fs:[0]到底表示什么？fs段寄存器在WINDOWS系统中的作用

在进行WINDOWS开发的过程中，有一个重要的地址保存着每个程序或者说代码运行的关键信息，它就是fs:[0]地址的所指向的一块数据区，它其实就是用来保存当前进程关键信息的进程控制块数据结构，在内核态环境下，它表示的是进行控制块KPCB结构体，在用户态环境下，它的表示形式是线程控制块的用户态形式TEB，为了容易阅读，这里使用了REACTOS的相关源码来描述：

typedef struct _KPCR
{
    _ANONYMOUS_UNION union
    {
        NT_TIB NtTib;                  //这里是当前线程的控制块
        _ANONYMOUS_STRUCT struct
        {
            union _KGDTENTRY64 *GdtBase;       ///gdt表
            struct _KTSS64 *TssBase;
            ULONG64 UserRsp;
            struct _KPCR *Self;
            struct _KPRCB *CurrentPrcb;
            PKSPIN_LOCK_QUEUE LockArray;
            PVOID Used_Self;
        };
    };
    union _KIDTENTRY64 *IdtBase;
    ULONG64 Unused[2];
    KIRQL Irql;
    UCHAR SecondLevelCacheAssociativity;
    UCHAR ObsoleteNumber;
    UCHAR Fill0;
    ULONG Unused0[3];
    USHORT MajorVersion;
    USHORT MinorVersion;
    ULONG StallScaleFactor;
    PVOID Unused1[3];
    ULONG KernelReserved[15];
    ULONG SecondLevelCacheSize;
    ULONG HalReserved[16];
    ULONG Unused2;
    PVOID KdVersionBlock;
    PVOID Unused3;
    ULONG PcrAlign1[24];
} KPCR, *PKPCR;

经常会有这样的使用方式：

mov eax, fs:[0];

mov ecx, dword ptr [ eax ];

这里访问的是PCB的第一个成员，就是线程控制块的第一个成员变量，就是ExceptionList，SEH异常控制块链表。

它的结构定义是：

typedef struct _NT_TIB {
  struct _EXCEPTION_REGISTRATION_RECORD *ExceptionList; //最常使用的异常控制块链表
  PVOID StackBase;
  PVOID StackLimit;
  PVOID SubSystemTib;
  _ANONYMOUS_UNION union {
    PVOID FiberData;
    ULONG Version;
  } DUMMYUNIONNAME;
  PVOID ArbitraryUserPointer;
  struct _NT_TIB *Self;
} NT_TIB, *PNT_TIB;

用户态下的TEB结构体的定义：

typedef struct _TEB {
    NT_TIB NtTib;
    PVOID  EnvironmentPointer;
    CLIENT_ID ClientId;
    PVOID ActiveRpcHandle;
    PVOID ThreadLocalStoragePointer;
    PPEB ProcessEnvironmentBlock;
    ULONG LastErrorValue;
    ULONG CountOfOwnedCriticalSections;
    PVOID CsrClientThread;
    PVOID Win32ThreadInfo;          // PtiCurrent
    ULONG Win32ClientInfo[WIN32_CLIENT_INFO_LENGTH];    // User32 Client Info
    PVOID WOW32Reserved;           // used by WOW
    LCID CurrentLocale;
    ULONG FpSoftwareStatusRegister;
    PVOID SystemReserved1[54];      // Used by FP emulator
    PVOID Spare1;                   // unused
    NTSTATUS ExceptionCode;         // for RaiseUserException
    UCHAR SpareBytes1[40];
    PVOID SystemReserved2[10];                      // Used by user/console for temp obja
    GDI_TEB_BATCH GdiTebBatch;      // Gdi batching
    ULONG gdiRgn;
    ULONG gdiPen;
    ULONG gdiBrush;
    CLIENT_ID RealClientId;
    HANDLE GdiCachedProcessHandle;
    ULONG GdiClientPID;
    ULONG GdiClientTID;
    PVOID GdiThreadLocalInfo;
    PVOID UserReserved[5];          // unused
    PVOID glDispatchTable[280];     // OpenGL
    ULONG glReserved1[26];          // OpenGL
    PVOID glReserved2;              // OpenGL
    PVOID glSectionInfo;            // OpenGL
    PVOID glSection;                // OpenGL
    PVOID glTable;                  // OpenGL
    PVOID glCurrentRC;              // OpenGL
    PVOID glContext;                // OpenGL
    ULONG LastStatusValue;
    UNICODE_STRING StaticUnicodeString;
    WCHAR StaticUnicodeBuffer[STATIC_UNICODE_BUFFER_LENGTH];
    PVOID DeallocationStack;
    PVOID TlsSlots[TLS_MINIMUM_AVAILABLE];
    LIST_ENTRY TlsLinks;
    PVOID Vdm;
    PVOID ReservedForNtRpc;
    PVOID DbgSsReserved[2];
    ULONG HardErrorsAreDisabled;
    PVOID Instrumentation[16];
    PVOID WinSockData;              // WinSock
    ULONG GdiBatchCount;
    ULONG Spare2;
    ULONG Spare3;
    ULONG Spare4;
    PVOID ReservedForOle;
    ULONG WaitingOnLoaderLock;
} TEB;

