From e72436bc3a5206f95bb384e741154166ddb3202e Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Fri, 17 Apr 2020 12:21:06 -0400 Subject: [PATCH] KVM: SVM: avoid infinite loop on NPF from bad address When a nested page fault is taken from an address that does not have a memslot associated to it, kvm_mmu_do_page_fault returns RET_PF_EMULATE (via mmu_set_spte) and kvm_mmu_page_fault then invokes svm_need_emulation_on_page_fault. The default answer there is to return false, but in this case this just causes the page fault to be retried ad libitum. Since this is not a fast path, and the only other case where it is taken is an erratum, just stick a kvm_vcpu_gfn_to_memslot check in there to detect the common case where the erratum is not happening. This fixes an infinite loop in the new set_memory_region_test. Signed-off-by: Paolo Bonzini --- arch/x86/kvm/svm/svm.c | 7 +++++++ virt/kvm/kvm_main.c | 1 + 2 files changed, 8 insertions(+) diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index a6f4e1b..eb95283 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -3838,6 +3838,13 @@ static bool svm_need_emulation_on_page_fault(struct kvm_vcpu *vcpu) bool is_user = svm_get_cpl(vcpu) == 3; /* + * If RIP is invalid, go ahead with emulation which will cause an + * internal error exit. + */ + if (!kvm_vcpu_gfn_to_memslot(vcpu, kvm_rip_read(vcpu) >> PAGE_SHIFT)) + return true; + + /* * Detect and workaround Errata 1096 Fam_17h_00_0Fh. * * Errata: diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index e2f60e3..e7436d0 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1602,6 +1602,7 @@ struct kvm_memory_slot *kvm_vcpu_gfn_to_memslot(struct kvm_vcpu *vcpu, gfn_t gfn { return __gfn_to_memslot(kvm_vcpu_memslots(vcpu), gfn); } +EXPORT_SYMBOL_GPL(kvm_vcpu_gfn_to_memslot); bool kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn) { -- 2.7.4