[分享]ExtOverlay插件判定是否存在Overlay方法-软件逆向-看雪-安全社区|安全招聘|kanxue.com

[分享]ExtOverlay插件判定是否存在Overlay方法

发表于: 2007-8-9 23:39 6481

[分享]ExtOverlay插件判定是否存在Overlay方法

linxer

2007-8-9 23:39

6481

前几天，写了个判定Overlay的东东，都在瞎闭门造车，今天分析了下PEid的ExtOverlay插件的判定算法，这玩意其实很简单。

分析了下别人的东东，对自己写的东东也更自信了几分:)

bp CreateFileA,F9,Alt + F9返回后，到0x0121391F处

0121391A E8 6DFEFFFF    call 0121378C                      ; jmp 到 kernel32.CreateFileA
0121391F A3 7C562101    mov    dword ptr [121567C], eax //保存文件句柄
01213924 833D 7C562101 F>cmp    dword ptr [121567C], -1
0121392B 0F84 30020000 je    01213B61
01213931 6A 00          push 0
01213933 A1 7C562101    mov    eax, dword ptr [121567C]
01213938 50             push eax
01213939 E8 5EFEFFFF    call 0121379C                      ; jmp 到 kernel32.GetFileSize
0121393E A3 84562101    mov    dword ptr [1215684], eax //保存文件大小
01213943 A1 84562101    mov    eax, dword ptr [1215684]
01213948 E8 FBEAFFFF    call 01212448
0121394D A3 80562101    mov    dword ptr [1215680], eax //保存文件缓冲指针
01213952 33C0          xor    eax, eax
01213954 55             push ebp
01213955 68 5A3B2101    push 01213B5A
0121395A 64:FF30       push dword ptr fs:[eax]
0121395D 64:8920       mov    dword ptr fs:[eax], esp
01213960 6A 00          push 0
01213962 8D45 F8       lea    eax, dword ptr [ebp-8]
01213965 50             push eax
01213966 A1 84562101    mov    eax, dword ptr [1215684]
0121396B 50             push eax
0121396C A1 80562101    mov    eax, dword ptr [1215680]
01213971 50             push eax
01213972 A1 7C562101    mov    eax, dword ptr [121567C]
01213977 50             push eax
01213978 E8 27FEFFFF    call 012137A4                      ; jmp 到 kernel32.ReadFile
0121397D E8 CEFEFFFF    call 01213850

01213850 53             push ebx
01213851 56             push esi
01213852 57             push edi
01213853 33C0          xor    eax, eax
01213855 A3 70562101    mov    dword ptr [1215670], eax //[1215670]用来保存Overlay起始地址
0121385A 33C0          xor    eax, eax
0121385C A3 74562101    mov    dword ptr [1215674], eax //[1215674]用来保存Overlay长度
01213861 33F6          xor    esi, esi
01213863 A1 80562101    mov    eax, dword ptr [1215680] //ReadFile读出内容放在
01213868 8B40 3C       mov    eax, dword ptr [eax+3C]
0121386B 0305 80562101 add    eax, dword ptr [1215680]
01213871 8D58 18       lea    ebx, dword ptr [eax+18]
01213874 0FB750 14    movzx edx, word ptr [eax+14] //SizeOfOptionHeader
01213878 03DA          add    ebx, edx //ebx指向节表位置
0121387A 0FB778 06    movzx edi, word ptr [eax+6] //NumberOfSections
0121387E 4F             dec    edi
0121387F 85FF          test edi, edi
01213881 7C 1F          jl    short 012138A2
01213883 47             inc    edi
01213884 BA 00020000    mov    edx, 200
01213889 8B43 10       mov    eax, dword ptr [ebx+10] //SizeOfRawData
0121388C E8 ABFFFFFF    call 0121383C //这个函数作用：SizeOfRawData按0x200向上取整
01213891 8B53 14       mov    edx, dword ptr [ebx+14] //PointerToRawData
01213894 03D0          add    edx, eax
01213896 3BF2          cmp    esi, edx
01213898 73 02          jnb    short 0121389C
0121389A 8BF2          mov    esi, edx //上面三行代码：把SizeOfRawData + PointerToRawData最大值放esi,其中SizeOfRawData为0x200向上取整值，PointerToRawData未按0x200向下作对齐处理
0121389C 83C3 28       add    ebx, 28 //指向下个节
0121389F 4F             dec    edi //节计数减1
012138A0  ^ 75 E2          jnz    short 01213884
012138A2 85F6          test esi, esi
012138A4 76 20          jbe    short 012138C6
012138A6 3B35 84562101 cmp    esi, dword ptr [1215684] //esi与文件大小比较(esi为PE文件有效大小，不含Overlay大小)
012138AC 73 18          jnb    short 012138C6
012138AE A1 80562101    mov    eax, dword ptr [1215680] //esi小于文件大小情况(有Overlay)
012138B3 03C6          add    eax, esi
012138B5 A3 70562101    mov    dword ptr [1215670], eax //保存Overlay起始地址到[1215670]
012138BA A1 84562101    mov    eax, dword ptr [1215684]
012138BF 2BC6          sub    eax, esi
012138C1 A3 74562101    mov    dword ptr [1215674], eax //保存Overlay长度到[1215674]
012138C6 5F             pop    edi
012138C7 5E             pop    esi
012138C8 5B             pop    ebx
012138C9 C3             retn //返回到下面语句

