From: Sean Christopherson <seanjc@xxxxxxxxxx> 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@xxxxxxxxxx> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx> Message-ID: <20240228024147.41573-17-seanjc@xxxxxxxxxx> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> --- arch/x86/kvm/mmu/mmu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index d717d60c6f19..510eb1117012 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4425,7 +4425,7 @@ 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); /* -- 2.43.0
