CVE-2024-43865 in Linux
Summary
by MITRE • 08/21/2024
In the Linux kernel, the following vulnerability has been resolved:
s390/fpu: Re-add exception handling in load_fpu_state()
With the recent rewrite of the fpu code exception handling for the lfpc instruction within load_fpu_state() was erroneously removed.
Add it again to prevent that loading invalid floating point register values cause an unhandled specification exception.
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Analysis
by VulDB Data Team • 02/17/2026
The vulnerability identified as CVE-2024-43865 represents a critical regression in the Linux kernel's floating point unit handling specifically on s390 architecture systems. This issue stems from a code modification that inadvertently eliminated essential exception handling mechanisms within the load_fpu_state() function, which is responsible for managing the loading of floating point control registers during processor state transitions. The s390 architecture, being a mainframe instruction set architecture, requires precise handling of floating point operations due to its complex instruction set and the critical nature of mainframe computing environments where system stability and data integrity are paramount.
The technical flaw manifests in the removal of exception handling for the lfpc (load floating point control) instruction within the load_fpu_state() function, which is a fundamental operation in the floating point unit management subsystem. When invalid floating point register values are loaded into the processor's floating point control registers, the absence of proper exception handling causes the system to encounter an unhandled specification exception rather than gracefully managing the error condition. This regression directly violates the expected behavior of the kernel's floating point unit subsystem and can lead to unpredictable system behavior when floating point operations are performed on s390 systems. The issue falls under CWE-248, which describes an "Uncaught Exception" in software systems, and represents a failure in proper error recovery mechanisms within a critical system component.
The operational impact of this vulnerability extends beyond simple system instability to potentially compromise entire mainframe environments where the Linux kernel is deployed. On s390 systems, which are commonly used in enterprise data centers, financial services, and government applications, the failure to properly handle floating point exceptions can result in system crashes, data corruption, or denial of service conditions that could affect mission-critical applications. The vulnerability is particularly concerning because it affects the kernel's ability to maintain system integrity when processing floating point operations, which are fundamental to many business-critical workloads including database operations, scientific computing, and financial transaction processing. Attackers could potentially exploit this vulnerability to cause system instability or create conditions that might facilitate further attacks, making this a significant concern for organizations relying on mainframe computing environments.
The recommended mitigation strategy involves applying the kernel patch that reintroduces the missing exception handling for the lfpc instruction within the load_fpu_state() function. System administrators should prioritize updating their s390-based systems to the patched kernel versions as soon as possible, particularly in production environments where mainframe stability is crucial. Organizations should also implement monitoring systems to detect potential floating point exception conditions and maintain comprehensive backup and recovery procedures to address any system instability that might occur during the patching process. The fix aligns with ATT&CK technique T1490, which involves creating or manipulating system processes to achieve persistence or maintain access, as proper exception handling prevents unauthorized system modifications through error conditions. Additionally, the remediation should include verification testing to ensure that floating point operations behave correctly after patching and that no regressions have been introduced in other kernel subsystems that might interact with the floating point unit management code.