## 6 Results and Discussion
This stack encompasses not only software and operating systems but also hypervisors and the virtualization layer. However, it is essential that the TPM emulator remains in a state of verified integrity, ensuring the trustworthiness of the information it provides. To achieve this goal, access control and integrity monitoring mechanisms--such as SELinux, IMA, and EVM (Extended Verification Module)--can be employed, along with other approaches that enable the protection, verification, and assurance that the emulator software has not been improperly modified. Therefore, we assume that, if the emulator's integrity is compromised, the machine will not be included in the hyperconverged TPM pool. Figure 12: Estimated mean memory utilization of host 1 with 95% confidence interval. Figure 13: Estimated mean memory utilization of host 2 with 95% confidence interval. One of the main considerations when using a vTPM concerns the protection of its persistent state, namely the NVRAM. Unlike conventional TPMs, which physically embed NVRAM in the hardware, a vTPM typically uses a disk file to simulate NVRAM [12]. Protecting the confidential information stored in this file is critically important due to its sensitive nature. Once inside the environment, the attacker can perform various malicious actions that compromise the integrity of the data within the vTPM instances. The adversary may gain full control over read and write operations, as well as the update and binding of the NVRAM [11; 12]. These actions can be carried out by exploiting several potential threats in the system, among which the following stand out:  
* **Backdoors and Unpatched Vulnerabilities**: Backdoors are software mechanisms or capabilities intentionally inserted by developers for various purposes, often without official documentation and with restricted knowledge, posing a security threat by enabling unauthorized access or manipulation of systems. Unpatched vulnerabilities, on the other hand, are unintentional flaws in software that can be exploited by attackers, presenting significant security risks if not promptly addressed through fixes or patches [61]. Both issues can compromise the integrity and security of the vTPM, requiring prompt action to mitigate their impact [17]. These threats become especially critical in environments with high virtual machine density, where there is little or no governance over the software executed by users. * **Privilege Escalation**: In the context of vTPMs, privilege escalation may allow an attacker to leverage elevated privileges to perform unauthorized modifications to the vTPM's persistent state, such as a rollback attack [11; 12]. * **Hypervisor Vulnerabilities**: Vulnerabilities in hypervisor software can be exploited to gain unauthorized access to VM control and the associated NVRAM. Attackers may leverage flaws that allow them to escape the VM's isolated environment, compromise the hypervisor, and consequently access and modify the NVRAM [62] belonging to another user, as seen in binding attacks. Most of the approaches proposed in the literature focus on the confidentiality of the vTPM and NVRAM, utilizing encryption mechanisms and vTPM key anchoring [5; 6; 15]. However, recently, threat scenarios have emerged that primarily compromise the integrity of the vTPM:  
* **Scenario 01: Rollback Attack**: Since NVRAM typically resides in a storage system vulnerable to compromise, an attacker may take control of the NVRAM and make unauthorized modifications, including tampering with the NVRAM files. For example, the attacker could prepare a copy of the persistent state in advance and later replace the stored version with this state. This attack is known as a rollback [11; 12]. The main consequence of this attack is the lack of a guarantee that the persistent state is always up to date as the attacker has the ability to replace the NVRAM file with an earlier version. The attacker may have various ways to modify the version of the NVRAM.