[Fuzzing] Qiling 框架在 Ubuntu22.04 rootfs下遇到 CPU ISA level 错误的临时解决方案

问题分析

最近在尝试用 Qiling Framework AFLplusplus 进行fuzz，在ubuntu 22.04（GLIBC版本2.35）下构建环境并测试时遇到了以下问题：

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[!]     0x7ffff7dea1cf: syscall ql_syscall_rseq number = 0x14e(334) not implemented
/lib/x86_64-linux-gnu/libc.so.6: CPU ISA level is lower than required
[=]     writev(fd = 0x2, vec = 0x80000000d530, vlen = 0x2) = 0x46
[=]     exit_group(code = 0x7f) = ?

使用动态链接的ELF程序在初始化时会遇到ISA检查错误导致无法启动。最开始按照Qiling的提示，我以为是因为ld.so新引入的rseq系统调用没有被正确实现所导致的，阅读了手册并添加了以下syscall hook后发现并没有效果：

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def null_rseq_impl(ql: Qiling, abi: int, length: int, flags: int, sig: int):
    return 0

ql.os.set_syscall('rseq', null_rseq_impl, QL_INTERCEPT.CALL)

于是翻找ld.so相关检查逻辑的代码，发现该CHECK只是读取了一些常量并进行比较，没有写操作，理论上bypass掉if判断即可：

至于bypass的方式，我想用地址hook来实现，由于Qiling不实现ASLR，ld.so的基地址固定，于是理论上只要找到相关逻辑的jz指令进行hook即可。打开IDA好一通找，由于没有出现字符串的交叉引用，也没有相关函数符号的交叉引用，花了不少时间，最后找到了该逻辑的位置：

实现到Qiling的hook上：

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def bypass_isa_check(ql: Qiling) -> None:
    print("by_pass_isa_check():")
    ql.arch.regs.rip  = 0x15
    pass

ql.hook_address(bypass_isa_check, ld_so_base 0x2389f)

这时程序可以正常运行。

在解决过程中，去官方的 issue 找了一下发现不少人提过同样的问题，目前还没给啥官方解决方案，于是就先用这个暴力方法解决燃眉之急。

完整脚本

Qiling的extensions模块提供了AFL的有关接口，所以完整的用于ubuntu22.04 rootfs的Fuzz脚本如下：

warpper_fuzz.py

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import unicornafl

unicornafl.monkeypatch()

import os
import sys

from typing import Optional

from qiling import *
from qiling.const import QL_VERBOSE, QL_INTERCEPT
from qiling.extensions import pipe
from qiling.extensions import afl

def main(input_file):
    ql = Qiling(
        ["./test"], "/",
        verbose=QL_VERBOSE.OFF)
    
    # set stdin
    ql.os.stdin = pipe.SimpleInStream(sys.stdin.fileno())

    # get address
    base = ql.loader.images[0].base
    call_stk_chk_fail = base   0x1330
    main_addr = base   0x11c9
    
    def by_pass_isa_check(ql: Qiling) -> None:
        print("by_pass_isa_check():")
        ql.arch.regs.rip  = 0x15
        pass
        
    ld_so_base = 0x7ffff7dd5000
    ql.hook_address(by_pass_isa_check, ld_so_base 0x2389f)
    
    def null_rseq_impl(ql: Qiling, abi: int, length: int, flags: int, sig: int):
        return 0

    ql.os.set_syscall('rseq', null_rseq_impl, QL_INTERCEPT.CALL)
    
    def place_input_callback(ql: Qiling, input: bytes, persistent_round: int) -> Optional[bool]:
        # feed fuzzed input to our mock stdin
        ql.os.stdin.write(input)
        # signal afl to proceed with this input
        return True

    def start_afl(ql: Qiling):
        # Have Unicorn fork and start instrumentation.
        afl.ql_afl_fuzz(ql, input_file=input_file, place_input_callback=place_input_callback, exits=[ql.os.exit_point])

    # make the process crash whenever __stack_chk_fail@plt is about to be called.
    # this way afl will count stack protection violations as crashes
    ql.hook_address(callback=lambda x: os.abort(), address=call_stk_chk_fail)
    # set afl instrumentation [re]starting point. we set it to 'main'
    ql.hook_address(callback=start_afl, address=main_addr)
    
    # entry
    ql.run()

if __name__ == "__main__":
    if len(sys.argv) == 1:
        raise ValueError("No input file provided")
    main(sys.argv[1])

fuzz.sh

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#!/bin/bash

afl-fuzz -m none -i input -o output -U python3 ./wrapper_fuzz.py @@

希望能帮到路过的人。

ubuntu glib hook ld sh

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