On Sat, Oct 9, 2021 at 2:53 AM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote: > > On Fri, Oct 08, 2021 at 05:37:07PM -0700, Kuppuswamy Sathyanarayanan wrote: > > From: Andi Kleen <ak@xxxxxxxxxxxxxxx> > > > > For Confidential VM guests like TDX, the host is untrusted and hence > > the devices emulated by the host or any data coming from the host > > cannot be trusted. So the drivers that interact with the outside world > > have to be hardened by sharing memory with host on need basis > > with proper hardening fixes. > > > > For the PCI driver case, to share the memory with the host add > > pci_iomap_host_shared() and pci_iomap_host_shared_range() APIs. > > > > Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx> > > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx> > > So I proposed to make all pci mappings shared, eliminating the need > to patch drivers. > > To which Andi replied > One problem with removing the ioremap opt-in is that > it's still possible for drivers to get at devices without going through probe. > > To which Greg replied: > https://lore.kernel.org/all/YVXBNJ431YIWwZdQ@xxxxxxxxx/ > If there are in-kernel PCI drivers that do not do this, they need to be > fixed today. > > Can you guys resolve the differences here? I agree with you and Greg here. If a driver is accessing hardware resources outside of the bind lifetime of one of the devices it supports, and in a way that neither modrobe-policy nor device-authorization -policy infrastructure can block, that sounds like a bug report. Fix those drivers instead of sprinkling ioremap_shared in select places and with unclear rules about when a driver is allowed to do "shared" mappings. Let the new device-authorization mechanism (with policy in userspace) be the central place where all of these driver "trust" issues are managed. > And once they are resolved, mention this in the commit log so > I don't get to re-read the series just to find out nothing > changed in this respect? > > I frankly do not believe we are anywhere near being able to harden > an arbitrary kernel config against attack. > How about creating a defconfig that makes sense for TDX then? > Anyone deviating from that better know what they are doing, > this API tweaking is just putting policy into the kernel ... Right, userspace authorization policy and select driver fixups seems to be the answer to the raised concerns.
