eBPF for Advanced Observability and Runtime Security: Programming the Linux Kernel Without Kernel Modules

The Linux kernel has always been a fortress—powerful but largely impenetrable to runtime modifications without deep kernel expertise and dangerous kernel modules. eBPF (extended Berkeley Packet Filter) shatters this paradigm, offering developers a sandboxed gateway to extend kernel functionality safely and efficiently. What started as a packet filtering mechanism has evolved into a revolutionary technology that's reshaping how we approach observability, security monitoring, and network programming in production systems.

The Kernel Programmability Revolution

Traditional kernel development requires writing kernel modules—a process fraught with risks of system crashes, security vulnerabilities, and compatibility nightmares. eBPF changes this equation fundamentally by providing a virtual machine inside the Linux kernel that can execute user-defined programs safely.

At its core, eBPF operates through the bpf() system call, which loads bytecode into the kernel after rigorous verification. The eBPF verifier ensures programs are safe: they can't crash the kernel, access arbitrary memory, or create infinite loops. This verification process makes eBPF programs as safe as user-space applications while running with kernel-level privileges.

The eBPF Architecture

eBPF programs attach to various kernel hooks called attach points:

• Tracepoints: Static instrumentation points in kernel code
• Kprobes/Uprobes: Dynamic instrumentation for kernel/user functions
• System calls: Intercept and monitor syscall entry/exit
• Network hooks: XDP (eXpress Data Path), TC (Traffic Control), socket filters
• Cgroups: Container and process group monitoring

When triggered, eBPF programs can:

• Collect metrics and traces
• Filter or modify network packets
• Make policy decisions for security enforcement
• Trigger user-space notifications via maps

Technical Deep Dive: eBPF in Action

Core Components

eBPF Maps: Shared data structures between kernel and user space, supporting various types:

// Example: Per-CPU array for performance counters
struct {
    __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
    __uint(max_entries, 256);
    __type(key, __u32);
    __type(value, __u64);
} stats_map SEC(".maps");

eBPF Programs: Event-driven functions compiled to eBPF bytecode:

SEC("tracepoint/syscalls/sys_enter_openat")
int trace_openat(struct trace_event_raw_sys_enter* ctx) {
    __u64 *counter;
    __u32 key = 0;
    
    counter = bpf_map_lookup_elem(&stats_map, &key);
    if (counter) {
        __sync_fetch_and_add(counter, 1);
    }
    
    return 0;
}

Real-World Observability Example

Here's a complete eBPF program for monitoring file operations across the system:

#include <linux/bpf.h>
#include <bpf/bpf_helpers.h>
#include <linux/ptrace.h>

struct file_event {
    __u32 pid;
    __u32 uid;
    char filename[256];
    __u64 timestamp;
};

struct {
    __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
    __uint(key_size, sizeof(__u32));
    __uint(value_size, sizeof(__u32));
} events SEC(".maps");

SEC("tracepoint/syscalls/sys_enter_openat")
int trace_file_open(struct trace_event_raw_sys_enter* ctx) {
    struct file_event event = {};
    
    event.pid = bpf_get_current_pid_tgid() >> 32;
    event.uid = bpf_get_current_uid_gid() & 0xFFFFFFFF;
    event.timestamp = bpf_ktime_get_ns();
    
    // Copy filename from user space
    bpf_probe_read_user_str(event.filename, sizeof(event.filename),
                           (void*)ctx->args[1]);
    
    // Send event to user space
    bpf_perf_event_output(ctx, &events, BPF_F_CURRENT_CPU,
                         &event, sizeof(event));
    
    return 0;
}

char LICENSE[] SEC("license") = "GPL";

Production Security Monitoring

eBPF excels at runtime security monitoring without performance overhead. Here's an example detecting suspicious process execution patterns:

SEC("tracepoint/syscalls/sys_enter_execve")
int detect_suspicious_exec(struct trace_event_raw_sys_enter* ctx) {
    char filename[256];
    __u32 pid = bpf_get_current_pid_tgid() >> 32;
    
    bpf_probe_read_user_str(filename, sizeof(filename), 
                           (void*)ctx->args[0]);
    
    // Flag execution of common attack tools
    if (bpf_strstr(filename, "/tmp/") || 
        bpf_strstr(filename, "nc") ||
        bpf_strstr(filename, "ncat") ||
        bpf_strstr(filename, "/dev/shm/")) {
        
        struct security_alert alert = {
            .pid = pid,
            .alert_type = SUSPICIOUS_EXEC,
            .timestamp = bpf_ktime_get_ns()
        };
        
        bpf_strncpy(alert.details, filename, sizeof(alert.details));
        bpf_perf_event_output(ctx, &security_events, BPF_F_CURRENT_CPU,
                             &alert, sizeof(alert));
    }
    
    return 0;
}

Network Programming with XDP

eBPF's XDP (eXpress Data Path) enables packet processing at the earliest possible point in the network stack:

