Commit d6e656cd authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
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KVM: nVMX: WARN on any attempt to allocate shadow VMCS for vmcs02 



WARN if KVM attempts to allocate a shadow VMCS for vmcs02.  KVM emulates
VMCS shadowing but doesn't virtualize it, i.e. KVM should never allocate
a "real" shadow VMCS for L2.

The previous code WARNed but continued anyway with the allocation,
presumably in an attempt to avoid NULL pointer dereference.
However, alloc_vmcs (and hence alloc_shadow_vmcs) can fail, and
indeed the sole caller does:

	if (enable_shadow_vmcs && !alloc_shadow_vmcs(vcpu))
		goto out_shadow_vmcs;

which makes it not a useful attempt.

Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20220125220527.2093146-1-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 4cf3d3eb

arch/x86/kvm/vmx/nested.c

+12 −10
Original line number Diff line number Diff line
@@ -4851,18 +4851,20 @@ static struct vmcs *alloc_shadow_vmcs(struct kvm_vcpu *vcpu) 
	struct loaded_vmcs *loaded_vmcs = vmx->loaded_vmcs;



	/*

	 * We should allocate a shadow vmcs for vmcs01 only when L1

	 * executes VMXON and free it when L1 executes VMXOFF.

	 * As it is invalid to execute VMXON twice, we shouldn't reach

	 * here when vmcs01 already have an allocated shadow vmcs.

	 */

	WARN_ON(loaded_vmcs == &vmx->vmcs01 && loaded_vmcs->shadow_vmcs);

	 * KVM allocates a shadow VMCS only when L1 executes VMXON and frees it

	 * when L1 executes VMXOFF or the vCPU is forced out of nested

	 * operation.  VMXON faults if the CPU is already post-VMXON, so it

	 * should be impossible to already have an allocated shadow VMCS.  KVM

	 * doesn't support virtualization of VMCS shadowing, so vmcs01 should

	 * always be the loaded VMCS.

	 */

	if (WARN_ON(loaded_vmcs != &vmx->vmcs01 || loaded_vmcs->shadow_vmcs))

		return loaded_vmcs->shadow_vmcs;



	if (!loaded_vmcs->shadow_vmcs) {

	loaded_vmcs->shadow_vmcs = alloc_vmcs(true);

	if (loaded_vmcs->shadow_vmcs)

		vmcs_clear(loaded_vmcs->shadow_vmcs);

	}



	return loaded_vmcs->shadow_vmcs;

}