Kernel-Level Ransomware Killswitch: Intercepting vfs_write with eBPF & Go

The Problem with User-Space Detection

When dealing with ransomware, user-space detection relies heavily on heuristics that can be easily bypassed or suspended by rootkits. By dropping our logic directly into the kernel using eBPF (Extended Berkeley Packet Filter), we can observe block I/O and file system operations in real-time, completely invisible to the attacker.

Hooking vfs_write

The core concept relies on intercepting vfs_write calls using an eBPF fentry probe. By calculating the entropy of the buffer being written in a highly optimized C program within the kernel space, we can send alerts to a user-space Go daemon.

SEC("fentry/vfs_write")
int BPF_PROG(vfs_write_enter, struct file *file, const char __user *buf, size_t count, loff_t *pos) {
    // Entropy calculation and filtering logic
    return 0;
}

If the entropy exceeds a certain threshold (e.g., indicating encrypted data), the Go application can instantly issue a SIGKILL to the offending process.