In the Linux kernel, the following vulnerability has been resolved: arm64: hibernate: mask DAIF...

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.