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 a…

Overview

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.

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.