CVE-2022-34640 in CVA6
Summary
by MITRE • 07/19/2022
The *tval of ecall/ebreak in CVA6 commit d315ddd0f1be27c1b3f27eb0b8daf471a952299a was discovered to be incorrect.
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Analysis
by VulDB Data Team • 08/06/2022
The vulnerability identified as CVE-2022-34640 affects the CVA6 RISC-V processor implementation, specifically concerning the handling of ecall and ebreak instructions within the processor's exception handling mechanism. This issue resides in the commit d315ddd0f1be27c1b3f27eb0b8daf471a952299a of the CVA6 repository, indicating a flaw in the processor's trap vector address calculation logic. The problem manifests in the incorrect calculation of the tval field, which is a critical component in the RISC-V exception handling framework that provides additional context information about the cause of an exception. When ecall and ebreak instructions are executed, the processor should correctly populate the tval register with relevant exception information, but this implementation contains a bug that results in incorrect values being stored.
The technical flaw stems from an error in the processor's trap handling code where the calculation of the tval value fails to properly account for the instruction address or the specific exception context during ecall and ebreak execution. This misconfiguration directly impacts the processor's ability to provide accurate exception context to software running on the system. The tval field serves as a crucial diagnostic element in RISC-V architectures, allowing software to determine the precise cause and location of exceptions, particularly when debugging or handling system calls. When this field contains incorrect data, it undermines the reliability of exception handling mechanisms and can lead to unpredictable behavior in software that depends on accurate exception information for proper operation.
The operational impact of this vulnerability extends beyond simple incorrect data reporting, as it can compromise the integrity of system-level operations that rely on proper exception handling. In embedded systems and processor implementations where CVA6 is deployed, incorrect tval values can cause software to make erroneous decisions based on faulty exception information, potentially leading to system instability, incorrect error recovery, or even security vulnerabilities if the faulty exception handling affects privilege level transitions. The vulnerability particularly affects systems where precise exception context is critical for maintaining system security and reliability, such as in safety-critical applications or systems implementing secure execution environments.
This vulnerability aligns with CWE-248, which addresses "Uncaught Exception" in software systems, and can be mapped to ATT&CK technique T1059.001 for "Command and Scripting Interpreter: PowerShell" in scenarios where the faulty exception handling might be exploited to bypass security controls. Mitigation strategies should include updating to a patched version of the CVA6 implementation where the tval calculation has been corrected, implementing additional software-level validation of exception contexts, and conducting thorough testing of exception handling pathways in affected systems. Organizations should also consider implementing runtime monitoring to detect anomalous exception behavior that might indicate the presence of this vulnerability, particularly in systems where precise exception context is critical for maintaining system integrity and security posture.