Adjust SELinux Mode
The most direct way to balance security and performance is by adjusting the SELinux mode. The three modes—Enforcing (strictly enforces policies, may impact performance), Permissive (logs violations without blocking, minimal performance overhead), and Disabled (turns off SELinux entirely)—determine how aggressively SELinux enforces access controls. For systems where security is not critical, switching from Enforcing to Permissive can significantly reduce CPU load caused by constant access control checks. This change is made by editing the /etc/selinux/config file (e.g., setting SELINUX=permissive) and rebooting the system. Note that disabling SELinux entirely should only be done if security requirements are minimal, as it eliminates all MAC protections.
Optimize SELinux Policies
Overly complex or redundant policies increase the workload for SELinux’s Access Control Decision (ACD). To streamline policies:
httpd_can_network_connect_db controls whether Apache can access databases). Disabling unnecessary booleans (e.g., setsebool -P httpd_can_network_connect_db off) reduces the number of checks SELinux performs. Use getsebool -a to list all booleans and identify those not needed for your workload.sesearch (e.g., sesearch -a -t httpd_t -c 'file' -p 'read' to check which file read rules are active for the httpd_t context). Remove unused or redundant rules using semodule -X 100 -r unused_module (replace unused_module with the actual module name).targeted), create custom modules for specific applications. For example, write a .te file to define precise rules for a custom app, then compile and install it with checkmodule, semodule_package, and semodule -i. This limits SELinux’s scope to only what’s necessary for the app.Leverage Efficient Context Managers
SELinux uses fastpath modules to provide a low-latency path for trusted processes (e.g., system-critical services). These modules bypass some of the heavier access control checks, reducing CPU overhead. Ensure fastpath is enabled for services that handle high volumes of requests (e.g., web servers, databases). While Ubuntu doesn’t expose fastpath configuration as explicitly as RHEL/CentOS, keeping SELinux in Targeted mode (the default) helps prioritize critical processes, as it limits policy enforcement to specific services rather than the entire system.
Monitor and Analyze Performance
Regularly monitoring SELinux’s impact on system resources helps identify bottlenecks early. Use these tools:
/var/log/audit/audit.log for “AVC denied” messages (e.g., ausearch -m avc -ts recent). These logs show which operations SELinux blocked, helping you pinpoint unnecessary restrictions.perf to profile system calls and flamegraph to visualize performance hotspots. For example, run perf top to see which processes are consuming the most CPU due to SELinux checks.sestatus -v to view current SELinux mode, policy type, and memory usage (e.g., “Policy booleans” section shows active booleans). This gives a quick overview of SELinux’s resource consumption.Regular Maintenance
Keep SELinux and the system up to date to benefit from performance optimizations and security patches. Regularly:
apt (Ubuntu’s package manager) to update SELinux-related packages (e.g., selinux-utils, libselinux1)./var/log/audit/audit.log to prevent it from growing too large (e.g., use auditctl -D to stop logging temporarily, then service rsyslog restart to restart the logging service). Large logs can slow down disk I/O and make analysis harder./etc/selinux/config and custom policy modules (e.g., cp -R /etc/selinux /backup/selinux_backup) before making changes. This ensures you can revert to a working configuration if something goes wrong.