它的成员ProcessEnvironmentBlock对应的PEB结构的定义：

typedef struct _PEB {
    BOOLEAN InheritedAddressSpace;      // These four fields cannot change unless the
    BOOLEAN ReadImageFileExecOptions;   //
    BOOLEAN BeingDebugged;              //
    BOOLEAN SpareBool;                  //
    HANDLE Mutant;                      // INITIAL_PEB structure is also updated.

    PVOID ImageBaseAddress;
    PPEB_LDR_DATA Ldr;
    struct _RTL_USER_PROCESS_PARAMETERS *ProcessParameters;
    PVOID SubSystemData;
    PVOID ProcessHeap;
    PVOID FastPebLock;
    PVOID FastPebLockRoutine;
    PVOID FastPebUnlockRoutine;
    ULONG EnvironmentUpdateCount;
    PVOID KernelCallbackTable;
    HANDLE EventLogSection;
    PVOID EventLog;
    PPEB_FREE_BLOCK FreeList;
    ULONG TlsExpansionCounter;
    PVOID TlsBitmap;
    ULONG TlsBitmapBits[2];         // relates to TLS_MINIMUM_AVAILABLE
    PVOID ReadOnlySharedMemoryBase;
    PVOID ReadOnlySharedMemoryHeap;
    PVOID *ReadOnlyStaticServerData;
    PVOID AnsiCodePageData;
    PVOID OemCodePageData;
    PVOID UnicodeCaseTableData;

    // Useful information for LdrpInitialize
    ULONG NumberOfProcessors;
    ULONG NtGlobalFlag;

    // Passed up from MmCreatePeb from Session Manager registry key

    LARGE_INTEGER CriticalSectionTimeout;
    ULONG HeapSegmentReserve;
    ULONG HeapSegmentCommit;
    ULONG HeapDeCommitTotalFreeThreshold;
    ULONG HeapDeCommitFreeBlockThreshold;

    // Where heap manager keeps track of all heaps created for a process
    // Fields initialized by MmCreatePeb.  ProcessHeaps is initialized
    // to point to the first free byte after the PEB and MaximumNumberOfHeaps
    // is computed from the page size used to hold the PEB, less the fixed
    // size of this data structure.

    ULONG NumberOfHeaps;
    ULONG MaximumNumberOfHeaps;
    PVOID *ProcessHeaps;

    //
    //
    PVOID GdiSharedHandleTable;
    PVOID ProcessStarterHelper;
    PVOID GdiDCAttributeList;
    PVOID LoaderLock;

    // Following fields filled in by MmCreatePeb from system values and/or
    // image header.

