CPU相信大家都知道是啥玩意，哪三個單詞縮寫。GDT對于一些不搞底層的人知道的可能還有一些。
GDT就是global descriptor table的縮寫。相應的還有個local descriptor tables (LDT)，這個不再此文的討論范圍內。
這在保護模式教程中經常看到，但是這和咱們程序員有啥關系呢？ 1.留后門
就是進入R0后設置（R3）進入R0的后門（如：調用門，中斷門，任務門等）。
2.了解/編寫操作系統
人家微軟的Windows操作系統經歷了很多變化，如今到了WIN10。（對于天天研究Windows的人）這對咱有意思嗎？頂多認識了解和應用/利用。 好像有不少的變化（PC端）都是基于硬件的。基于軟件的算法不說。
3.虛擬化
如：intel-VT就要設置許多段（如：cs,ss,ds,es,fs,gs等）的Base，Limit，access rights，Selectors等。
好了，廢話不多進入正題。
以Windows系統為例進行分析。
kd> vertarget
Windows XP Kernel Version 2600 (Service Pack 3) MP (1 procs) Free x86 compatible
Built by: 2600.xpsp_sp3_qfe.130704-0421
Machine Name:
Kernel base = 0x804d8000 PsLoadedModuleList = 0x8055e720
Debug session time: Thu Aug 6 14:25:16.468 2015 (UTC + 8:00)
System Uptime: 0 days 0:01:19.984
這是操作系統的環境信息。
GDT是由GDTR指向的。
kd> r gdtr
gdtr=8003f000
其大小為：
kd> r gdtl
gdtl=000003ff
其全部的內容為：
kd> db 8003f000 L(000003ff + 1)
8003f000 00 00 00 00 00 00 00 00-ff ff 00 00 00 9b cf 00 ................
8003f010 ff ff 00 00 00 93 cf 00-ff ff 00 00 00 fb cf 00 ................
8003f020 ff ff 00 00 00 f3 cf 00-ab 20 00 20 04 8b 00 80 ......... . ....
8003f030 01 00 00 f0 df 93 c0 ff-ff 0f 00 00 00 f3 40 00 ..............@.
8003f040 ff ff 00 04 00 f2 00 00-00 00 00 00 00 00 00 00 ................
8003f050 68 00 00 27 55 89 00 80-68 00 68 27 55 89 00 80 h..'U...h.h'U...
8003f060 ff ff 40 2f 02 93 00 00-ff 3f 00 80 0b 92 00 00 ..@/.....?......
8003f070 ff 03 00 70 ff 92 00 ff-ff ff 00 00 40 9a 00 80 ...p........@...
8003f080 ff ff 00 00 40 92 00 80-00 00 00 00 00 92 00 00 ....@...........
8003f090 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
8003f0a0 68 00 b8 16 38 89 00 82-00 00 00 00 00 00 00 00 h...8...........
8003f0b0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
8003f0c0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
8003f0d0 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
8003f0e0 ff ff 00 f0 50 9f 00 f8-ff ff 00 00 00 92 00 00 ....P...........
8003f0f0 b7 03 40 d0 4f 98 00 80-ff ff 00 00 00 92 00 00 ..@.O...........
8003f100 ff ff 00 24 4d 93 40 ba-ff ff 00 24 4d 93 40 ba ...$M.@....$M.@.
8003f110 ff ff 00 24 4d 93 40 ba-20 f1 03 80 00 00 00 00 ...$M.@. .......
8003f120 28 f1 03 80 00 00 00 00-30 f1 03 80 00 00 00 00 (.......0.......
8003f130 38 f1 03 80 00 00 00 00-40 f1 03 80 00 00 00 00 8.......@.......
8003f140 48 f1 03 80 00 00 00 00-50 f1 03 80 00 00 00 00 H.......P.......
8003f150 58 f1 03 80 00 00 00 00-60 f1 03 80 00 00 00 00 X.......`.......
8003f160 68 f1 03 80 00 00 00 00-70 f1 03 80 00 00 00 00 h.......p.......
8003f170 78 f1 03 80 00 00 00 00-80 f1 03 80 00 00 00 00 x...............
8003f180 88 f1 03 80 00 00 00 00-90 f1 03 80 00 00 00 00 ................
8003f190 98 f1 03 80 00 00 00 00-a0 f1 03 80 00 00 00 00 ................
8003f1a0 a8 f1 03 80 00 00 00 00-b0 f1 03 80 00 00 00 00 ................
8003f1b0 b8 f1 03 80 00 00 00 00-c0 f1 03 80 00 00 00 00 ................
8003f1c0 c8 f1 03 80 00 00 00 00-d0 f1 03 80 00 00 00 00 ................
8003f1d0 d8 f1 03 80 00 00 00 00-e0 f1 03 80 00 00 00 00 ................
8003f1e0 e8 f1 03 80 00 00 00 00-f0 f1 03 80 00 00 00 00 ................
