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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