What is the difference between syscall arguments and LSM hook events in Linux runtime monitoring?

Syscall arguments show what a process asked the kernel to do, while LSM hook events show what the kernel actually used during enforcement. That difference matters when paths are relative, files are linked, or arguments change during execution. For security monitoring, LSM hook data usually gives a more trustworthy basis for detection, policy decisions, and forensic analysis.

Syscall Arguments vs LSM Hook Events: What They Actually Represent

Syscall arguments are the user-space inputs a process supplied when it asked the kernel to perform an action. LSM hook events are the kernel-side security decision points that see the operation as it is enforced. The practical difference is that one reflects intent at the API boundary, while the other reflects the object, path, or context the kernel actually used.

This distinction shows up most clearly when the original argument is not the final object of enforcement. A relative path may be resolved against a current working directory, a symlink may be followed, or a value may be rewritten during execution before the kernel applies policy.

Why the Kernel View Is Often More Reliable for Detection

For runtime monitoring, the LSM hook is usually the stronger ground truth because it is tied to the enforcement path rather than the caller’s declared input. That makes it better suited for security decisions that depend on the real target, the real access path, and the real object touched by the kernel.

Syscall arguments still matter for reconstruction and triage. They show what the process attempted, which can help when you want to compare intent versus outcome, understand exploit attempts, or spot evasive behavior that relies on argument manipulation. But if the monitoring goal is policy enforcement or high-confidence file and process attribution, the hook view is normally the more trustworthy signal.

Linux runtime telemetry is strongest when you preserve both views and compare them. The argument stream helps explain the request, while the LSM event helps explain what actually happened after kernel resolution, normalization, and enforcement.

Where the Difference Changes Operational Decisions

Security teams should treat this as a source-of-truth issue, not just a logging preference. If an investigation depends on the exact object accessed, the event after kernel mediation should drive the primary conclusion, especially in cases involving path traversal, links, mount namespace effects, or late-binding changes.

For policy design, the distinction matters even more. Rules written against syscall arguments can miss the effective target or generate false confidence if the requested path is not the same as the enforced path. LSM-based telemetry is better aligned with decisions about allow, deny, alert, and forensic attribution because it tracks the kernel’s enforcement view.

That does not make syscall data useless. It is often the better evidence for attacker intent, application debugging, and understanding why a request was made in the first place. The best monitoring pipelines correlate both, then decide which one is authoritative for the specific use case.

Risk and Threat Considerations

Monitoring that relies only on syscall arguments can misread the effective target of access, especially when an attacker uses symbolic links, path races, or other resolution tricks to create a mismatch between requested and enforced objects. That can weaken detection, distort incident timelines, and produce weak forensic evidence.

Failure mechanism: The sensor records the caller’s declared input instead of the kernel-resolved object or security-relevant context, so enforcement and audit conclusions are based on an incomplete view.

Impact: Defenders can miss the real asset touched, overtrust the apparent path, or build detections that are easy to evade by changing how the kernel resolves the access.

Standards & Framework Alignment

This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.

MITRE ATT&CK addresses the attack and risk surface, while CIS Controls v8, NIST CSF 2.0 and NIST SP 800-53 Rev 5 set the governance and control requirements practitioners need to meet.

Framework	Control / Reference	Relevance
MITRE ATT&CK	T1036 — Masquerading	Path and object confusion often supports deceptive access behavior.
Recommendation — Correlate path-resolution mismatches with masquerading indicators in your detection workflow.
CIS Controls v8	CIS-8 — Audit Log Management	Runtime monitoring depends on logs that preserve the authoritative enforcement view.
Recommendation — Capture kernel-resolved security events to support trustworthy audit analysis.
NIST CSF 2.0	DE.CM-01 — Monitoring for Unauthorized Activities	The question is about which runtime telemetry is more reliable for detecting suspicious activity.
Recommendation — Prefer telemetry that reflects enforcement outcomes when monitoring for unauthorized activity.
NIST SP 800-53 Rev 5	AU-3 — Content of Audit Records	Audit records should capture the meaningful enforcement context, not only raw request inputs.
	SI-4 — System Monitoring	The topic is runtime monitoring and choosing the most trustworthy event source.
Recommendation — Record the resolved object and security context needed for forensic reconstruction. Tune monitoring to the kernel-side event source for higher-fidelity detection.

Practitioner Guidance

What to verify: For any high-value detection or forensic workflow, confirm whether the event source captures the kernel-resolved target, not just the raw syscall argument. If the answer is no, treat the telemetry as intent data rather than authoritative enforcement evidence.

Decision rule: Use syscall arguments when you need request context, but base policy assertions, object attribution, and post-incident evidence on the kernel-side event when both are available.

Practitioner takeaway: The core judgment is to separate requested action from enforced action, then choose the kernel’s resolved view whenever correctness depends on the actual object or access path.