8003f1f0 f8 f1 03 80 00 00 00 00-00 f2 03 80 00 00 00 00 ................
8003f200 08 f2 03 80 00 00 00 00-10 f2 03 80 00 00 00 00 ................
8003f210 18 f2 03 80 00 00 00 00-20 f2 03 80 00 00 00 00 ........ .......
8003f220 28 f2 03 80 00 00 00 00-30 f2 03 80 00 00 00 00 (.......0.......
8003f230 38 f2 03 80 00 00 00 00-40 f2 03 80 00 00 00 00 8.......@.......
8003f240 48 f2 03 80 00 00 00 00-50 f2 03 80 00 00 00 00 H.......P.......
8003f250 58 f2 03 80 00 00 00 00-60 f2 03 80 00 00 00 00 X.......`.......
8003f260 68 f2 03 80 00 00 00 00-70 f2 03 80 00 00 00 00 h.......p.......
8003f270 78 f2 03 80 00 00 00 00-80 f2 03 80 00 00 00 00 x...............
8003f280 88 f2 03 80 00 00 00 00-90 f2 03 80 00 00 00 00 ................
8003f290 98 f2 03 80 00 00 00 00-a0 f2 03 80 00 00 00 00 ................
8003f2a0 a8 f2 03 80 00 00 00 00-b0 f2 03 80 00 00 00 00 ................
8003f2b0 b8 f2 03 80 00 00 00 00-c0 f2 03 80 00 00 00 00 ................
8003f2c0 c8 f2 03 80 00 00 00 00-d0 f2 03 80 00 00 00 00 ................
8003f2d0 d8 f2 03 80 00 00 00 00-e0 f2 03 80 00 00 00 00 ................
8003f2e0 e8 f2 03 80 00 00 00 00-f0 f2 03 80 00 00 00 00 ................
8003f2f0 f8 f2 03 80 00 00 00 00-00 f3 03 80 00 00 00 00 ................
8003f300 08 f3 03 80 00 00 00 00-10 f3 03 80 00 00 00 00 ................
8003f310 18 f3 03 80 00 00 00 00-20 f3 03 80 00 00 00 00 ........ .......
8003f320 28 f3 03 80 00 00 00 00-30 f3 03 80 00 00 00 00 (.......0.......
8003f330 38 f3 03 80 00 00 00 00-40 f3 03 80 00 00 00 00 8.......@.......
8003f340 48 f3 03 80 00 00 00 00-50 f3 03 80 00 00 00 00 H.......P.......
8003f350 58 f3 03 80 00 00 00 00-60 f3 03 80 00 00 00 00 X.......`.......
8003f360 68 f3 03 80 00 00 00 00-70 f3 03 80 00 00 00 00 h.......p.......
8003f370 78 f3 03 80 00 00 00 00-80 f3 03 80 00 00 00 00 x...............
8003f380 88 f3 03 80 00 00 00 00-90 f3 03 80 00 00 00 00 ................
8003f390 98 f3 03 80 00 00 00 00-a0 f3 03 80 00 00 00 00 ................
8003f3a0 a8 f3 03 80 00 00 00 00-b0 f3 03 80 00 00 00 00 ................
8003f3b0 b8 f3 03 80 00 00 00 00-c0 f3 03 80 00 00 00 00 ................
8003f3c0 c8 f3 03 80 00 00 00 00-d0 f3 03 80 00 00 00 00 ................
8003f3d0 d8 f3 03 80 00 00 00 00-e0 f3 03 80 00 00 00 00 ................
8003f3e0 e8 f3 03 80 00 00 00 00-f0 f3 03 80 00 00 00 00 ................
8003f3f0 f8 f3 03 80 00 00 00 00-00 00 00 00 00 00 00 00 ................
