Commit 232f75d3 authored by Maxim Levitsky's avatar Maxim Levitsky Committed by Paolo Bonzini
Browse files

KVM: nSVM: call nested_svm_load_cr3 on nested state load 



While KVM's MMU should be fully reset by loading of nested CR0/CR3/CR4
by KVM_SET_SREGS, we are not in nested mode yet when we do it and therefore
only root_mmu is reset.

On regular nested entries we call nested_svm_load_cr3 which both updates
the guest's CR3 in the MMU when it is needed, and it also initializes
the mmu again which makes it initialize the walk_mmu as well when nested
paging is enabled in both host and guest.

Since we don't call nested_svm_load_cr3 on nested state load,
the walk_mmu can be left uninitialized, which can lead to a NULL pointer
dereference while accessing it if we happen to get a nested page fault
right after entering the nested guest first time after the migration and
we decide to emulate it, which leads to the emulator trying to access
walk_mmu->gva_to_gpa which is NULL.

Therefore we should call this function on nested state load as well.

Suggested-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210401141814.1029036-3-mlevitsk@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 8486039a

arch/x86/kvm/svm/nested.c

+22 −18
Original line number Diff line number Diff line
@@ -215,24 +215,6 @@ static bool nested_svm_vmrun_msrpm(struct vcpu_svm *svm) 
	return true;

}



static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)

{

	struct vcpu_svm *svm = to_svm(vcpu);



	if (WARN_ON(!is_guest_mode(vcpu)))

		return true;



	if (!nested_svm_vmrun_msrpm(svm)) {

		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;

		vcpu->run->internal.suberror =

			KVM_INTERNAL_ERROR_EMULATION;

		vcpu->run->internal.ndata = 0;

		return false;

	}



	return true;

}



static bool nested_vmcb_check_controls(struct vmcb_control_area *control)

{

	if (CC(!vmcb_is_intercept(control, INTERCEPT_VMRUN)))
@@ -1330,6 +1312,28 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu, 
	return ret;

}



static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)

{

	struct vcpu_svm *svm = to_svm(vcpu);



	if (WARN_ON(!is_guest_mode(vcpu)))

		return true;



	if (nested_svm_load_cr3(&svm->vcpu, vcpu->arch.cr3,

				nested_npt_enabled(svm)))

		return false;



	if (!nested_svm_vmrun_msrpm(svm)) {

		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;

		vcpu->run->internal.suberror =

			KVM_INTERNAL_ERROR_EMULATION;

		vcpu->run->internal.ndata = 0;

		return false;

	}



	return true;

}



struct kvm_x86_nested_ops svm_nested_ops = {

	.check_events = svm_check_nested_events,

	.triple_fault = nested_svm_triple_fault,