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

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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 <dmatlack@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Message-ID: <20240228024147.41573-17-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2024-02-27 18:41:47 -08:00 committed by Paolo Bonzini
parent f3310e622f
commit 2b1f435505
1 changed files with 1 additions and 1 deletions
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2
arch/x86/kvm/mmu/mmu.c
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@ -4424,7 +4424,7 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
if (unlikely(is_error_pfn(fault->pfn)))
return kvm_handle_error_pfn(vcpu, fault);
if (WARN_ON_ONCE(!fault->slot))
if (WARN_ON_ONCE(!fault->slot || is_noslot_pfn(fault->pfn)))
return kvm_handle_noslot_fault(vcpu, fault, access);
/*