注意：是8字節對齊并是8的整數倍。
不過這些數據不好看，要解析，這就是我們的任務。
其實也可以這樣看：
kd> dg 0 3ff
P Si Gr Pr Lo
Sel Base Limit Type l ze an es ng Flags
---- -------- -------- ---------- - -- -- -- -- --------
0000 00000000 00000000 <Reserved> 0 Nb By Np Nl 00000000
0008 00000000 ffffffff Code RE Ac 0 Bg Pg P Nl 00000c9b
0010 00000000 ffffffff Data RW Ac 0 Bg Pg P Nl 00000c93
0018 00000000 ffffffff Code RE Ac 3 Bg Pg P Nl 00000cfb
0020 00000000 ffffffff Data RW Ac 3 Bg Pg P Nl 00000cf3
0028 80042000 000020ab TSS32 Busy 0 Nb By P Nl 0000008b
0030 ffdff000 00001fff Data RW Ac 0 Bg Pg P Nl 00000c93
0038 00000000 00000fff Data RW Ac 3 Bg By P Nl 000004f3
0040 00000400 0000ffff Data RW 3 Nb By P Nl 000000f2
0048 00000000 00000000 <Reserved> 0 Nb By Np Nl 00000000
0050 80552700 00000068 TSS32 Avl 0 Nb By P Nl 00000089
0058 80552768 00000068 TSS32 Avl 0 Nb By P Nl 00000089
0060 00022f40 0000ffff Data RW Ac 0 Nb By P Nl 00000093
0068 000b8000 00003fff Data RW 0 Nb By P Nl 00000092
0070 ffff7000 000003ff Data RW 0 Nb By P Nl 00000092
0078 80400000 0000ffff Code RE 0 Nb By P Nl 0000009a
0080 80400000 0000ffff Data RW 0 Nb By P Nl 00000092
0088 00000000 00000000 Data RW 0 Nb By P Nl 00000092
0090 00000000 00000000 <Reserved> 0 Nb By Np Nl 00000000
0098 00000000 00000000 <Reserved> 0 Nb By Np Nl 00000000
00A0 823816b8 00000068 TSS32 Avl 0 Nb By P Nl 00000089
00A8 00000000 00000000 <Reserved> 0 Nb By Np Nl 00000000
00B0 00000000 00000000 <Reserved> 0 Nb By Np Nl 00000000
00B8 00000000 00000000 <Reserved> 0 Nb By Np Nl 00000000
00C0 00000000 00000000 <Reserved> 0 Nb By Np Nl 00000000
00C8 00000000 00000000 <Reserved> 0 Nb By Np Nl 00000000
00D0 00000000 00000000 <Reserved> 0 Nb By Np Nl 00000000
00D8 00000000 00000000 <Reserved> 0 Nb By Np Nl 00000000
00E0 f850f000 0000ffff Code RE Ac 0 Nb By P Nl 0000009f
00E8 00000000 0000ffff Data RW 0 Nb By P Nl 00000092
00F0 804fd040 000003b7 Code EO 0 Nb By P Nl 00000098
00F8 00000000 0000ffff Data RW 0 Nb By P Nl 00000092
0100 ba4d2400 0000ffff Data RW Ac 0 Bg By P Nl 00000493
0108 ba4d2400 0000ffff Data RW Ac 0 Bg By P Nl 00000493
0110 ba4d2400 0000ffff Data RW Ac 0 Bg By P Nl 00000493
0118 00008003 0000f120 <Reserved> 0 Nb By Np Nl 00000000
0120 00008003 0000f128 <Reserved> 0 Nb By Np Nl 00000000
0128 00008003 0000f130 <Reserved> 0 Nb By Np Nl 00000000
0130 00008003 0000f138 <Reserved> 0 Nb By Np Nl 00000000
0138 00008003 0000f140 <Reserved> 0 Nb By Np Nl 00000000
0140 00008003 0000f148 <Reserved> 0 Nb By Np Nl 00000000
0148 00008003 0000f150 <Reserved> 0 Nb By Np Nl 00000000
0150 00008003 0000f158 <Reserved> 0 Nb By Np Nl 00000000
0158 00008003 0000f160 <Reserved> 0 Nb By Np Nl 00000000
0160 00008003 0000f168 <Reserved> 0 Nb By Np Nl 00000000
0168 00008003 0000f170 <Reserved> 0 Nb By Np Nl 00000000
0170 00008003 0000f178 <Reserved> 0 Nb By Np Nl 00000000
0178 00008003 0000f180 <Reserved> 0 Nb By Np Nl 00000000
0180 00008003 0000f188 <Reserved> 0 Nb By Np Nl 00000000
0188 00008003 0000f190 <Reserved> 0 Nb By Np Nl 00000000
0190 00008003 0000f198 <Reserved> 0 Nb By Np Nl 00000000
0198 00008003 0000f1a0 <Reserved> 0 Nb By Np Nl 00000000
01A0 00008003 0000f1a8 <Reserved> 0 Nb By Np Nl 00000000
01A8 00008003 0000f1b0 <Reserved> 0 Nb By Np Nl 00000000
01B0 00008003 0000f1b8 <Reserved> 0 Nb By Np Nl 00000000
01B8 00008003 0000f1c0 <Reserved> 0 Nb By Np Nl 00000000
01C0 00008003 0000f1c8 <Reserved> 0 Nb By Np Nl 00000000
01C8 00008003 0000f1d0 <Reserved> 0 Nb By Np Nl 00000000
