On 10/06/2015 10:33 AM, Stephen Hemminger wrote: > Other than implementation objections, so far the two main arguments > against this reduce to: > 1. If you allow UIO ioctl then it opens an API hook for all the crap out > of tree UIO drivers to do what they want. > 2. If you allow UIO MSI-X then you are expanding the usage of userspace > device access in an insecure manner. > > Another alternative which I explored was making a version of VFIO that > works without IOMMU. It solves #1 but actually increases the likely negative > response to arguent #2. This would keep same API, and avoid having to > modify UIO. But we would still have the same (if not more resistance) > from IOMMU developers who believe all systems have to be secure against > root.
vfio's charter was explicitly aiming for modern setups with iommus. This could be revisited, but I agree it will have even more resistance, justified IMO. btw, (2) doesn't really add any insecurity. The user could already poke at the msix tables (as well as perform DMA); they just couldn't get a useful interrupt out of them. Maybe a module parameter "allow_insecure_dma" can be added to uio_pci_generic. Without the parameter, bus mastering and msix is disabled, with the parameter it is allowed. This requires the sysadmin to take a positive step in order to make use of their hardware.