SEC("xdp")
int ddos_protection(struct xdp_md *ctx) {
    void *data_end = (void *)(long)ctx->data_end;
    void *data = (void *)(long)ctx->data;
    struct ethhdr *eth = data;
    struct iphdr *ip;
    
    // Bounds checking
    if ((void *)(eth + 1) > data_end)
        return XDP_ABORTED;
        
    if (eth->h_proto != htons(ETH_P_IP))
        return XDP_PASS;
        
    ip = (void *)(eth + 1);
    if ((void *)(ip + 1) > data_end)
        return XDP_ABORTED;
    
    // Rate limiting logic
    __u32 src_ip = ip->saddr;
    __u64 *packet_count = bpf_map_lookup_elem(&rate_limit_map, &src_ip);
    
    if (packet_count) {
        if (*packet_count > RATE_LIMIT_THRESHOLD) {
            return XDP_DROP;  // Drop packet
        }
        __sync_fetch_and_add(packet_count, 1);
    }
    
    return XDP_PASS;
}

Production Adoption and Tooling Ecosystem

Major tech companies have embraced eBPF for critical infrastructure:

• Netflix: Uses eBPF for container monitoring and network observability across their microservices architecture
• Facebook/Meta: Employs eBPF in their data center load balancing (Katran) and container security systems
• Google: Leverages eBPF for Kubernetes networking through projects like Cilium
• Cloudflare: Utilizes eBPF for DDoS protection and edge computing workloads

Essential eBPF Tools

BCC (BPF Compiler Collection): Python-based framework for rapid eBPF development

from bcc import BPF

# One-liner to trace all file opens
b = BPF(text="""
int trace_open(struct pt_regs *ctx, const char __user *filename) {
    bpf_trace_printk("Opened: %s\\n", filename);
    return 0;
}
""")

b.attach_kprobe(event="do_sys_openat2", fn_name="trace_open")
b.trace_print()

bpftrace: High-level tracing language for ad-hoc analysis

# Monitor all syscalls by process
bpftrace -e 'tracepoint:raw_syscalls:sys_enter { @[comm] = count(); }'

# Track memory allocations
bpftrace -e 'kprobe:__kmalloc { @bytes[comm] = sum(arg0); }'

Cilium: Production-ready eBPF networking and security for Kubernetes Falco: Runtime security monitoring using eBPF for threat detection

Performance and Limitations

eBPF programs operate with near-zero overhead—often less than 1% CPU impact for comprehensive monitoring. The verifier ensures programs complete in bounded time and can't access arbitrary kernel memory.

Key limitations include:

• Maximum 1 million instructions per program
• Limited stack space (512 bytes)
• No unbounded loops or recursion
• Restricted helper function set
• Program complexity constraints

The Future of Kernel Programmability

eBPF represents a fundamental shift toward programmable infrastructure. As the technology matures, we're seeing expansion beyond Linux into Windows (via eBPF for Windows project) and specialized hardware acceleration.

The implications extend far beyond traditional system administration—eBPF enables a new class of applications that blur the line between kernel and user space, offering unprecedented visibility into system behavior while maintaining safety and performance.

For organizations building modern distributed systems, eBPF isn't just a nice-to-have observability tool—it's becoming essential infrastructure for understanding, securing, and optimizing complex production environments. The ability to safely extend kernel functionality without kernel modules opens possibilities we're only beginning to explore.

Key Takeaways

1. Safety First: eBPF's verification system ensures kernel stability while enabling powerful extensions
2. Production Ready: Major companies rely on eBPF for critical infrastructure monitoring and security
3. Performance: Near-zero overhead monitoring and packet processing capabilities
4. Ecosystem: Rich tooling from BCC/bpftrace for development to Cilium/Falco for production
5. Future-Proof: eBPF adoption is accelerating across cloud-native and security domains

The era of black-box kernel operations is ending. eBPF puts unprecedented visibility and control into developers' hands, making the impossible not just possible, but practical for production use.

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Sources:

• eBPF Applications Landscape
• Linux bpf(2) manual page
• eBPF Verifier Documentation
• Netflix eBPF Flow Logs
• BCC GitHub Repository
• eBPF for Windows