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KVM: SVM: avoid infinite loop on NPF from bad address

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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>
This commit is contained in:
Paolo Bonzini 2020-04-17 12:21:06 -04:00
parent 997b7e9899
commit e72436bc3a
2 changed files with 8 additions and 0 deletions
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7
arch/x86/kvm/svm/svm.c
View File

@ -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.
*

1
virt/kvm/kvm_main.c
View File

@ -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)
{