    ULONG OSMajorVersion;
    ULONG OSMinorVersion;
    ULONG OSBuildNumber;
    ULONG OSPlatformId;
    ULONG ImageSubsystem;
    ULONG ImageSubsystemMajorVersion;
    ULONG ImageSubsystemMinorVersion;
    ULONG ImageProcessAffinityMask;
    ULONG GdiHandleBuffer[GDI_HANDLE_BUFFER_SIZE];
} PEB, *PPEB;

真实的WINDOWS定义的形式为：

kd> dt ntkrnlpa!_KPCR
   +0x000 NtTib            : _NT_TIB
   +0x01c SelfPcr          : Ptr32 _KPCR
   +0x020 Prcb             : Ptr32 _KPRCB
   +0x024 Irql             : UChar
   +0x028 IRR              : Uint4B
   +0x02c IrrActive        : Uint4B
   +0x030 IDR              : Uint4B
   +0x034 KdVersionBlock   : Ptr32 Void
   +0x038 IDT              : Ptr32 _KIDTENTRY
   +0x03c GDT              : Ptr32 _KGDTENTRY
   +0x040 TSS              : Ptr32 _KTSS
   +0x044 MajorVersion     : Uint2B
   +0x046 MinorVersion     : Uint2B
   +0x048 SetMember        : Uint4B
   +0x04c StallScaleFactor : Uint4B
   +0x050 DebugActive      : UChar
   +0x051 Number           : UChar
   +0x052 Spare0           : UChar
   +0x053 SecondLevelCacheAssociativity : UChar
   +0x054 VdmAlert         : Uint4B
   +0x058 KernelReserved   : [14] Uint4B
   +0x090 SecondLevelCacheSize : Uint4B
   +0x094 HalReserved      : [16] Uint4B
   +0x0d4 InterruptMode    : Uint4B
   +0x0d8 Spare1           : UChar
   +0x0dc KernelReserved2  : [17] Uint4B
   +0x120 PrcbData         : _KPRCB

