Commit e1779c27 authored by Maxim Levitsky's avatar Maxim Levitsky Committed by Paolo Bonzini
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KVM: x86: nSVM: fix potential NULL derefernce on nested migration 



Turns out that due to review feedback and/or rebases
I accidentally moved the call to nested_svm_load_cr3 to be too early,
before the NPT is enabled, which is very wrong to do.

KVM can't even access guest memory at that point as nested NPT
is needed for that, and of course it won't initialize the walk_mmu,
which is main issue the patch was addressing.

Fix this for real.

Fixes: 232f75d3 ("KVM: nSVM: call nested_svm_load_cr3 on nested state load")
Cc: stable@vger.kernel.org

Signed-off-by: default avatarMaxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220207155447.840194-3-mlevitsk@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent c53bbe21

arch/x86/kvm/svm/nested.c

+14 −12
Original line number Diff line number Diff line
@@ -1457,18 +1457,6 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu, 
	    !__nested_vmcb_check_save(vcpu, &save_cached))

		goto out_free;



	/*

	 * While the nested guest CR3 is already checked and set by

	 * KVM_SET_SREGS, it was set when nested state was yet loaded,

	 * thus MMU might not be initialized correctly.

	 * Set it again to fix this.

	 */



	ret = nested_svm_load_cr3(&svm->vcpu, vcpu->arch.cr3,

				  nested_npt_enabled(svm), false);

	if (WARN_ON_ONCE(ret))

		goto out_free;





	/*

	 * All checks done, we can enter guest mode. Userspace provides
@@ -1494,6 +1482,20 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu, 


	svm_switch_vmcb(svm, &svm->nested.vmcb02);

	nested_vmcb02_prepare_control(svm);



	/*

	 * While the nested guest CR3 is already checked and set by

	 * KVM_SET_SREGS, it was set when nested state was yet loaded,

	 * thus MMU might not be initialized correctly.

	 * Set it again to fix this.

	 */



	ret = nested_svm_load_cr3(&svm->vcpu, vcpu->arch.cr3,

				  nested_npt_enabled(svm), false);

	if (WARN_ON_ONCE(ret))

		goto out_free;





	kvm_make_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu);

	ret = 0;

out_free: