgment and I'm happy to defer to it (via the KVM-VFIO device). >> >> Given how KVM is just a device driver inside Linux, VMs should be a slightly >> more roundabout way to do stuff that is accessible to bare metal; not a way >> to gain extra privilege. > > Okay, fine, lets turn the question on its head then. > > VFIO should provide a IOCTL VFIO_EXECUTE_WBINVD so that userspace VFIO > application can make use of no-snoop optimizations. The ability of KVM > to execute wbinvd should be tied to the ability of that IOCTL to run > in a normal process context. > > So, under what conditions do we want to allow VFIO to giave a process > elevated access to the CPU:
Ok, I would definitely not want to tie it *only* to CAP_SYS_RAWIO (i.e. #2+#3 would be worse than what we have today), but IIUC the proposal (was it yours or Kevin's?) was to keep #2 and add #1 with an enable/disable ioctl, which then would be on VFIO and not on KVM. I assumed Alex was more or less okay with it, given he included me in the discussion.
If later y'all switch to "it's always okay to issue the enable/disable ioctl", I guess the rationale would be documented in the commit message.
Paolo
>>> 1) User has access to a device that can issue no-snoop TLPS >>> 2) User has access to an IOMMU that can not block no-snoop (today) >>> 3) Require CAP_SYS_RAW_IO >>> 4) Anyone > > Jason >
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