kexec-debug.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#include <linux/reboot.h>
#include <sys/reboot.h>
#include <sys/syscall.h>
#include <linux/kexec.h>
#include <sys/types.h>
#include <signal.h>
#include <sys/stat.h>
#include <fcntl.h>

#define KERNEL_BASEURL "https://bootstrap.gig.tech/kernel/"
#define KERNEL_FILE    "zero-os-HEAD-0-core-1cfdbc6ff9.efi"

void diep(char *str) {
    perror(str);
    exit(EXIT_FAILURE);
}

int main(void) {
    int kfd;
    char cmdline[2048];

    printf("[+] downloading kernel\n");
    chdir("/tmp/");
    system("wget " KERNEL_BASEURL KERNEL_FILE);

    printf("[+] reading current kernel cmdline\n");
    if((kfd = open("/proc/cmdline", O_RDONLY)) < 0)
        diep("/proc/cmdline");

    if(read(kfd, cmdline, sizeof(cmdline)) < 0)
        diep("read");

    close(kfd);

    printf("[+] opening new kernel file\n");
    if((kfd = open("/tmp/" KERNEL_FILE, O_RDONLY)) < 0)
        diep("kernel open");

    printf("[+] loading new kernel into memory\n");
    if(syscall(SYS_kexec_file_load, kfd, 0, strlen(cmdline) + 1, cmdline, KEXEC_FILE_NO_INITRAMFS) < 0)
        diep("kexec_file_load");

    // here we should kill SIGTERM -1

    printf("[+] flushing buffers\n");
    sync();

    printf("[+] booting the new kernel\n");
    reboot(LINUX_REBOOT_CMD_KEXEC);

    // never reached anyway
    return 0;
}