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 <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index a6f4e1b..eb95283 100644 (file)
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3837,6 +3837,13 @@ static bool svm_need_emulation_on_page_fault(struct kvm_vcpu *vcpu)
        bool smap = cr4 & X86_CR4_SMAP;
        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.
         *

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index e2f60e3..e7436d0 100644 (file)
--- 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)
 {