01D0 00008003 0000f1d8 <Reserved> 0 Nb By Np Nl 00000000
01D8 00008003 0000f1e0 <Reserved> 0 Nb By Np Nl 00000000
01E0 00008003 0000f1e8 <Reserved> 0 Nb By Np Nl 00000000
01E8 00008003 0000f1f0 <Reserved> 0 Nb By Np Nl 00000000
01F0 00008003 0000f1f8 <Reserved> 0 Nb By Np Nl 00000000
01F8 00008003 0000f200 <Reserved> 0 Nb By Np Nl 00000000
0200 00008003 0000f208 <Reserved> 0 Nb By Np Nl 00000000
0208 00008003 0000f210 <Reserved> 0 Nb By Np Nl 00000000
0210 00008003 0000f218 <Reserved> 0 Nb By Np Nl 00000000
0218 00008003 0000f220 <Reserved> 0 Nb By Np Nl 00000000
0220 00008003 0000f228 <Reserved> 0 Nb By Np Nl 00000000
0228 00008003 0000f230 <Reserved> 0 Nb By Np Nl 00000000
0230 00008003 0000f238 <Reserved> 0 Nb By Np Nl 00000000
0238 00008003 0000f240 <Reserved> 0 Nb By Np Nl 00000000
0240 00008003 0000f248 <Reserved> 0 Nb By Np Nl 00000000
0248 00008003 0000f250 <Reserved> 0 Nb By Np Nl 00000000
0250 00008003 0000f258 <Reserved> 0 Nb By Np Nl 00000000
0258 00008003 0000f260 <Reserved> 0 Nb By Np Nl 00000000
0260 00008003 0000f268 <Reserved> 0 Nb By Np Nl 00000000
0268 00008003 0000f270 <Reserved> 0 Nb By Np Nl 00000000
0270 00008003 0000f278 <Reserved> 0 Nb By Np Nl 00000000
0278 00008003 0000f280 <Reserved> 0 Nb By Np Nl 00000000
0280 00008003 0000f288 <Reserved> 0 Nb By Np Nl 00000000
0288 00008003 0000f290 <Reserved> 0 Nb By Np Nl 00000000
0290 00008003 0000f298 <Reserved> 0 Nb By Np Nl 00000000
0298 00008003 0000f2a0 <Reserved> 0 Nb By Np Nl 00000000
02A0 00008003 0000f2a8 <Reserved> 0 Nb By Np Nl 00000000
02A8 00008003 0000f2b0 <Reserved> 0 Nb By Np Nl 00000000
02B0 00008003 0000f2b8 <Reserved> 0 Nb By Np Nl 00000000
02B8 00008003 0000f2c0 <Reserved> 0 Nb By Np Nl 00000000
02C0 00008003 0000f2c8 <Reserved> 0 Nb By Np Nl 00000000
02C8 00008003 0000f2d0 <Reserved> 0 Nb By Np Nl 00000000
02D0 00008003 0000f2d8 <Reserved> 0 Nb By Np Nl 00000000
02D8 00008003 0000f2e0 <Reserved> 0 Nb By Np Nl 00000000
02E0 00008003 0000f2e8 <Reserved> 0 Nb By Np Nl 00000000
02E8 00008003 0000f2f0 <Reserved> 0 Nb By Np Nl 00000000
02F0 00008003 0000f2f8 <Reserved> 0 Nb By Np Nl 00000000
02F8 00008003 0000f300 <Reserved> 0 Nb By Np Nl 00000000
0300 00008003 0000f308 <Reserved> 0 Nb By Np Nl 00000000
0308 00008003 0000f310 <Reserved> 0 Nb By Np Nl 00000000
0310 00008003 0000f318 <Reserved> 0 Nb By Np Nl 00000000
0318 00008003 0000f320 <Reserved> 0 Nb By Np Nl 00000000
0320 00008003 0000f328 <Reserved> 0 Nb By Np Nl 00000000
0328 00008003 0000f330 <Reserved> 0 Nb By Np Nl 00000000
0330 00008003 0000f338 <Reserved> 0 Nb By Np Nl 00000000
0338 00008003 0000f340 <Reserved> 0 Nb By Np Nl 00000000
0340 00008003 0000f348 <Reserved> 0 Nb By Np Nl 00000000
0348 00008003 0000f350 <Reserved> 0 Nb By Np Nl 00000000
0350 00008003 0000f358 <Reserved> 0 Nb By Np Nl 00000000
0358 00008003 0000f360 <Reserved> 0 Nb By Np Nl 00000000
0360 00008003 0000f368 <Reserved> 0 Nb By Np Nl 00000000
0368 00008003 0000f370 <Reserved> 0 Nb By Np Nl 00000000
0370 00008003 0000f378 <Reserved> 0 Nb By Np Nl 00000000
0378 00008003 0000f380 <Reserved> 0 Nb By Np Nl 00000000
0380 00008003 0000f388 <Reserved> 0 Nb By Np Nl 00000000
0388 00008003 0000f390 <Reserved> 0 Nb By Np Nl 00000000
0390 00008003 0000f398 <Reserved> 0 Nb By Np Nl 00000000
0398 00008003 0000f3a0 <Reserved> 0 Nb By Np Nl 00000000
03A0 00008003 0000f3a8 <Reserved> 0 Nb By Np Nl 00000000
03A8 00008003 0000f3b0 <Reserved> 0 Nb By Np Nl 00000000
03B0 00008003 0000f3b8 <Reserved> 0 Nb By Np Nl 00000000
