User mode vs. kernel mode: OSes explained | TechTarget

▤ Summary

The 2024 CrowdStrike outage, which rendered millions of Windows machines inoperable, was precipitated by security software that malfunctioned while running in kernel mode. User mode is an OS state with restricted access to the computer systems hardware and resources. Programs that run in kernel mode include the OS itself, process-related code and some security software. System call instructions have memory protections that make them unmodifiable or readable by user mode programs. One notable example of this is CrowdStrikes Falcon sensor, which regularly publishes content updates to the kernel to help the software detect new threats.

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