A research team from the CISPA Helmholtz Center for Information Security in Germany has uncovered a critical architectural bug, named GhostWrite, in the RISC-V CPUs XuanTie C910 and C920 produced by Chinese chip manufacturer T-Head. This vulnerability, embedded directly in the hardware, allows unprivileged attackers, even those with limited access, to read and write any part of the device’s memory and control peripheral devices like network cards. GhostWrite effectively neutralizes the CPU’s security features and poses a significant threat since it cannot be rectified without disabling approximately half of the CPU’s functionality.
The flaw originates from faulty instructions in the CPU’s vector extension, which is designed to handle larger data values than the standard Instruction Set Architecture (ISA). By operating directly on physical memory rather than virtual memory, these instructions can bypass the usual process isolation enforced by both the operating system and hardware. Consequently, an attacker could exploit this loophole to gain unrestricted access to any memory location and leak sensitive data, including passwords, from the device.
Researchers emphasized the reliability and speed of the GhostWrite attack, stating it is deterministic and executes within microseconds. They noted that even robust security measures like Docker containerization or sandboxing cannot thwart this vulnerability. Additionally, attackers can hijack hardware devices using memory-mapped input/output (MMIO) to send unauthorized commands, further exacerbating the risk posed by this bug.
The recommended countermeasure to mitigate GhostWrite involves disabling the entire vector functionality of the CPU, which, while effective, severely degrades performance by eliminating about 50% of the instruction set. Disabling these vector instructions may slow down applications that depend on parallel processing and handling large datasets. This disclosure comes amidst other recent findings, including vulnerabilities in Qualcomm’s Adreno GPU and AMD processors, underscoring ongoing security challenges in the semiconductor industry and the critical need for continuous monitoring and updates to hardware security protocols.
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