03B8 00008003 0000f3c0 <Reserved> 0 Nb By Np Nl 00000000
03C0 00008003 0000f3c8 <Reserved> 0 Nb By Np Nl 00000000
03C8 00008003 0000f3d0 <Reserved> 0 Nb By Np Nl 00000000
03D0 00008003 0000f3d8 <Reserved> 0 Nb By Np Nl 00000000
03D8 00008003 0000f3e0 <Reserved> 0 Nb By Np Nl 00000000
03E0 00008003 0000f3e8 <Reserved> 0 Nb By Np Nl 00000000
03E8 00008003 0000f3f0 <Reserved> 0 Nb By Np Nl 00000000
03F0 00008003 0000f3f8 <Reserved> 0 Nb By Np Nl 00000000
03F8 00000000 00000000 <Reserved> 0 Nb By Np Nl 00000000
我們的功能就是要解析出這樣的格式。
注意，另外一個話題是：也可以手動分析出這個格式，如：
kd> r cs
cs=00000008
然后根據一定的算法得出的結論要如下（一種思路是根據_KGDTENTRY的定義）：
kd> dg cs
P Si Gr Pr Lo
Sel Base Limit Type l ze an es ng Flags
---- -------- -------- ---------- - -- -- -- -- --------
0008 00000000 ffffffff Code RE Ac 0 Bg Pg P Nl 00000c9b
這個算法就不說了，相信你會的。
簡單說下吧！
GDT就是一個（數組格式的）表，里面的每一項是一個Segment Descriptors。
關于這個的格式，可見： Intel? 64 and IA-32 Architectures Software Developer’s Manual（Order Number: 325462-055US June 2015）的 Volume 3: System Programming Guide 的 3.4.5 Segment Descriptors小節及附圖。
這個Segment Descriptors具體的分兩大類：
一類是：application (code or data) descriptor。 這就是常見的代碼/數據段，如：大多數的CS，DS都指向這里。 一類是：system descriptor
這里又分為：system-segment descriptors（LDT and TSS segments）。 gate descriptors（call, interrupt, and trap gates）。
但是，這些結構在Windows下的定義是啥樣呢？
經查WRK和WINDBG，結果如下：
// Special Registers for i386
typedef struct _X86_DESCRIPTOR {
USHORT Pad;
USHORT Limit;
ULONG Base;
} X86_DESCRIPTOR, *PX86_DESCRIPTOR;
// GDT Entry
typedef struct _KGDTENTRY {
USHORT LimitLow;
USHORT BaseLow;
union {
struct {
UCHAR BaseMid;
UCHAR Flags1; // Declare as bytes to avoid alignment
UCHAR Flags2; // Problems.
UCHAR BaseHi;
} Bytes;
struct {
ULONG BaseMid : 8;
ULONG Type : 5;//把S位包含進去了，也就是是否為系統段描述符的位。
ULONG Dpl : 2;
ULONG Pres : 1;
ULONG LimitHi : 4;
ULONG Sys : 1;//即AVL，系統軟件自定義的。
ULONG Reserved_0 : 1;//LongMode
ULONG Default_Big : 1;//即INTEL的D/B (default operation size/default stack pointer size and/or upper bound) flag。
ULONG Granularity : 1;
ULONG BaseHi : 8;
} Bits;
} HighWord;
} KGDTENTRY, *PKGDTENTRY;
為啥定義的名字是KGDTENTRY呢？其實你想想結構的位置。 這個其實就是Segment Descriptors，但是定義的和INTEL的不完全一樣。
kd> dt nt!_KGDTENTRY
+0x000 LimitLow : Uint2B
+0x002 BaseLow : Uint2B
+0x004 HighWord : __unnamed
kd> dt nt!_KGDTENTRY -b
+0x000 LimitLow : Uint2B
+0x002 BaseLow : Uint2B
+0x004 HighWord : __unnamed
+0x000 Bytes : __unnamed
+0x000 BaseMid : UChar
+0x001 Flags1 : UChar
+0x002 Flags2 : UChar
+0x003 BaseHi : UChar
+0x000 Bits : __unnamed
+0x000 BaseMid : Pos 0, 8 Bits
+0x000 Type : Pos 8, 5 Bits
+0x000 Dpl : Pos 13, 2 Bits
+0x000 Pres : Pos 15, 1 Bit
+0x000 LimitHi : Pos 16, 4 Bits
+0x000 Sys : Pos 20, 1 Bit
+0x000 Reserved_0 : Pos 21, 1 Bit
+0x000 Default_Big : Pos 22, 1 Bit
+0x000 Granularity : Pos 23, 1 Bit
+0x000 BaseHi : Pos 24, 8 Bits
具體的算法請參見： 1.INTEL的資料。 2.WRK的算法。 3.本文的代碼。
上面分析的是32位下的Windows系統，再看看64位下Windows的GDT。
0: kd> vertarget
Windows 7 Kernel Version 7601 (Service Pack 1) MP (2 procs) Free x64
Built by: 7601.18869.amd64fre.win7sp1_gdr.150525-0603
Machine Name:
Kernel base = 0xfffff800`01e64000 PsLoadedModuleList = 0xfffff800`020ab730
Debug session time: Thu Aug 6 14:37:33.359 2015 (UTC + 8:00)
System Uptime: 0 days 0:13:15.757
0: kd> r gdtr
gdtr=fffff80001d51000
0: kd> r gdtl
gdtl=007f
0: kd> db fffff80001d51000 L(007f + 1)
fffff800`01d51000 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
fffff800`01d51010 00 00 00 00 00 9b 20 00-ff ff 00 00 00 93 cf 00 ...... .........
