CVE-2024-40944 in Linux
Summary
by MITRE • 07/12/2024
In the Linux kernel, the following vulnerability has been resolved:
x86/kexec: Fix bug with call depth tracking
The call to cc_platform_has() triggers a fault and system crash if call depth tracking is active because the GS segment has been reset by load_segments() and GS_BASE is now 0 but call depth tracking uses per-CPU variables to operate.
Call cc_platform_has() earlier in the function when GS is still valid.
[ bp: Massage. ]
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Analysis
by VulDB Data Team • 10/07/2025
The vulnerability identified as CVE-2024-40944 represents a critical flaw in the Linux kernel's x86 kexec implementation that can lead to system crashes and potential denial of service conditions. This issue specifically affects the call depth tracking mechanism within the kernel's architecture and occurs during the execution of the cc_platform_has() function. The vulnerability manifests when the system attempts to perform a kexec operation, which is a mechanism for loading and executing a new kernel while the current kernel is running, commonly used for system updates and maintenance operations. The flaw is particularly concerning because it directly impacts the kernel's ability to handle platform-specific security features during critical system transitions.
The technical root cause of this vulnerability lies in the improper handling of segment register management during the kexec process. When load_segments() is executed, it resets the GS segment, setting GS_BASE to zero, which subsequently breaks the call depth tracking functionality. This occurs because the call depth tracking mechanism relies on per-CPU variables that depend on the GS segment being properly initialized. The cc_platform_has() function, which checks for platform-specific capabilities, triggers a fault when executed after the segment reset because it attempts to access these per-CPU variables through the now-invalid GS segment. This architectural mismatch between segment register management and per-CPU variable access creates a direct path to system instability and potential kernel crashes.
The operational impact of this vulnerability extends beyond simple system crashes, as it can severely compromise the reliability of systems that depend on kexec operations for updates, maintenance, or failover scenarios. Systems administrators who rely on automated patching processes or frequent kernel updates may experience unexpected system downtime when this vulnerability is triggered. The flaw particularly affects server environments and embedded systems where kexec is commonly used for seamless kernel transitions. From an attack perspective, this vulnerability could be exploited by malicious actors to cause denial of service conditions, potentially leading to extended system outages that could impact availability and service continuity. The vulnerability's impact is amplified in environments where kexec is frequently utilized, such as in cloud infrastructure, containerized environments, and systems requiring high availability.
The fix implemented for this vulnerability addresses the core issue by repositioning the cc_platform_has() function call to occur earlier in the execution sequence, before the load_segments() function resets the GS segment. This approach ensures that the per-CPU variables required for call depth tracking remain accessible throughout the critical execution path. The solution follows established kernel development practices for managing segment register states and maintains compatibility with existing platform-specific security features. From a security standards perspective, this vulnerability aligns with CWE-248, which covers "Uncaught Exception" and relates to improper handling of exceptional conditions in software systems. The fix also demonstrates adherence to ATT&CK framework concept T1499.004, which addresses "Virtualization/Sandbox Evasion" through proper system state management. The resolution emphasizes the importance of careful segment management during critical kernel operations and reinforces the need for proper temporal ordering of system initialization routines to prevent state corruption that could lead to system instability.