OS Security Principles
Learn the fundamental principles that guide secure operating system design and implementation.
Design Principles
Security Goals
Trade-offs
Operating system security is built on fundamental principles including least privilege, defense in depth, fail-safe defaults, economy of mechanism, complete mediation, and separation of privilege. These principles guide all security design decisions.
# OS Security Principles
os_security_principles = {
"least_privilege": {
"definition": "Grant minimum access rights necessary for task completion",
"implementation": ["User accounts", "Process privileges", "Service accounts"],
"benefits": ["Limits damage from compromise", "Reduces attack surface"],
"challenges": ["Usability vs security", "Privilege escalation needs"]
},
"defense_in_depth": {
"definition": "Multiple layers of security controls",
"layers": ["Hardware", "Kernel", "System services", "Applications"],
"examples": ["Firewall + antivirus + access controls", "Authentication + authorization + auditing"],
"advantage": "Single point of failure prevention"
},
"fail_safe_defaults": {
"definition": "Default to secure state when system fails",
"examples": ["Deny access by default", "Secure boot", "Default deny firewall rules"],
"principle": "Explicit grant rather than explicit deny"
},
"complete_mediation": {
"definition": "Check every access to every object",
"implementation": ["Reference monitor", "Access control checks"],
"requirements": ["No bypass", "Tamper-proof", "Verifiable"]
}
}
Security Architecture
Understand how security is integrated into operating system architecture and design.
Key Architecture Components:
• Trusted Computing Base (TCB): Security-critical components
• Reference Monitor: Mediates all access decisions
• Security Kernel: Core security functionality
• Security Perimeter: Boundary between trusted and untrusted
• Security Policy: Rules governing system behavior
Architecture Trade-offs:
Security architecture involves balancing security, performance, and usability. More security often means complexity, which can reduce performance and usability while potentially introducing new vulnerabilities.
# OS Security Architecture
security_architecture = {
"trusted_computing_base": {
"definition": "Set of all hardware, firmware, and software critical to security",
"components": ["Hardware", "Microcode", "OS kernel", "Security modules"],
"properties": ["Small size", "Well-defined", "Verified"],
"goal": "Minimize attack surface"
},
"reference_monitor": {
"definition": "Abstract machine that mediates all access",
"requirements": [
"Complete mediation",
"Isolation from subjects",
"Verification possible"
],
"implementation": "Security kernel or hypervisor"
},
"security_levels": {
"user_mode": "Unprivileged execution mode",
"kernel_mode": "Privileged execution mode",
"hypervisor_mode": "Higher privilege than kernel",
"hardware_mode": "Hardware-enforced security"
}
}
Threat Models
Learn to identify and analyze potential threats against operating system security.
Common OS Threats:
• Privilege escalation attacks
• Code injection and execution
• Information disclosure
• Denial of service attacks
• Malware and rootkits
• Physical access attacks
Attack Vectors:
Operating systems face threats from multiple vectors including network attacks, local attacks, physical access, and supply chain compromises. Understanding these helps design appropriate defenses.
# OS Threat Model
os_threat_model = {
"privilege_escalation": {
"description": "Gaining higher privileges than authorized",
"methods": ["Buffer overflows", "Race conditions", "Configuration errors"],
"targets": ["Kernel", "System services", "SUID programs"],
"mitigations": ["DEP/NX", "ASLR", "Control flow integrity"]
},
"malware_threats": {
"types": ["Viruses", "Worms", "Trojans", "Rootkits", "Ransomware"],
"infection_vectors": ["Email", "Downloads", "Removable media", "Network"],
"persistence_methods": ["Registry", "Boot sectors", "System files"],
"defenses": ["Antivirus", "Behavior monitoring", "Application control"]
},
"physical_threats": {