fffff800`01d51020 ff ff 00 00 00 fb cf 00-ff ff 00 00 00 f3 cf 00 ................
fffff800`01d51030 00 00 00 00 00 fb 20 00-00 00 00 00 00 00 00 00 ...... .........
fffff800`01d51040 67 00 80 20 d5 8b 00 01-00 f8 ff ff 00 00 00 00 g.. ............
fffff800`01d51050 00 3c 00 a0 f9 f3 40 ff-00 00 00 00 00 00 00 00 .<....@.........
fffff800`01d51060 ff ff 00 00 00 9a cf 00-00 00 00 00 00 00 00 00 ................
fffff800`01d51070 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
0: kd> dg 0 80
P Si Gr Pr Lo
Sel Base Limit Type l ze an es ng Flags
---- ----------------- ----------------- ---------- - -- -- -- -- --------
0000 00000000`00000000 00000000`00000000 <Reserved> 0 Nb By Np Nl 00000000
0008 00000000`00000000 00000000`00000000 <Reserved> 0 Nb By Np Nl 00000000
0010 00000000`00000000 00000000`00000000 Code RE Ac 0 Nb By P Lo 0000029b
0018 00000000`00000000 00000000`ffffffff Data RW Ac 0 Bg Pg P Nl 00000c93
0020 00000000`00000000 00000000`ffffffff Code RE Ac 3 Bg Pg P Nl 00000cfb
0028 00000000`00000000 00000000`ffffffff Data RW Ac 3 Bg Pg P Nl 00000cf3
0030 00000000`00000000 00000000`00000000 Code RE Ac 3 Nb By P Lo 000002fb
0038 00000000`00000000 00000000`00000000 <Reserved> 0 Nb By Np Nl 00000000
0040 00000000`01d52080 00000000`00000067 TSS32 Busy 0 Nb By P Nl 0000008b
0048 00000000`0000ffff 00000000`0000f800 <Reserved> 0 Nb By Np Nl 00000000
0050 ffffffff`fff9a000 00000000`00003c00 Data RW Ac 3 Bg By P Nl 000004f3
0058 00000000`00000000 00000000`00000000 <Reserved> 0 Nb By Np Nl 00000000
0060 00000000`00000000 00000000`ffffffff Code RE 0 Bg Pg P Nl 00000c9a
0068 00000000`00000000 00000000`00000000 <Reserved> 0 Nb By Np Nl 00000000
0070 00000000`00000000 00000000`00000000 <Reserved> 0 Nb By Np Nl 00000000
0078 00000000`00000000 00000000`00000000 <Reserved> 0 Nb By Np Nl 00000000
0080 Unable to get descriptor
WRK及WINDBG的相關（驗證）信息如下：
// Special Registers for AMD64.
typedef struct _AMD64_DESCRIPTOR {
USHORT Pad[3];
USHORT Limit;
ULONG64 Base;
} AMD64_DESCRIPTOR, *PAMD64_DESCRIPTOR;
typedef union _KGDTENTRY64 {
struct {
USHORT LimitLow;
USHORT BaseLow;
union {
struct {
UCHAR BaseMiddle;
UCHAR Flags1;
UCHAR Flags2;
UCHAR BaseHigh;
} Bytes;
struct {
ULONG BaseMiddle : 8;
ULONG Type : 5;//把S位包含進去了，也就是是否為系統段描述符的位。
ULONG Dpl : 2;
ULONG Present : 1;
ULONG LimitHigh : 4;
ULONG System : 1;//即AVL，系統軟件自定義的。
ULONG LongMode : 1;
ULONG DefaultBig : 1;//即INTEL的D/B (default operation size/default stack pointer size and/or upper bound) flag。
ULONG Granularity : 1;
ULONG BaseHigh : 8;
} Bits;
};
//ULONG BaseUpper;