它的第3个成员Prcb的KPRCB结构的定义为：

dt ntkrnlpa!_KPRCB
   +0x000 MinorVersion     : Uint2B
   +0x002 MajorVersion     : Uint2B
   +0x004 CurrentThread    : Ptr32 _KTHREAD
   +0x008 NextThread       : Ptr32 _KTHREAD
   +0x00c IdleThread       : Ptr32 _KTHREAD
   +0x010 Number           : Char
   +0x011 Reserved         : Char
   +0x012 BuildType        : Uint2B
   +0x014 SetMember        : Uint4B
   +0x018 CpuType          : Char
   +0x019 CpuID            : Char
   +0x01a CpuStep          : Uint2B
   +0x01c ProcessorState   : _KPROCESSOR_STATE
   +0x33c KernelReserved   : [16] Uint4B
   +0x37c HalReserved      : [16] Uint4B
   +0x3bc PrcbPad0         : [92] UChar
   +0x418 LockQueue        : [16] _KSPIN_LOCK_QUEUE
   +0x498 PrcbPad1         : [8] UChar
   +0x4a0 NpxThread        : Ptr32 _KTHREAD
   +0x4a4 InterruptCount   : Uint4B
   +0x4a8 KernelTime       : Uint4B
   +0x4ac UserTime         : Uint4B
   +0x4b0 DpcTime          : Uint4B
   +0x4b4 DebugDpcTime     : Uint4B
   +0x4b8 InterruptTime    : Uint4B
   +0x4bc AdjustDpcThreshold : Uint4B
   +0x4c0 PageColor        : Uint4B
   +0x4c4 SkipTick         : Uint4B
   +0x4c8 MultiThreadSetBusy : UChar
   +0x4c9 Spare2           : [3] UChar
   +0x4cc ParentNode       : Ptr32 _KNODE
   +0x4d0 MultiThreadProcessorSet : Uint4B
   +0x4d4 MultiThreadSetMaster : Ptr32 _KPRCB
   +0x4d8 ThreadStartCount : [2] Uint4B
   +0x4e0 CcFastReadNoWait : Uint4B
   +0x4e4 CcFastReadWait   : Uint4B
   +0x4e8 CcFastReadNotPossible : Uint4B
   +0x4ec CcCopyReadNoWait : Uint4B
   +0x4f0 CcCopyReadWait   : Uint4B
   +0x4f4 CcCopyReadNoWaitMiss : Uint4B
   +0x4f8 KeAlignmentFixupCount : Uint4B
   +0x4fc KeContextSwitches : Uint4B
   +0x500 KeDcacheFlushCount : Uint4B
   +0x504 KeExceptionDispatchCount : Uint4B
   +0x508 KeFirstLevelTbFills : Uint4B
   +0x50c KeFloatingEmulationCount : Uint4B
   +0x510 KeIcacheFlushCount : Uint4B
   +0x514 KeSecondLevelTbFills : Uint4B
   +0x518 KeSystemCalls    : Uint4B
   +0x51c SpareCounter0    : [1] Uint4B
   +0x520 PPLookasideList  : [16] _PP_LOOKASIDE_LIST
   +0x5a0 PPNPagedLookasideList : [32] _PP_LOOKASIDE_LIST
   +0x6a0 PPPagedLookasideList : [32] _PP_LOOKASIDE_LIST
   +0x7a0 PacketBarrier    : Uint4B
   +0x7a4 ReverseStall     : Uint4B
   +0x7a8 IpiFrame         : Ptr32 Void
   +0x7ac PrcbPad2         : [52] UChar
   +0x7e0 CurrentPacket    : [3] Ptr32 Void
   +0x7ec TargetSet        : Uint4B
   +0x7f0 WorkerRoutine    : Ptr32     void
   +0x7f4 IpiFrozen        : Uint4B
   +0x7f8 PrcbPad3         : [40] UChar
   +0x820 RequestSummary   : Uint4B
   +0x824 SignalDone       : Ptr32 _KPRCB
   +0x828 PrcbPad4         : [56] UChar
   +0x860 DpcListHead      : _LIST_ENTRY
   +0x868 DpcStack         : Ptr32 Void
   +0x86c DpcCount         : Uint4B
   +0x870 DpcQueueDepth    : Uint4B
   +0x874 DpcRoutineActive : Uint4B
   +0x878 DpcInterruptRequested : Uint4B
   +0x87c DpcLastCount     : Uint4B
   +0x880 DpcRequestRate   : Uint4B
   +0x884 MaximumDpcQueueDepth : Uint4B
   +0x888 MinimumDpcRate   : Uint4B
   +0x88c QuantumEnd       : Uint4B
   +0x890 PrcbPad5         : [16] UChar
   +0x8a0 DpcLock          : Uint4B
   +0x8a4 PrcbPad6         : [28] UChar
   +0x8c0 CallDpc          : _KDPC
   +0x8e0 ChainedInterruptList : Ptr32 Void
   +0x8e4 LookasideIrpFloat : Int4B
   +0x8e8 SpareFields0     : [6] Uint4B
   +0x900 VendorString     : [13] UChar
   +0x90d InitialApicId    : UChar
   +0x90e LogicalProcessorsPerPhysicalProcessor : UChar
   +0x910 MHz              : Uint4B
   +0x914 FeatureBits      : Uint4B
   +0x918 UpdateSignature  : _LARGE_INTEGER
   +0x920 NpxSaveArea      : _FX_SAVE_AREA
   +0xb30 PowerState       : _PROCESSOR_POWER_STATE

第1个成员NtTib对应的NT_TIB结构定义如下：

nt!_NT_TIB
   +0x000 ExceptionList    : Ptr32 _EXCEPTION_REGISTRATION_RECORD
   +0x004 StackBase        : Ptr32 Void
   +0x008 StackLimit       : Ptr32 Void
   +0x00c SubSystemTib     : Ptr32 Void
   +0x010 FiberData        : Ptr32 Void
   +0x010 Version          : Uint4B
   +0x014 ArbitraryUserPointer : Ptr32 Void
   +0x018 Self             : Ptr32 _NT_TIB

