KVM: x86/mmu: Sanity check that __kvm_faultin_pfn() doesn't create noslot pfns

WARN if __kvm_faultin_pfn() generates a "no slot" pfn, and gracefully
handle the unexpected behavior instead of continuing on with dangerous
state, e.g. tdp_mmu_map_handle_target_level() _only_ checks fault->slot,
and so could install a bogus PFN into the guest.

The existing code is functionally ok, because kvm_faultin_pfn() pre-checks
all of the cases that result in KVM_PFN_NOSLOT, but it is unnecessarily
unsafe as it relies on __gfn_to_pfn_memslot() getting the _exact_ same
memslot, i.e. not a re-retrieved pointer with KVM_MEMSLOT_INVALID set.
And checking only fault->slot would fall apart if KVM ever added a flag or
condition that forced emulation, similar to how KVM handles writes to
read-only memslots.

Cc: David Matlack <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
Reviewed-by: Kai Huang <[email protected]>
Message-ID: <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

0 files changed, 0 insertions, 0 deletions