On Mon, Aug 23, 2021 at 07:14:18PM -0700, Andi Kleen wrote: > > On 8/23/2021 6:04 PM, Dan Williams wrote: > > On Mon, Aug 23, 2021 at 5:31 PM Kuppuswamy, Sathyanarayanan > > <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx> wrote: > > > > > > > > > On 8/23/21 4:56 PM, Michael S. Tsirkin wrote: > > > > > Add a new variant of pci_iomap for mapping all PCI resources > > > > > of a devices as shared memory with a hypervisor in a confidential > > > > > guest. > > > > > > > > > > Signed-off-by: Andi Kleen<ak@xxxxxxxxxxxxxxx> > > > > > Signed-off-by: Kuppuswamy Sathyanarayanan<sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx> > > > > I'm a bit puzzled by this part. So why should the guest*not* map > > > > pci memory as shared? And if the answer is never (as it seems to be) > > > > then why not just make regular pci_iomap DTRT? > > > It is in the context of confidential guest (where VMM is un-trusted). So > > > we don't want to make all PCI resource as shared. It should be allowed > > > only for hardened drivers/devices. > > That's confusing, isn't device authorization what keeps unaudited > > drivers from loading against untrusted devices? I'm feeling like > > Michael that this should be a detail that drivers need not care about > > explicitly, in which case it does not need to be exported because the > > detail can be buried in lower levels. > > We originally made it default (similar to AMD), but it during code audit we > found a lot of drivers who do ioremap early outside the probe function. > Since it would be difficult to change them all we made it opt-in, which > ensures that only drivers that have been enabled can talk with the host at > all and can't be attacked. That made the problem of hardening all these > drivers a lot more practical. > > Currently we only really need virtio and MSI-X shared, so for changing two > places in the tree you avoid a lot of headache elsewhere. > > Note there is still a command line option to override if you want to allow > and load other drivers. > > -Andi I see. Hmm. It's a bit of a random thing to do it at the map time though. E.g. DMA is all handled transparently behind the DMA API. Hardening is much more than just replacing map with map_shared and I suspect what you will end up with is basically vendors replacing map with map shared to make things work for their users and washing their hands. I would say an explicit flag in the driver that says "hardened" and refusing to init a non hardened one would be better. -- MST