//ULONG MustBeZero;
};
//ULONG64 Alignment;
} KGDTENTRY64, *PKGDTENTRY64;
0: kd> dt _KGDTENTRY64
hal!_KGDTENTRY64
+0x000 LimitLow : Uint2B
+0x002 BaseLow : Uint2B
+0x004 Bytes : <unnamed-tag>
+0x004 Bits : <unnamed-tag>
+0x008 BaseUpper : Uint4B
+0x00c MustBeZero : Uint4B
+0x000 Alignment : Uint8B
0: kd> dt _KGDTENTRY64 -b
hal!_KGDTENTRY64
+0x000 LimitLow : Uint2B
+0x002 BaseLow : Uint2B
+0x004 Bytes : <unnamed-tag>
+0x000 BaseMiddle : UChar
+0x001 Flags1 : UChar
+0x002 Flags2 : UChar
+0x003 BaseHigh : UChar
+0x004 Bits : <unnamed-tag>
+0x000 BaseMiddle : Pos 0, 8 Bits
+0x000 Type : Pos 8, 5 Bits
+0x000 Dpl : Pos 13, 2 Bits
+0x000 Present : Pos 15, 1 Bit
+0x000 LimitHigh : Pos 16, 4 Bits
+0x000 System : Pos 20, 1 Bit
+0x000 LongMode : Pos 21, 1 Bit
+0x000 DefaultBig : Pos 22, 1 Bit
+0x000 Granularity : Pos 23, 1 Bit
+0x000 BaseHigh : Pos 24, 8 Bits
+0x008 BaseUpper : Uint4B
+0x00c MustBeZero : Uint4B
+0x000 Alignment : Uint8B
注意： 1.以上只分析一個CPU的情況，如果一個計算機有多個CPU要分別處理。
2.為了和WINDBG的DG命令處理/顯示的相似，特意根據INTEL的Table 3-1. Code- and Data-Segment Types，制作一個字符串數組。還有待改善。
3.GetGdtLimit的這個功能沒有相應的C代碼，只有匯編代碼（.asm文件），包括（X86和X64）。這個代碼就不附帶了，相信你能做到的。
最后只有代碼了，請看代碼：
/*
功能：顯示每個CPU的GDT信息。
注釋：一下結構摘自WRK。
made by correy.
QQ:112426112.
homepage:http://correy.webs.com 注釋：需翻墻，有的翻墻軟件也打不開。
2008年夏天開始學習CPU的保護模式。
2015.01.11起稿。
2015年夏修改存檔，盡管還有一些不完美的地方。
*/
#include <ntifs.h>
#include <windef.h>
#if defined(_AMD64_) || defined(_IA64_) //defined(_WIN64)
// Special Registers for AMD64.
typedef struct _AMD64_DESCRIPTOR {
USHORT Pad[3];
USHORT Limit;
ULONG64 Base;
} AMD64_DESCRIPTOR, *PAMD64_DESCRIPTOR;
typedef union _KGDTENTRY64 {
struct {
USHORT LimitLow;
USHORT BaseLow;
union {
struct {
UCHAR BaseMiddle;
UCHAR Flags1;
UCHAR Flags2;
UCHAR BaseHigh;
} Bytes;
struct {
ULONG BaseMiddle : 8;
ULONG Type : 5;//把S位包含進去了，也就是是否為系統段描述符的位。
ULONG Dpl : 2;
ULONG Present : 1;
ULONG LimitHigh : 4;
ULONG System : 1;//即AVL，系統軟件自定義的。
ULONG LongMode : 1;
ULONG DefaultBig : 1;//即INTEL的D/B (default operation size/default stack pointer size and/or upper bound) flag。
ULONG Granularity : 1;
ULONG BaseHigh : 8;
} Bits;
};
//ULONG BaseUpper;/*經觀察，64下的結構的長度是6字節，不是上面定義的16字節。*/
//ULONG MustBeZero;
};
//ULONG64 Alignment;
} KGDTENTRY64, *PKGDTENTRY64;
#else
// Special Registers for i386
typedef struct _X86_DESCRIPTOR {
USHORT Pad;
USHORT Limit;
ULONG Base;
} X86_DESCRIPTOR, *PX86_DESCRIPTOR;
// GDT Entry
typedef struct _KGDTENTRY {
USHORT LimitLow;
USHORT BaseLow;
union {
struct {
UCHAR BaseMid;
UCHAR Flags1; // Declare as bytes to avoid alignment
UCHAR Flags2; // Problems.