01213982 833D 70562101 0>cmp    dword ptr [1215670], 0
01213989 0F84 7E010000 je    01213B0D //没有发现Overlay则跳
0121398F 8D45 FC       lea    eax, dword ptr [ebp-4] //底下代码大致是再作善后处理了，保存Overlay到文件...
01213992 8B15 B0402101 mov    edx, dword ptr [12140B0]
01213998 E8 B7F6FFFF    call 01213054
0121399D EB 13          jmp    short 012139B2
0121399F 8B45 FC       mov    eax, dword ptr [ebp-4]
012139A2 E8 7DF7FFFF    call 01213124
012139A7 8BD0          mov    edx, eax
012139A9 4A             dec    edx
012139AA 8D45 FC       lea    eax, dword ptr [ebp-4]
012139AD E8 DEF8FFFF    call 01213290
012139B2 8B45 FC       mov    eax, dword ptr [ebp-4]
012139B5 E8 6AF7FFFF    call 01213124
012139BA 8B55 FC       mov    edx, dword ptr [ebp-4]
012139BD 807C02 FF 2E cmp    byte ptr [edx+eax-1], 2E
012139C2  ^ 75 DB          jnz    short 0121399F
012139C4 8D45 FC       lea    eax, dword ptr [ebp-4]
012139C7 BA 903B2101    mov    edx, 01213B90                   ; ovr
012139CC E8 5BF7FFFF    call 0121312C
012139D1 8B45 FC       mov    eax, dword ptr [ebp-4]
012139D4 E8 23F8FFFF    call 012131FC
012139D9 8BD8          mov    ebx, eax

下面给出ExtOverlay的Overlay判定C代码(不容错处理)：

int has_overlay(char * pBuf, int nBufLen)
{
IMAGE_DOS_HEADER * pIDH = (IMAGE_DOS_HEADER *)pBuf;
IMAGE_NT_HEADERS * pINH = (IMAGE_NT_HEADERS *)(pBuf + pIDH->e_lfanew);

int nSectionNum = pINH->FileHeader.NumberOfSections;

IMAGE_SECTION_HEADER * pISH = (IMAGE_SECTION_HEADER *)((char *)pINH + 0x18 + pINH->FileHeader.SizeOfOptionalHeader);

int nPESize = 0;

for(int nIndex = 0; nIndex < nSectionNum; nIndex++, pISH++)
{
int nTemp = ((pISH->SizeOfRawData + 0x200 - 1) / 0x200) * 0x200;
nTemp += pISH->PointerToRawData;

if(nTemp > nPESize)
{
nPESize = nTemp;
}
}

if(nBufLen > nPESize)
{
//pBuf + nPESize是Overlay开始地址
//nBufLen - nPESize是Overlay长度
return 1; //有Overlay
}
else
{
return 0;
}
}