一种基于影子页表+的软件型vTPM密钥秘密信息保护方案

Software vTPM Key Information Protection Scheme Based on Shadow Page Table Plus

由于TPM是一块资源受限的硬件芯片,在可信虚拟平台上所有用户虚拟机都通过共享TPM方式来实现可信计算的功能是不现实的.因此,当前不少虚拟平台在对TPM虚拟化时采用软件仿真方式,但现有虚拟机环境中的许多恶意攻击均能窃取和破坏此类vTPM运行时的密钥秘密信息,特别在全虚拟化和硬件虚拟化平台环境中,整个虚拟机均处于VMM的用户空间中, vTPM的密钥秘密信息更容易遭到攻击,这将严重影响虚拟机和vTPM的安全.为此,本文提出了一种基于影子页表+的软件型vTPM密钥秘密信息保护方案.该方案主要是在全虚拟化或硬件虚拟化平台中通过新增影子页表管理模块MMU-vTPM来保护vTPM的密钥秘密信息,该管理模块通过对vTPM密钥私有内存页表的访问控制来阻止其他进程非法访问和破坏vTPM密钥秘密信息私有内存.而且为了防止恶意用户对MMU-vTPM模块进行篡改,采用TPM的静态度量机制和动态度量机制对该模块进行完整性保护.最后,基于Xen实现了该方案.测试结果表明,该方案能够在保证vTPM的vEK和v SRK等关键密钥秘密信息的安全性,而且不会带来严重的性能损失.

Because of the limit of hardware resources,it is impossible to share the TPM function for all the virtual machines on the trusted virtual platform.Therefore,many of the virtual machines use the emulator to virtualized the TPM,i.e.,using the software vTPM to simulate the function of TPM.However,there are many attacks in the virtual machine environment,where it is easy to steal and destroy the keys and certificates which exist in the running space of the vTPM,especially in the full virtualization platform and hardware assisted virtualization platform,the keys of vTPM will be more vulnerable against attacks due to the whole virtual machine being in the user space of VMM,this will seriously affect the security of the virtual machine and vTPM.In this study,a software vTPM key protection scheme based on shadow page table plus is proposed.In this scheme,through a new added shadow page table management module which called MMU-vTPM to protect the keys and certificates in the full virtualization platform or hardware virtualization platform,the MMU-vTPM will prevent other processes to access and damage the memory of the private vTPM keys by monitoring the page table access control.Moreover,in order to prevent the tamper of MMU-vTPM module from the malicious users,the static integrity measurement and dynamic integrity measurement are used to protect the integrity of MMU-vTPM module.At last,an implement of the proposed scheme is given based on the Xen virtualization platform.The test results show that the scheme can ensure the security of the vEK,vSRK,and other secret information of the vTPM,and do not seriously affect the performance.