rdsysno.py

#!/bin/python3

import argparse
import random
import time

def randomize_sysno(sysnos):
    rdsysnos = sysnos[:]
    random.seed(time.time())
    random.shuffle(rdsysnos)

    # Some syscalls are not allowed to be randomized
    # because they are also used by the kernel
    def put_back(syscall):
        i = syscalls.index(syscall)
        j = rdsysnos.index(sysnos[i])
        rdsysnos[i], rdsysnos[j] = rdsysnos[j], rdsysnos[i]

    if "x86_64" in args.input:
        put_back("arch_prctl")
        put_back("restart_syscall")
        put_back("rt_sigreturn")
    
    if "aarch64" in args.input:
        put_back("restart_syscall")
        put_back("rt_sigreturn")

    return rdsysnos

if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="Randomize syscall numbers")
    parser.add_argument("--input", "-i", required=True, help="Input file (syscall.h.in)")
    parser.add_argument("--output", "-o", required=True, help="Output file (syscall.h)")
    parser.add_argument("--table", "-t", required=False, help="Output syscall table (.sysno.tbl)")
    parser.add_argument("--disable", "-d", action="store_true", help="Disable randomization")
    args = parser.parse_args()

    if not ("x86_64" in args.input or "aarch64" in args.input):
        print("Only x86_64 and aarch64 are supported")
        exit(1)

    syscalls, sysnos = [], []
    with open(args.input, "r") as f:
        lines = f.readlines()
        for line in lines:
            arr = line.split()
            if len(arr) < 3:
                continue
            syscalls.append(arr[1].replace("__NR_", ""))
            sysnos.append(int(arr[2]))

    if not args.disable:
        rdsysnos = randomize_sysno(sysnos)
    else:
        rdsysnos = sysnos

    with open(args.output, "w") as f:
        for syscall, sysno in zip(syscalls, rdsysnos):
            f.write(f"#define __NR_{syscall:<35} {sysno}\n")
        f.write("\n")
        for syscall, sysno in zip(syscalls, rdsysnos):
            f.write(f"#define SYS_{syscall:<36} {sysno}\n")
    
    if args.table is not None:
        with open(args.table, "w") as f:
            for sysno, rd in zip(sysnos, rdsysnos):
                f.write(f"{sysno}\n{rd}\n")