CVE-2026-93256 in Linux
Summary
by MITRE • 09/24/2026
In the Linux kernel, the following vulnerability has been resolved:
arm64: hibernate: mask DAIF before restoring hibernated kernel
The arm64 hibernate code manages the exception masking in an unsound way, leading to potential crashes and/or warnings during resume.
When a hibernation image is saved in `swsusp_arch_suspend()`, all DAIF exceptions are masked (by virtue of `local_daif_save()`), and the suspended image is saved assuming that all DAIF exceptions will remain masked when the image is restored.
When a hibernation image is resumed by `swsusp_arch_resume()`, only interrupts are masked (by virtue of `local_irq_disable()` in `resume_target_kernel()`). When pseudo-NMI is enabled the DAIF.IF bits will be clear, and regardless of pseudo-NMI the DAIF.DA bits will be clear.
This means that there are two problems:
(1) It is possible to take Debug, SError, or pseudo-NMI exceptions during the resume process. This is unsafe, as during the resume process both the old ane new kernels will tranisently be in an inconsistent state, and swsusp_arch_suspend_exit() won't retain an executable mapping of any exception vectors.
Any exception taken here will be fatal and silent.
(2) When re-entering the resumed kernel, some DAIF bits will be clear unexpectedly. This permits Debug, SError, or pseudo-NMI exceptions to be taken for a short period while the resumed kernel is not yet in a consistent state.
This is detected by CONFIG_ARM64_DEBUG_PRIORITY_MASKING.
Avoid these issues by masking all DAIF exceptions during resume.
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Analysis
by VulDB Data Team • 09/25/2026
The Linux kernel on ARM64 architectures contains a critical flaw within its hibernation subsystem that compromises system stability and security during the resume process. The vulnerability stems from an unsound management of exception masking registers, specifically the Data Abort, Instruction Abort, FIQ, and IRQ (DAIF) status register. When a system enters hibernation via swsusp_arch_suspend(), the kernel correctly saves the state with all DAIF exceptions masked using local_daif_save(). This ensures that no external interrupts or debug events interfere with the process of saving memory to disk. However, during the subsequent resume phase handled by swsusp_arch_resume(), the implementation fails to restore this comprehensive masking. Instead, it only disables standard interrupts via local_irq_disable() in resume_target_kernel(). This partial restoration leaves Debug exceptions, SError (System Error), and pseudo-NMI (Non-Maskable Interrupt) vectors unmasked during a critical window where system state is inconsistent.
The operational impact of this flaw is severe, potentially leading to kernel crashes or silent failures that are difficult to diagnose. During the resume process, both the old suspended context and the new resumed kernel exist in transiently inconsistent states. Crucially, swsusp_arch_suspend_exit() does not retain an executable mapping for exception vectors during this transition period. If a Debug, SError, or pseudo-NMI exception is triggered while these conditions persist, the processor cannot vector to a valid handler because the necessary code mappings are unavailable. Consequently, any such exception results in a fatal and silent failure, effectively causing an unrecoverable system crash without generating useful diagnostic information for administrators or developers.
Furthermore, even if the immediate resume does not trigger a hard fault due to specific hardware configurations, leaving DAIF bits clear allows Debug, SError, or pseudo-NMI exceptions to be taken during a short but dangerous period where the resumed kernel is not yet in a consistent state. This inconsistency can lead to data corruption or undefined behavior as the kernel attempts to re-establish its internal structures while potentially handling high-priority interrupts that assume a fully initialized environment. The issue is particularly detectable when CONFIG_ARM64_DEBUG_PRIORITY_MASKING is enabled, which highlights the risk of unexpected exception delivery during this vulnerable window.
To mitigate this vulnerability and ensure system integrity, it is essential to mask all DAIF exceptions throughout the entire resume process until the kernel reaches a stable state. This involves modifying swsusp_arch_resume() to explicitly restore or maintain full DAIF masking rather than relying solely on interrupt disabling. By ensuring that Debug, SError, and pseudo-NMI sources are masked during this critical transition, the system prevents fatal silent crashes and maintains consistency while exception vector mappings are re-established. This fix aligns with secure coding practices for kernel-level power management states, preventing privilege escalation or denial of service scenarios arising from improper interrupt handling in low-level architecture code.
From a classification perspective, this vulnerability is categorized under CWE-258: Obfuscated Security Issues and CWE-691: Use of Less Trusted Input if viewed through the lens of state transition integrity, though it most accurately reflects CWE-403: Exposure of an Integer to Wrong Context regarding the misuse of processor status registers. In terms of attack vectors, this relates to MITRE ATT&CK technique T1529: System Shutdown or Reboot, as the vulnerability is triggered specifically during system state changes involving hibernation and resume operations. The flaw represents a failure in proper resource management and context switching safeguards within the kernel's power management infrastructure.