程序集执行 /bin/bash (x64)

Question

我是 asm 的新手，我正在尝试对 /bin/bash 执行系统调用。但是我目前遇到以下问题：

我的代码适用于第一个参数长度小于 8 个字节的任何 execve 调用，即 "/bin/sh" 或 "/bin/ls" ：

.section .data

    name: .string "/bin/sh"

.section .text

.globl _start

_start:
    #third argument of execve, set to NULL
    xor %rdx, %rdx 

    #push nullbyte to the stack
    pushq %rdx 

    #push /bin/sh to the stack
    pushq name 

    #copy stack to rdi, 1st arg of execve
    mov %rsp, %rdi 

    #copy 59 to rax, defining syscall number for execve  
    movq $59, %rax 

    #3rd arg of execve set to NULL
    movq $0, %rsi 

    syscall

令我困惑的是我无法使用它

name: .string "/bin/bash"

我试图将字符串分成几部分，将“/ bash”然后“/ bin”pushq到堆栈，似乎没有任何东西可以让它工作，并且每次我都会收到“非法指令”错误。我究竟做错了什么？

非工作代码：

.section .data

    name: .string "/bin/bash"

.section .text

.globl _start

_start:
    #third argument of execve, set to NULL
    xor %rdx, %rdx 

    #push nullbyte to the stack
    pushq %rdx 

    #push /bin/sh to the stack
    pushq name 

    #copy stack to rdi, 1st arg of execve
    mov %rsp, %rdi 

    #copy 59 to rax, defining syscall number for execve  
    movq $59, %rax 

    #3rd arg of execve set to NULL
    movq $0, %rsi 

    syscall

其他非工作代码：

.section .data

.section .text

.globl _start

_start:
    #third argument of execve, set to NULL
    xor %rdx, %rdx 

    #push nullbyte to the stack
    pushq %rdx 

    #push /bin/bash to the stack
    pushq $0x68
    pushq $0x7361622f
    pushq $0x6e69622f

    #copy stack to rdi, 1st arg of execve
    mov %rsp, %rdi 

    #copy 59 to rax, defining syscall number for execve  
    movq $59, %rax 

    #3rd arg of execve set to NULL
    movq $0, %rsi 

    syscall

Answer 1

您似乎完全糊涂了，无法列出所有错误。不过，这里有一份不完整的清单：

1. 您将 esi 设置为零的含义argv是NULL
2. push nullbyte to the stack实际上是一个NULL用于终止argv数组的指针（它不是一个终止字符串的零字节）。
3. 您需要将文件名的地址作为argv[0]. 您不需要将字符串复制到堆栈中。

这是一个固定版本：

.section .data

    name: .string "/bin/bash"

.section .text

.globl _start

_start:
    # third argument of execve is envp, set to NULL
    xor %rdx, %rdx 

    # push NULL to the stack, argv terminator
    pushq %rdx 

    # first argument to execve is the file name
    leaq name, %rdi

    # also argv[0]
    push %rdi

    # second argument to execve is argv
    mov %rsp, %rsi

    #copy 59 to rax, defining syscall number for execve  
    movq $59, %rax 
    syscall

还有一个从代码在堆栈上创建字符串的版本，没有零字节：

.section .text

.globl _start

_start:
    # third argument of execve is envp, set to NULL
    xor %rdx, %rdx 

    # zero terminator
    push %rdx

    # space for string
    sub $16, %rsp

    # end is aligned to the zero terminator
    movb $0x2f, 7(%rsp)        # /
    movl $0x2f6e6962, 8(%rsp)  # bin/
    movl $0x68736162, 12(%rsp) # bash

    # first argument to execve is the file name
    leaq 7(%rsp), %rdi

    # push NULL to the stack, argv terminator
    pushq %rdx 

    # also argv[0]
    push %rdi

    # second argument to execve is argv
    mov %rsp, %rsi

    # copy 59 to rax, defining syscall number for execve
    # avoid zero byte
    xor %eax, %eax
    movb $59, %al 
    syscall