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007——逆向之OC反汇编

007——逆向之OC反汇编

作者: 为自己丶拼个未来 | 来源:发表于2018-05-22 16:12 被阅读0次

block反汇编

  • 全局静态block
int main(int argc, char * argv[]) {
    void (^block)(void) = ^(){
        NSLog(@"block");
    };

    block();
}

反汇编的代码如下:


block的汇编代码

当看到
0x100c121e8 <+12>: adrp x8, 10
0x100c121ec <+16>: add x8, x8, #0x428
说明附近有个isa的block指针

  • 访问外部变量的block
int main(int argc, char * argv[]) {
    int a = 10;
    void (^block)(void) = ^(){
        NSLog(@"block---%d", a);
    };

    block();
}
外部变量的block

OC方法反汇编

@interface Person : NSObject

@property (nonatomic, copy) NSString *name;
@property (nonatomic, assign) NSInteger age;

@end

int main(int argc, char * argv[]) {

    Person *p = [[Person alloc] init];

}
OC方法反汇编
/*
 所有OC中使用Strong 修饰的对象,实际上是调用了这个函数 objc_storeStrong
 void objc_storeStrong(id *location,id obj)
 {
    id perv = *lopcation;
    if(obj == prev){
        return;
    }
    objc_retain(obj);
    *location = obj;
    objc_release(prev);
 }
 */

OC对象如何释放的呢?

OC对象释放

很明显最后的x1寄存器给了0x0000000000000000,也就是内存释放了即p=nil。

ASLR

aslr是一种针对缓冲区溢出的安全保护技术,通过对堆、栈、共享库映射等线性区布局的随机化,通过增加攻击者预测目的地址的难度,防止攻击者直接定位攻击代码位置,达到阻止溢出攻击的目的的一种技术。

ASLR(Address space layout randomization)是一种针对缓冲区溢出的安全保护技术,通过对堆、栈、共享库映射等线性区布局的随机化,通过增加攻击者预测目的地址的难度,防止攻击者直接定位攻击代码位置,达到阻止溢出攻击的目的。据研究表明ASLR可以有效的降低缓冲区溢出攻击的成功率,如今Linux、FreeBSD、Windows等主流操作系统都已采用了该技术。

Mac OS X

Apple在Mac OS X Leopard10.5(2007年十月发行)中某些库导入了随机地址偏移,但其实现并没有提供ASLR所定义的完整保护能力。而Mac OS X Lion10.7则对所有的应用程序均提供了ASLR支持。Apple宣称为应用程序改善了这项技术的支持,能让32及64位的应用程序避开更多此类攻击。从OS X Mountain Lion10.8开始,核心及核心扩充(kext)与zones在系统启动时也会随机配置。

iOS(iPhone, iPod touch, iPad)
Apple在iOS4.3内导入了ASLR。


image.png ASLR.png

cmp(Compare)比较指令

CMP 把一个寄存器的内容和另一个寄存器的内容或立即数进行比较。但不存储结果,只是正确的更改标志。
   一般CMP做完判断后会进行跳转,后面通常会跟上B指令!

BL 标号:跳转到标号处执行
B.GT 标号:比较结果是大于(greater than),执行标号,否则不跳转
B.GE 标号:比较结果是大于等于(greater than or equal to),执行标号,否则不跳转
B.EQ 标号:比较结果是等于,执行标号,否则不跳转
B.HI 标号:比较结果是无符号大于,执行标号,否则不跳转


