FS寄存器到_TEB线程环境块

FS寄存器到_TEB线程环境块

 

From http://www.cppblog.com/Alexxu/archive/2010/01/20/106066.aspx

从FS寄存器获取当前线程ID
int GetThreadId()
{
 int ithread = 0;
 _asm{
    xor esi , esi
    mov eax, fs:[esi+18h]     
       mov ecx, [eax+ 20h]
       mov eax, [eax+ 24h]
    mov dword ptr[ithread], eax
 }
 return ithread;
}
从FS寄存器获取当前进程ID
int GetProcessId()
{
 int iProcess = 0;
 _asm{
    xor esi , esi
    mov eax, fs:[esi+18h]
       mov ecx, [eax+ 20h]
       mov eax, [eax+ 24h]
    mov dword ptr[iProcess ], ecx
 }
 return iProcess ;
}

原理：
1.fs:18h 地址指向线程环境块_TEB
打开windbg可以证明：
0:028> dd fs:18h L1
0053:00000018  7eeb8000
0:028> !teb
TEB at 7eeb8000
    ExceptionList:        1f8ff15c
    StackBase:            1f900000
    StackLimit:           1f8fc000
    SubSystemTib:         00000000
    FiberData:            00001e00
    ArbitraryUserPointer: 00000000
    Self:                 7eeb8000
    EnvironmentPointer:   00000000
    ClientId:             00001a30 . 00001408
    RpcHandle:            00000000
    Tls Storage:          133d2718
    PEB Address:          7efde000
    LastErrorValue:       0
    LastStatusValue:      c0000302
    Count Owned Locks:    0
    HardErrorMode:        0

2. 在_TEB中找到线程ID和进程ID
0:028> dt ntdll!_TEB
   +0x000 NtTib            : _NT_TIB
   +0x01c EnvironmentPointer : Ptr32 Void
   +0x020 ClientId         : _CLIENT_ID

0:028> dt ntdll!_CLIENT_ID
   +0x000 UniqueProcess    : Ptr32 Void  >进程ID
   +0x004 UniqueThread     : Ptr32 Void  >线程ID

当然从TEB又可以找到_PEB的地址，从_PEB里面可以获取到更多的信息。暂且搁笔~~