KVM: nVMX: Fix kernel info-leak when enabling KVM_CAP_HYPERV_ENLIGHTENED_VMCS more than once
Consider the case that userspace enables KVM_CAP_HYPERV_ENLIGHTENED_VMCS twice: 1) kvm_vcpu_ioctl_enable_cap() is called to enable KVM_CAP_HYPERV_ENLIGHTENED_VMCS which calls nested_enable_evmcs(). 2) nested_enable_evmcs() sets enlightened_vmcs_enabled to true and fills vmcs_version which is then copied to userspace. 3) kvm_vcpu_ioctl_enable_cap() is called again to enable KVM_CAP_HYPERV_ENLIGHTENED_VMCS which calls nested_enable_evmcs(). 4) This time nested_enable_evmcs() just returns 0 as enlightened_vmcs_enabled is already true. *Without filling vmcs_version*. 5) kvm_vcpu_ioctl_enable_cap() continues as usual and copies *uninitialized* vmcs_version to userspace which leads to kernel info-leak. Fix this issue by simply changing nested_enable_evmcs() to always fill vmcs_version output argument. Even when enlightened_vmcs_enabled is already set to true. Note that SVM's nested_enable_evmcs() should not be modified because it always returns a non-zero value (-ENODEV) which results in kvm_vcpu_ioctl_enable_cap() skipping the copy of vmcs_version to userspace (as it should). Fixes: 57b119da ("KVM: nVMX: add KVM_CAP_HYPERV_ENLIGHTENED_VMCS capability") Reported-by: syzbot+cfbc368e283d381f8cef@syzkaller.appspotmail.com Reviewed-by: NKrish Sadhukhan <krish.sadhukhan@oracle.com> Reviewed-by: NVitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: NLiran Alon <liran.alon@oracle.com> Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
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