Switch

  • 假设switch语句的分支比较少的时候(例如3,少于4的时候没有意义)没有必要使用此结构,相当于if。
__text:00000001000067F8                 EXPORT _funA
__text:00000001000067F8 _funA                                   ; CODE XREF: _main+20↓p
__text:00000001000067F8
__text:00000001000067F8 var_24          = -0x24
__text:00000001000067F8 var_20          = -0x20
__text:00000001000067F8 var_1C          = -0x1C
__text:00000001000067F8 var_18          = -0x18
__text:00000001000067F8 var_14          = -0x14
__text:00000001000067F8 var_10          = -0x10
__text:00000001000067F8 var_C           = -0xC
__text:00000001000067F8 var_8           = -8
__text:00000001000067F8 var_4           = -4
__text:00000001000067F8 var_s0          =  0
__text:00000001000067F8
__text:00000001000067F8                 SUB             SP, SP, #0x40
__text:00000001000067FC                 STP             X29, X30, [SP,#0x30+var_s0]
__text:0000000100006800                 ADD             X29, SP, #0x30
__text:0000000100006804                 STUR            W0, [X29,#var_4]
__text:0000000100006808                 LDUR            W0, [X29,#var_4]
__text:000000010000680C                 MOV             X8, X0
__text:0000000100006810                 SUBS            W0, W0, #1
__text:0000000100006814                 STUR            W8, [X29,#var_8]
__text:0000000100006818                 STUR            W0, [X29,#var_C]
__text:000000010000681C                 B.EQ            loc_10000684C
__text:0000000100006820                 B               loc_100006824
__text:0000000100006824 ; ---------------------------------------------------------------------------
__text:0000000100006824
__text:0000000100006824 loc_100006824                           ; CODE XREF: _funA+28↑j
__text:0000000100006824                 LDUR            W8, [X29,#var_8]
__text:0000000100006828                 SUBS            W9, W8, #2
__text:000000010000682C                 STUR            W9, [X29,#var_10]
__text:0000000100006830                 B.EQ            loc_100006860
__text:0000000100006834                 B               loc_100006838
__text:0000000100006838 ; ---------------------------------------------------------------------------
__text:0000000100006838
__text:0000000100006838 loc_100006838                           ; CODE XREF: _funA+3C↑j
__text:0000000100006838                 LDUR            W8, [X29,#var_8]
__text:000000010000683C                 SUBS            W9, W8, #3
__text:0000000100006840                 STUR            W9, [X29,#var_14]
__text:0000000100006844                 B.EQ            loc_100006874
__text:0000000100006848                 B               loc_100006888
__text:000000010000684C ; ---------------------------------------------------------------------------
__text:000000010000684C
__text:000000010000684C loc_10000684C                           ; CODE XREF: _funA+24↑j
__text:000000010000684C                 ADRP            X0, #asc_100007F08@PAGE ; "打坐"
__text:0000000100006850                 ADD             X0, X0, #asc_100007F08@PAGEOFF ; "打坐"
__text:0000000100006854                 BL              _printf
__text:0000000100006858                 STR             W0, [SP,#0x30+var_18]
__text:000000010000685C                 B               loc_100006898
__text:0000000100006860 ; ---------------------------------------------------------------------------
__text:0000000100006860
__text:0000000100006860 loc_100006860                           ; CODE XREF: _funA+38↑j
__text:0000000100006860                 ADRP            X0, #asc_100007F0F@PAGE ; "加红"
__text:0000000100006864                 ADD             X0, X0, #asc_100007F0F@PAGEOFF ; "加红"
__text:0000000100006868                 BL              _printf
__text:000000010000686C                 STR             W0, [SP,#0x30+var_1C]
__text:0000000100006870                 B               loc_100006898
__text:0000000100006874 ; ---------------------------------------------------------------------------
__text:0000000100006874
__text:0000000100006874 loc_100006874                           ; CODE XREF: _funA+4C↑j
__text:0000000100006874                 ADRP            X0, #asc_100007F16@PAGE ; "加蓝"
__text:0000000100006878                 ADD             X0, X0, #asc_100007F16@PAGEOFF ; "加蓝"
__text:000000010000687C                 BL              _printf
__text:0000000100006880                 STR             W0, [SP,#0x30+var_20]
__text:0000000100006884                 B               loc_100006898
__text:0000000100006888 ; ---------------------------------------------------------------------------
__text:0000000100006888
__text:0000000100006888 loc_100006888                           ; CODE XREF: _funA+50↑j
__text:0000000100006888                 ADRP            X0, #asc_100007F1D@PAGE ; "啥都不干"
__text:000000010000688C                 ADD             X0, X0, #asc_100007F1D@PAGEOFF ; "啥都不干"
__text:0000000100006890                 BL              _printf
__text:0000000100006894                 STR             W0, [SP,#0x30+var_24]
__text:0000000100006898
__text:0000000100006898 loc_100006898                           ; CODE XREF: _funA+64↑j
__text:0000000100006898                                         ; _funA+78↑j ...
