KVM: x86/mmu: Prevent aliased memslot GFNs

Add a few sanity checks to prevent memslot GFNs from ever having alias bits
set.

Like other Coco technologies, TDX has the concept of private and shared
memory. For TDX the private and shared mappings are managed on separate
EPT roots. The private half is managed indirectly though calls into a
protected runtime environment called the TDX module, where the shared half
is managed within KVM in normal page tables.

For TDX, the shared half will be mapped in the higher alias, with a "shared
bit" set in the GPA. However, KVM will still manage it with the same
memslots as the private half. This means memslot looks ups and zapping
operations will be provided with a GFN without the shared bit set.

If these memslot GFNs ever had the bit that selects between the two aliases
it could lead to unexpected behavior in the complicated code that directs
faulting or zapping operations between the roots that map the two aliases.

As a safety measure, prevent memslots from being set at a GFN range that
contains the alias bit.

Also, check in the kvm_faultin_pfn() for the fault path. This later check
does less today, as the alias bits are specifically stripped from the GFN
being checked, however future code could possibly call in to the fault
handler in a way that skips this stripping. Since kvm_faultin_pfn() now
has many references to vcpu->kvm, extract it to local variable.

Link: https://lore.kernel.org/kvm/ZpbKqG_ZhCWxl-Fc@google.com/
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Message-ID: <20240718211230.1492011-19-rick.p.edgecombe@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

0 files changed, 0 insertions, 0 deletions