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KVM: x86/mmu: Disallow guest from using !visible slots for page tables

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Explicitly inject a page fault if guest attempts to use a !visible gfn
as a page table.  kvm_vcpu_gfn_to_hva_prot() will naturally handle the
case where there is no memslot, but doesn't catch the scenario where the
gfn points at a KVM-internal memslot.

Letting the guest backdoor its way into accessing KVM-internal memslots
isn't dangerous on its own, e.g. at worst the guest can crash itself, but
disallowing the behavior will simplify fixing how KVM handles !visible
guest root gfns (immediately synthesizing a triple fault when loading the
root is architecturally wrong).

Link: https://lore.kernel.org/r/20230729005200.1057358-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2023-07-28 17:51:59 -07:00 committed by Paolo Bonzini
parent 2c6d4c27b9
commit b5b359ac30
1 changed files with 6 additions and 1 deletions
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7
arch/x86/kvm/mmu/paging_tmpl.h
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@ -361,6 +361,7 @@ retry_walk:
++walker->level;
do {
struct kvm_memory_slot *slot;
unsigned long host_addr;
pt_access = pte_access;
@ -391,7 +392,11 @@ retry_walk:
if (unlikely(real_gpa == INVALID_GPA))
return 0;
host_addr = kvm_vcpu_gfn_to_hva_prot(vcpu, gpa_to_gfn(real_gpa),
slot = kvm_vcpu_gfn_to_memslot(vcpu, gpa_to_gfn(real_gpa));
if (!kvm_is_visible_memslot(slot))
goto error;
host_addr = gfn_to_hva_memslot_prot(slot, gpa_to_gfn(real_gpa),
&walker->pte_writable[walker->level - 1]);
if (unlikely(kvm_is_error_hva(host_addr)))
goto error;