__text:0000000100006898                 LDP             X29, X30, [SP,#0x30+var_s0]
__text:000000010000689C                 ADD             SP, SP, #0x40
__text:00000001000068A0                 RET
__text:00000001000068A0 ; End of function _funA
  • 各个分支常量的差值较大的时候,编译器会在效率还是内存进行取舍,这个时候编译器还是会编译成类似于if,else的结构。
__text:00000001000067C8                 EXPORT _funA
__text:00000001000067C8 _funA                                   ; CODE XREF: _main+20↓p
__text:00000001000067C8
__text:00000001000067C8 var_2C          = -0x2C
__text:00000001000067C8 var_28          = -0x28
__text:00000001000067C8 var_24          = -0x24
__text:00000001000067C8 var_20          = -0x20
__text:00000001000067C8 var_1C          = -0x1C
__text:00000001000067C8 var_18          = -0x18
__text:00000001000067C8 var_14          = -0x14
__text:00000001000067C8 var_10          = -0x10
__text:00000001000067C8 var_C           = -0xC
__text:00000001000067C8 var_8           = -8
__text:00000001000067C8 var_4           = -4
__text:00000001000067C8 var_s0          =  0
__text:00000001000067C8
__text:00000001000067C8                 SUB             SP, SP, #0x40
__text:00000001000067CC                 STP             X29, X30, [SP,#0x30+var_s0]
__text:00000001000067D0                 ADD             X29, SP, #0x30
__text:00000001000067D4                 STUR            W0, [X29,#var_4]
__text:00000001000067D8                 LDUR            W0, [X29,#var_4]
__text:00000001000067DC                 MOV             X8, X0
__text:00000001000067E0                 SUBS            W0, W0, #1
__text:00000001000067E4                 STUR            W8, [X29,#var_8]
__text:00000001000067E8                 STUR            W0, [X29,#var_C]
__text:00000001000067EC                 B.EQ            loc_100006830
__text:00000001000067F0                 B               loc_1000067F4
__text:00000001000067F4 ; ---------------------------------------------------------------------------
__text:00000001000067F4
__text:00000001000067F4 loc_1000067F4                           ; CODE XREF: _funA+28↑j
__text:00000001000067F4                 LDUR            W8, [X29,#var_8]
__text:00000001000067F8                 SUBS            W9, W8, #4
__text:00000001000067FC                 STUR            W9, [X29,#var_10]
__text:0000000100006800                 B.EQ            loc_10000686C
__text:0000000100006804                 B               loc_100006808
__text:0000000100006808 ; ---------------------------------------------------------------------------
__text:0000000100006808
__text:0000000100006808 loc_100006808                           ; CODE XREF: _funA+3C↑j
__text:0000000100006808                 LDUR            W8, [X29,#var_8]
__text:000000010000680C                 SUBS            W9, W8, #0xC8
__text:0000000100006810                 STUR            W9, [X29,#var_14]
__text:0000000100006814                 B.EQ            loc_100006844
__text:0000000100006818                 B               loc_10000681C
__text:000000010000681C ; ---------------------------------------------------------------------------
__text:000000010000681C
__text:000000010000681C loc_10000681C                           ; CODE XREF: _funA+50↑j
__text:000000010000681C                 LDUR            W8, [X29,#var_8]
__text:0000000100006820                 SUBS            W9, W8, #0x1F4
__text:0000000100006824                 STR             W9, [SP,#0x30+var_18]
__text:0000000100006828                 B.EQ            loc_100006858
__text:000000010000682C                 B               loc_100006880
__text:0000000100006830 ; ---------------------------------------------------------------------------
__text:0000000100006830
__text:0000000100006830 loc_100006830                           ; CODE XREF: _funA+24↑j
__text:0000000100006830                 ADRP            X0, #asc_100007F00@PAGE ; "打坐"
__text:0000000100006834                 ADD             X0, X0, #asc_100007F00@PAGEOFF ; "打坐"
__text:0000000100006838                 BL              _printf
__text:000000010000683C                 STR             W0, [SP,#0x30+var_1C]
__text:0000000100006840                 B               loc_100006890
__text:0000000100006844 ; ---------------------------------------------------------------------------
__text:0000000100006844
__text:0000000100006844 loc_100006844                           ; CODE XREF: _funA+4C↑j
__text:0000000100006844                 ADRP            X0, #asc_100007F07@PAGE ; "加红"
__text:0000000100006848                 ADD             X0, X0, #asc_100007F07@PAGEOFF ; "加红"
__text:000000010000684C                 BL              _printf
__text:0000000100006850                 STR             W0, [SP,#0x30+var_20]
__text:0000000100006854                 B               loc_100006890
__text:0000000100006858 ; ---------------------------------------------------------------------------
__text:0000000100006858
__text:0000000100006858 loc_100006858                           ; CODE XREF: _funA+60↑j
__text:0000000100006858                 ADRP            X0, #asc_100007F0E@PAGE ; "加蓝"
__text:000000010000685C                 ADD             X0, X0, #asc_100007F0E@PAGEOFF ; "加蓝"
__text:0000000100006860                 BL              _printf
__text:0000000100006864                 STR             W0, [SP,#0x30+var_24]
__text:0000000100006868                 B               loc_100006890
__text:000000010000686C ; ---------------------------------------------------------------------------
__text:000000010000686C
__text:000000010000686C loc_10000686C                           ; CODE XREF: _funA+38↑j
__text:000000010000686C                 ADRP            X0, #asc_100007F15@PAGE ; "摆摊"
__text:0000000100006870                 ADD             X0, X0, #asc_100007F15@PAGEOFF ; "摆摊"
__text:0000000100006874                 BL              _printf
__text:0000000100006878                 STR             W0, [SP,#0x30+var_28]
__text:000000010000687C                 B               loc_100006890
__text:0000000100006880 ; ---------------------------------------------------------------------------
__text:0000000100006880
__text:0000000100006880 loc_100006880                           ; CODE XREF: _funA+64↑j
__text:0000000100006880                 ADRP            X0, #asc_100007F1C@PAGE ; "啥都不干"
__text:0000000100006884                 ADD             X0, X0, #asc_100007F1C@PAGEOFF ; "啥都不干"
__text:0000000100006888                 BL              _printf
__text:000000010000688C                 STR             W0, [SP,#0x30+var_2C]
__text:0000000100006890
__text:0000000100006890 loc_100006890                           ; CODE XREF: _funA+78↑j
__text:0000000100006890                                         ; _funA+8C↑j ...
__text:0000000100006890                 LDP             X29, X30, [SP,#0x30+var_s0]
__text:0000000100006894                 ADD             SP, SP, #0x40
__text:0000000100006898                 RET
__text:0000000100006898 ; End of function _funA
  • 在分支比较多的时候:在编译的时候会生成一个表(跳转表每个地址四个字节)
__text:00000001000067DC                 EXPORT _funA
__text:00000001000067DC _funA                                   ; CODE XREF: _main+20↓p
__text:00000001000067DC
__text:00000001000067DC var_28          = -0x28
__text:00000001000067DC var_24          = -0x24
__text:00000001000067DC var_20          = -0x20
__text:00000001000067DC var_1C          = -0x1C
__text:00000001000067DC var_18          = -0x18
__text:00000001000067DC var_14          = -0x14
__text:00000001000067DC var_10          = -0x10
__text:00000001000067DC var_4           = -4
__text:00000001000067DC var_s0          =  0
__text:00000001000067DC
__text:00000001000067DC                 SUB             SP, SP, #0x40
__text:00000001000067E0                 STP             X29, X30, [SP,#0x30+var_s0]
__text:00000001000067E4                 ADD             X29, SP, #0x30
__text:00000001000067E8                 STUR            W0, [X29,#var_4]
__text:00000001000067EC                 LDUR            W0, [X29,#var_4]
__text:00000001000067F0                 SUBS            W0, W0, #1 ; switch 4 cases
__text:00000001000067F4                 MOV             X8, X0
__text:00000001000067F8                 SUBS            W0, W0, #3
__text:00000001000067FC                 STUR            X8, [X29,#var_10]
__text:0000000100006800                 STUR            W0, [X29,#var_14]