在用户态环境下，fs:[0]对应的TEB结构定义：

dt nt!_TEB
   +0x000 NtTib            : _NT_TIB
   +0x01c EnvironmentPointer : Ptr32 Void
   +0x020 ClientId         : _CLIENT_ID
   +0x028 ActiveRpcHandle  : Ptr32 Void
   +0x02c ThreadLocalStoragePointer : Ptr32 Void
   +0x030 ProcessEnvironmentBlock : Ptr32 _PEB
   +0x034 LastErrorValue   : Uint4B
   +0x038 CountOfOwnedCriticalSections : Uint4B
   +0x03c CsrClientThread  : Ptr32 Void
   +0x040 Win32ThreadInfo  : Ptr32 Void
   +0x044 User32Reserved   : [26] Uint4B
   +0x0ac UserReserved     : [5] Uint4B
   +0x0c0 WOW32Reserved    : Ptr32 Void
   +0x0c4 CurrentLocale    : Uint4B
   +0x0c8 FpSoftwareStatusRegister : Uint4B
   +0x0cc SystemReserved1  : [54] Ptr32 Void
   +0x1a4 ExceptionCode    : Int4B
   +0x1a8 ActivationContextStack : _ACTIVATION_CONTEXT_STACK
   +0x1bc SpareBytes1      : [24] UChar
   +0x1d4 GdiTebBatch      : _GDI_TEB_BATCH
   +0x6b4 RealClientId     : _CLIENT_ID
   +0x6bc GdiCachedProcessHandle : Ptr32 Void
   +0x6c0 GdiClientPID     : Uint4B
   +0x6c4 GdiClientTID     : Uint4B
   +0x6c8 GdiThreadLocalInfo : Ptr32 Void
   +0x6cc Win32ClientInfo  : [62] Uint4B
   +0x7c4 glDispatchTable  : [233] Ptr32 Void
   +0xb68 glReserved1      : [29] Uint4B
   +0xbdc glReserved2      : Ptr32 Void
   +0xbe0 glSectionInfo    : Ptr32 Void
   +0xbe4 glSection        : Ptr32 Void
   +0xbe8 glTable          : Ptr32 Void
   +0xbec glCurrentRC      : Ptr32 Void
   +0xbf0 glContext        : Ptr32 Void
   +0xbf4 LastStatusValue  : Uint4B
   +0xbf8 StaticUnicodeString : _UNICODE_STRING
   +0xc00 StaticUnicodeBuffer : [261] Uint2B
   +0xe0c DeallocationStack : Ptr32 Void
   +0xe10 TlsSlots         : [64] Ptr32 Void
   +0xf10 TlsLinks         : _LIST_ENTRY
   +0xf18 Vdm              : Ptr32 Void
   +0xf1c ReservedForNtRpc : Ptr32 Void
   +0xf20 DbgSsReserved    : [2] Ptr32 Void
   +0xf28 HardErrorsAreDisabled : Uint4B
   +0xf2c Instrumentation  : [16] Ptr32 Void
   +0xf6c WinSockData      : Ptr32 Void
   +0xf70 GdiBatchCount    : Uint4B
   +0xf74 InDbgPrint       : UChar
   +0xf75 FreeStackOnTermination : UChar
   +0xf76 HasFiberData     : UChar
   +0xf77 IdealProcessor   : UChar
   +0xf78 Spare3           : Uint4B
   +0xf7c ReservedForPerf  : Ptr32 Void
   +0xf80 ReservedForOle   : Ptr32 Void
   +0xf84 WaitingOnLoaderLock : Uint4B
   +0xf88 Wx86Thread       : _Wx86ThreadState
   +0xf94 TlsExpansionSlots : Ptr32 Ptr32 Void
   +0xf98 ImpersonationLocale : Uint4B
   +0xf9c IsImpersonating  : Uint4B
   +0xfa0 NlsCache         : Ptr32 Void
   +0xfa4 pShimData        : Ptr32 Void
   +0xfa8 HeapVirtualAffinity : Uint4B
   +0xfac CurrentTransactionHandle : Ptr32 Void
   +0xfb0 ActiveFrame      : Ptr32 _TEB_ACTIVE_FRAME
   +0xfb4 SafeThunkCall    : UChar
   +0xfb5 BooleanSpare     : [3] UChar

