KVM/arm64 currently considers that any memory access outside of a
memslot is a MMIO access. This so far has served us very well, but
obviously relies on the guest trusting the host, and especially
userspace to do the right thing.
As we keep on hacking away at pKVM, it becomes obvious that this trust
model is not really fit for a confidential computing environment, and
that the guest would require some guarantees that emulation only
occurs on portions of the address space that have clearly been
identified for this purpose.
This series aims at providing the two sides of the above coin:
- a set of PV services (collectively called 'MMIO guard' -- better
name required!) where the guest can flag portion of its address
space that it considers as MMIO, with map/unmap semantics. Any
attempt to access a MMIO range outside of these regions will result
in an external abort being injected.
- a set of hooks into the ioremap code allowing a Linux guest to tell
KVM about things it want to consider as MMIO. I definitely hate this
part of the series, as it feels clumsy and brittle.
For now, the enrolment in this scheme is controlled by a guest kernel
command-line parameters, but it is expected that KVM will enforce this
for protected VMs.
Note that this crucially misses a save/restore interface for non
protected VMs, and I currently don't have a good solution for
that. Ideas welcome.
I also plan to use this series as a base for some other purposes,
namely to trick the guest in telling us how it maps things like
prefetchable BARs (see the discussion at [1]). That part is not
implemented yet, but there is already some provision to pass the MAIR
index across.
Patches on top of 5.14-rc1, branch pushed at the usual location.
[1] 20210429162906.32742-1-sdonthineni@xxxxxxxxxx
Marc Zyngier (16):
KVM: arm64: Generalise VM features into a set of flags
KVM: arm64: Don't issue CMOs when the physical address is invalid
KVM: arm64: Turn kvm_pgtable_stage2_set_owner into
kvm_pgtable_stage2_annotate
KVM: arm64: Add MMIO checking infrastructure
KVM: arm64: Plumb MMIO checking into the fault handling
KVM: arm64: Force a full unmap on vpcu reinit
KVM: arm64: Wire MMIO guard hypercalls
KVM: arm64: Add tracepoint for failed MMIO guard check
KVM: arm64: Advertise a capability for MMIO guard
KVM: arm64: Add some documentation for the MMIO guard feature
firmware/smccc: Call arch-specific hook on discovering KVM services
mm/ioremap: Add arch-specific callbacks on ioremap/iounmap calls
arm64: Implement ioremap/iounmap hooks calling into KVM's MMIO guard
arm64: Enroll into KVM's MMIO guard if required
arm64: Add a helper to retrieve the PTE of a fixmap
arm64: Register earlycon fixmap with the MMIO guard
.../admin-guide/kernel-parameters.txt | 3 +
Documentation/virt/kvm/arm/index.rst | 1 +
Documentation/virt/kvm/arm/mmio-guard.rst | 73 +++++++++++
arch/arm/include/asm/hypervisor.h | 1 +
arch/arm64/include/asm/fixmap.h | 2 +
arch/arm64/include/asm/hypervisor.h | 2 +
arch/arm64/include/asm/kvm_host.h | 14 ++-
arch/arm64/include/asm/kvm_mmu.h | 5 +
arch/arm64/include/asm/kvm_pgtable.h | 12 +-
arch/arm64/kernel/setup.c | 6 +
arch/arm64/kvm/arm.c | 14 ++-
arch/arm64/kvm/hyp/nvhe/mem_protect.c | 14 ++-
arch/arm64/kvm/hyp/pgtable.c | 36 +++---
arch/arm64/kvm/hypercalls.c | 20 +++
arch/arm64/kvm/mmio.c | 13 +-
arch/arm64/kvm/mmu.c | 117 ++++++++++++++++++
arch/arm64/kvm/trace_arm.h | 17 +++
arch/arm64/mm/ioremap.c | 107 ++++++++++++++++
arch/arm64/mm/mmu.c | 15 +++
drivers/firmware/smccc/kvm_guest.c | 4 +
include/linux/arm-smccc.h | 28 +++++
include/linux/io.h | 3 +
include/uapi/linux/kvm.h | 1 +
mm/ioremap.c | 13 +-
mm/vmalloc.c | 8 ++
25 files changed, 492 insertions(+), 37 deletions(-)
create mode 100644 Documentation/virt/kvm/arm/mmio-guard.rst
--
2.30.2