__text:0000000100006804                 B.HI            def_10000681C ; jumptable 000000010000681C default case
__text:0000000100006808                 ADRP            X8, #jpt_10000681C@PAGE
__text:000000010000680C                 ADD             X8, X8, #jpt_10000681C@PAGEOFF
__text:0000000100006810                 LDUR            X9, [X29,#var_10]
__text:0000000100006814                 LDRSW           X10, [X8,X9,LSL#2]
__text:0000000100006818                 ADD             X8, X10, X8
__text:000000010000681C                 BR              X8      ; switch jump
__text:0000000100006820 ; ---------------------------------------------------------------------------
__text:0000000100006820
__text:0000000100006820 loc_100006820                           ; CODE XREF: _funA+40↑j
__text:0000000100006820                                         ; DATA XREF: __text:jpt_10000681C↓o
__text:0000000100006820                 ADRP            X0, #asc_100007F00@PAGE ; jumptable 000000010000681C case 1
__text:0000000100006824                 ADD             X0, X0, #asc_100007F00@PAGEOFF ; "打坐"
__text:0000000100006828                 BL              _printf
__text:000000010000682C                 STR             W0, [SP,#0x30+var_18]
__text:0000000100006830                 B               loc_100006880
__text:0000000100006834 ; ---------------------------------------------------------------------------
__text:0000000100006834
__text:0000000100006834 loc_100006834                           ; CODE XREF: _funA+40↑j
__text:0000000100006834                                         ; DATA XREF: __text:0000000100006890↓o
__text:0000000100006834                 ADRP            X0, #asc_100007F07@PAGE ; jumptable 000000010000681C case 2
__text:0000000100006838                 ADD             X0, X0, #asc_100007F07@PAGEOFF ; "加红"
__text:000000010000683C                 BL              _printf
__text:0000000100006840                 STR             W0, [SP,#0x30+var_1C]
__text:0000000100006844                 B               loc_100006880
__text:0000000100006848 ; ---------------------------------------------------------------------------
__text:0000000100006848
__text:0000000100006848 loc_100006848                           ; CODE XREF: _funA+40↑j
__text:0000000100006848                                         ; DATA XREF: __text:0000000100006894↓o
__text:0000000100006848                 ADRP            X0, #asc_100007F0E@PAGE ; jumptable 000000010000681C case 3
__text:000000010000684C                 ADD             X0, X0, #asc_100007F0E@PAGEOFF ; "加蓝"
__text:0000000100006850                 BL              _printf
__text:0000000100006854                 STR             W0, [SP,#0x30+var_20]
__text:0000000100006858                 B               loc_100006880
__text:000000010000685C ; ---------------------------------------------------------------------------
__text:000000010000685C
__text:000000010000685C loc_10000685C                           ; CODE XREF: _funA+40↑j
__text:000000010000685C                                         ; DATA XREF: __text:0000000100006898↓o
__text:000000010000685C                 ADRP            X0, #asc_100007F15@PAGE ; jumptable 000000010000681C case 4
__text:0000000100006860                 ADD             X0, X0, #asc_100007F15@PAGEOFF ; "摆摊"
__text:0000000100006864                 BL              _printf
__text:0000000100006868                 STR             W0, [SP,#0x30+var_24]
__text:000000010000686C                 B               loc_100006880
__text:0000000100006870 ; ---------------------------------------------------------------------------
__text:0000000100006870
__text:0000000100006870 def_10000681C                           ; CODE XREF: _funA+28↑j
__text:0000000100006870                 ADRP            X0, #asc_100007F1C@PAGE ; jumptable 000000010000681C default case
__text:0000000100006874                 ADD             X0, X0, #asc_100007F1C@PAGEOFF ; "啥都不干"
__text:0000000100006878                 BL              _printf
__text:000000010000687C                 STR             W0, [SP,#0x30+var_28]
__text:0000000100006880
__text:0000000100006880 loc_100006880                           ; CODE XREF: _funA+54↑j
__text:0000000100006880                                         ; _funA+68↑j ...
__text:0000000100006880                 LDP             X29, X30, [SP,#0x30+var_s0]
__text:0000000100006884                 ADD             SP, SP, #0x40
__text:0000000100006888                 RET
__text:0000000100006888 ; End of function _funA

