QEMU Root Shell Access Vulnerability
AMD ID: AMD-SB-3012
Potential Impact: Guest OS Root Shell Access from Malicious Host
Severity: N/A
Summary
Researchers from the University of Tokyo shared with AMD a paper titled “A Root Shell Access Vulnerability in QEMU for AMD SEV-SNP Confidential Virtual Machines.”
The research paper reports that a vulnerability present in the AMD development Quick EMUlator (QEMU) for SEV-SNP VMs could allow a malicious host to access the guest OS's root shell.
The researchers note that this vulnerability exists in the measured direct boot, where the attestation report includes the hashes of the kernel, the initrd (initial ramdisk), and kernel arguments but doesn’t include the hash of ACPI tables. Therefore, the malicious host can place maliciously crafted ACPI Machine Language (AML) code into the guest and cause it to be executed within the guest, modifying memory to execute a root shell.
The paper describes several potential mitigations for this vulnerability such as disabling ACPI, Randomizing initrd (initial ram disk) address, Measuring ACPI data, and using virtual TPMs.
AMD confirms that the code against which the issue is reported is now available within the upstream QEMU. This is a vulnerability in the guest Linux® kernel having to accept and trust arbitrary ACPI data from a hypervisor and hence any hypervisor or VMM like QEMU would be impacted as well.
Affected Products
QEMU for AMD SEV-SNP confidential virtual machines (https://github.com/amdese/qemu/tree/snp-latest)
Mitigation
AMD recommends the measurement or sanitization of ACPI tables, such as the use of a vTPM. Preview code for confidential compute enabled vTPM support can be found at the link below.
Coconut-SVSM: https://github.com/coconut-svsm
Acknowledgement
AMD thanks Takahiro Shinagawa, Manami Mori, and Takaaki Fukai from the University of Tokyo for reporting this issue and engaging in coordinated vulnerability disclosure.
Revisions
Revision Date |
Description |
| 2024-12-09 | Initial publication |
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