它的成员ProcessEnvironmentBlock对应的_PEB结构的定义：

nt!_PEB
   +0x000 InheritedAddressSpace : UChar
   +0x001 ReadImageFileExecOptions : UChar
   +0x002 BeingDebugged    : UChar
   +0x003 SpareBool        : UChar
   +0x004 Mutant           : Ptr32 Void
   +0x008 ImageBaseAddress : Ptr32 Void
   +0x00c Ldr              : Ptr32 _PEB_LDR_DATA
   +0x010 ProcessParameters : Ptr32 _RTL_USER_PROCESS_PARAMETERS
   +0x014 SubSystemData    : Ptr32 Void
   +0x018 ProcessHeap      : Ptr32 Void
   +0x01c FastPebLock      : Ptr32 _RTL_CRITICAL_SECTION
   +0x020 FastPebLockRoutine : Ptr32 Void
   +0x024 FastPebUnlockRoutine : Ptr32 Void
   +0x028 EnvironmentUpdateCount : Uint4B
   +0x02c KernelCallbackTable : Ptr32 Void
   +0x030 SystemReserved   : [1] Uint4B
   +0x034 AtlThunkSListPtr32 : Uint4B
   +0x038 FreeList         : Ptr32 _PEB_FREE_BLOCK
   +0x03c TlsExpansionCounter : Uint4B
   +0x040 TlsBitmap        : Ptr32 Void
   +0x044 TlsBitmapBits    : [2] Uint4B
   +0x04c ReadOnlySharedMemoryBase : Ptr32 Void
   +0x050 ReadOnlySharedMemoryHeap : Ptr32 Void
   +0x054 ReadOnlyStaticServerData : Ptr32 Ptr32 Void
   +0x058 AnsiCodePageData : Ptr32 Void
   +0x05c OemCodePageData  : Ptr32 Void
   +0x060 UnicodeCaseTableData : Ptr32 Void
   +0x064 NumberOfProcessors : Uint4B
   +0x068 NtGlobalFlag     : Uint4B
   +0x070 CriticalSectionTimeout : _LARGE_INTEGER
   +0x078 HeapSegmentReserve : Uint4B
   +0x07c HeapSegmentCommit : Uint4B
   +0x080 HeapDeCommitTotalFreeThreshold : Uint4B
   +0x084 HeapDeCommitFreeBlockThreshold : Uint4B
   +0x088 NumberOfHeaps    : Uint4B
   +0x08c MaximumNumberOfHeaps : Uint4B
   +0x090 ProcessHeaps     : Ptr32 Ptr32 Void
   +0x094 GdiSharedHandleTable : Ptr32 Void
   +0x098 ProcessStarterHelper : Ptr32 Void
   +0x09c GdiDCAttributeList : Uint4B
   +0x0a0 LoaderLock       : Ptr32 Void
   +0x0a4 OSMajorVersion   : Uint4B
   +0x0a8 OSMinorVersion   : Uint4B
   +0x0ac OSBuildNumber    : Uint2B
   +0x0ae OSCSDVersion     : Uint2B
   +0x0b0 OSPlatformId     : Uint4B
   +0x0b4 ImageSubsystem   : Uint4B
   +0x0b8 ImageSubsystemMajorVersion : Uint4B
   +0x0bc ImageSubsystemMinorVersion : Uint4B
   +0x0c0 ImageProcessAffinityMask : Uint4B
   +0x0c4 GdiHandleBuffer  : [34] Uint4B
   +0x14c PostProcessInitRoutine : Ptr32     void
   +0x150 TlsExpansionBitmap : Ptr32 Void
   +0x154 TlsExpansionBitmapBits : [32] Uint4B
   +0x1d4 SessionId        : Uint4B
   +0x1d8 AppCompatFlags   : _ULARGE_INTEGER
   +0x1e0 AppCompatFlagsUser : _ULARGE_INTEGER
   +0x1e8 pShimData        : Ptr32 Void
   +0x1ec AppCompatInfo    : Ptr32 Void
   +0x1f0 CSDVersion       : _UNICODE_STRING
   +0x1f8 ActivationContextData : Ptr32 Void
   +0x1fc ProcessAssemblyStorageMap : Ptr32 Void
   +0x200 SystemDefaultActivationContextData : Ptr32 Void
   +0x204 SystemAssemblyStorageMap : Ptr32 Void
   +0x208 MinimumStackCommit : Uint4B

使用以上信息来查询相关的数据访问指令，可以搞清楚操作的含义。