还原高级代码(if...else...)

OC代码

#import <UIKit/UIKit.h>
#import "AppDelegate.h"

int g = 12;
void func(int a, int b) {
    if (a > b) {
        g = a;
    } else {
        g = b;
    }
}

int main(int argc, char * argv[]) {
    func(1, 2);
    return 0;
}

main函数汇编分析

__text:00000001000068CC _main
__text:00000001000068CC
__text:00000001000068CC var_10          = -0x10
__text:00000001000068CC var_8           = -8
__text:00000001000068CC var_4           = -4
__text:00000001000068CC var_s0          =  0
__text:00000001000068CC
__text:00000001000068CC                 SUB             SP, SP, #0x20
__text:00000001000068D0                 STP             X29, X30, [SP,#0x10+var_s0]
__text:00000001000068D4                 ADD             X29, SP, #0x10
__text:00000001000068D8                 MOV             W8, #1
int W8 = 1;
__text:00000001000068DC                 MOV             W9, #2
int W9 = 2;
__text:00000001000068E0                 STUR            WZR, [X29,#var_4]
__text:00000001000068E4                 STR             W0, [SP,#0x10+var_8]
int var_8 = W0;
__text:00000001000068E8                 STR             X1, [SP,#0x10+var_10]
int var_10 = X1;
__text:00000001000068EC                 MOV             X0, X8
int X0 = X8;
__text:00000001000068F0                 MOV             X1, X9
int X1 = X9;
__text:00000001000068F4                 BL              _func
跳转到func函数
__text:00000001000068F8                 MOV             W8, #0
__text:00000001000068FC                 MOV             X0, X8
__text:0000000100006900                 LDP             X29, X30, [SP,#0x10+var_s0]
__text:0000000100006904                 ADD             SP, SP, #0x20
__text:0000000100006908                 RET
__text:0000000100006908 ; End of function _main

由此分析:函数名为func,并且带两个参数,参数类型为int。

func函数汇编分析

//__text:0000000100006884                 EXPORT _func
//__text:0000000100006884 _func                                   ; CODE XREF: _main+28↓p
//__text:0000000100006884
//__text:0000000100006884 var_8           = -8
//__text:0000000100006884 var_4           = -4
//__text:0000000100006884
//__text:0000000100006884                 SUB             SP, SP, #0x10
int g = 12;//具体的值需要动态调试得到
void func(int a, int b) {

//__text:0000000100006888                 STR             W0, [SP,#0x10+var_4]
    int var_4 = a;
//__text:000000010000688C                 STR             W1, [SP,#0x10+var_8]
    int var_8 = b;
//__text:0000000100006890                 LDR             W0, [SP,#0x10+var_4]
    int W0 = var_4;
//__text:0000000100006894                 LDR             W1, [SP,#0x10+var_8]
    int W1 = var_8;
//__text:0000000100006898                 CMP             W0, W1

    //__text:000000010000689C                 B.LE            loc_1000068B4

    if (W0 > W1) {
        //__text:00000001000068A0                 ADRP            X8, #_g@PAGE
        //__text:00000001000068A4                 ADD             X8, X8, #_g@PAGEOFF
        int* X8 = &g;
        //__text:00000001000068A8                 LDR             W9, [SP,#0x10+var_4]
        int W9 = var_4;
        //__text:00000001000068AC                 STR             W9, [X8]
        * X8 = W9;
    } else {
        //__text:00000001000068B4                 ADRP            X8, #_g@PAGE
        //__text:00000001000068B8                 ADD             X8, X8, #_g@PAGEOFF
        int* X8 = &g;
        //__text:00000001000068BC                 LDR             W9, [SP,#0x10+var_8]
        int W9 = var_8;
        //__text:00000001000068C0                 STR             W9, [X8]
        * X8 = W9;
    }

//__text:00000001000068C4                 ADD             SP, SP, #0x10
//__text:00000001000068C8                 RET
//__text:00000001000068C8 ; End of function _func
}

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