UCHAR BaseHi;
} Bytes;
struct {
ULONG BaseMid : 8;
ULONG Type : 5;//把S位包含進去了，也就是是否為系統段描述符的位。
ULONG Dpl : 2;
ULONG Pres : 1;
ULONG LimitHi : 4;
ULONG Sys : 1;//即AVL，系統軟件自定義的。
ULONG Reserved_0 : 1;//LongMode
ULONG Default_Big : 1;//即INTEL的D/B (default operation size/default stack pointer size and/or upper bound) flag。
ULONG Granularity : 1;
ULONG BaseHi : 8;
} Bits;
} HighWord;
} KGDTENTRY, *PKGDTENTRY;
#endif
/*
根據：Table 3-1. Code- and Data-Segment Types，仿照WINDBG的dg命令定義。
*/
char SegmentTypes[][256] = {
"<Reserved>",//Data Read-Only縮寫是：Data RO，也可認為是： <Reserved>。如果結構（UINT64）全部為零，也可認為是Reserved。
"Data RO AC",//Data Read-Only, accessed
"Data RW",//Data Read/Write
"Data RW AC",//Data Read/Write, accessed
"Data RO ED",//Data Read-Only, expand-down
"Data RO ED AC",//Data Read-Only, expand-down, accessed
"Data RW ED",//Data Read/Write, expand-down
"Data RW ED AC",//Data Read/Write, expand-down, accessed
"Code EO",//Code Execute-Only
"Code EO AC",//Code Execute-Only, accessed
"Code RE",//Code Execute/Read 加空格以便顯示的對齊。
"Code RE AC",//Code Execute/Read, accessed
"Code EO CO",//Code Execute-Only, conforming
"Code EO CO AC",//Code Execute-Only, conforming, accessed
"Code RE CO",//Code Execute/Read, conforming
"Code RE CO AC",//Code Execute/Read, conforming, accessed
"TSS32 Busy ",//這個也可顯示只要識別了TSS及內容。
"TSS32 Avl" //這個在X86上出現了。
};
DRIVER_UNLOAD DriverUnload;
VOID DriverUnload(__in PDRIVER_OBJECT DriverObject)
{
}
#ifdef _X86_
__forceinline PKPCR KeGetPcr (VOID)
{
return (PKPCR)__readfsdword(FIELD_OFFSET(KPCR, SelfPcr));
}
#endif
USHORT NTAPI GetGdtLimit ();//匯編函數。
#if defined(_WIN64)
void show_gdt(int i)
/*
i的取值可以是0.
*/
{
//SIZE_T IDTR;
//X86_DESCRIPTOR gdtr = {0};//A pointer to the memory location where the IDTR is stored.
//KGDTENTRY * GDT = 0;
USHORT GdtLimit = 0;
SIZE_T r = 0;
PVOID p = 0;
int index = 0;
int maximun = 0;
PKGDTENTRY64 pkgdte;
SIZE_T ISR = 0;
KeSetSystemAffinityThread(i + 1);
pkgdte = KeGetPcr()->GdtBase;//沒有__sgdt,也不用sgdt匯編指令的辦法。但是這個獲取的沒有長度。
GdtLimit = GetGdtLimit ();//一般等于0x7f.
KeRevertToUserAffinityThread();
//p = &gdtr.Limit;
//r = * (SIZE_T *)p;
//pkgdte = (PKGDTENTRY)r;
/*
其實直接：
maximun = (idtr.Base + 1) / sizeof(KIDTENTRY);
也可以。
maximun一般等于256.
*/
//if (gdtr.Pad % sizeof(KIDTENTRY) == 0) {
// maximun = gdtr.Pad / sizeof(KIDTENTRY);
//} else {
// maximun = gdtr.Pad / sizeof(KIDTENTRY);
// maximun++;
//}
//if (GdtLimit % sizeof(KGDTENTRY64) == 0) {
// maximun = GdtLimit / sizeof(KGDTENTRY64);
//} else {
// maximun = GdtLimit / sizeof(KGDTENTRY64);
// maximun++;//一般是128.
//}
maximun = (GdtLimit + 1) / sizeof(KGDTENTRY64);
/*
顯示格式：
CPU SN Sel Base Limit Type Pl Size Gran Pres Long Flags
--- -- ---- ----------------- ----------------- ---------- -- ---- ---- ---- ---- --------
注釋：CPU和SN是自己添加的。SN即Segment Name,如：CS，DS，FS等.
*/
KdPrint(("Sel Base Limit Type DPl Size Gran Pres Long Flags\n"));//CPU SN
KdPrint(("---- ---------------- ---------------- ------------- --- ---- ---- ---- ---- --------\n"));//--- --
KdPrint(("\n"));
for ( ;index < maximun ;index++ )
{
PKGDTENTRY64 pkgdte_t = &pkgdte[index];
SIZE_T Base = 0;
SIZE_T Limit = 0;
ULONG Type = 0;
char * size = NULL;
char * Granularity = NULL;
char * Present = NULL;
char * LongMode = NULL;
int Flags = 0;
Base = pkgdte_t->Bits.BaseHigh;
Base = (Base << 24);
Base += (pkgdte_t->BaseLow + (pkgdte_t->Bits.BaseMiddle << 16));
Limit = pkgdte_t->LimitLow + (pkgdte_t->Bits.LimitHigh << 16);
if (pkgdte_t->Bits.DefaultBig && Base)
{
//擴充高位為1.即F.
Base += 0xffffffff00000000;
}
if (pkgdte_t->Bits.DefaultBig && pkgdte_t->Bits.Granularity)
{
//擴充高位為1.即F.
SIZE_T t = Limit;
Limit = (Limit << 12);
Limit += PAGE_SIZE - 1;
}
Type = pkgdte_t->Bits.Type;
_bittestandreset(&Type, 4);//因為這個包含了S位，所以要清除這個位標志。
if (pkgdte_t->Bits.DefaultBig)
{
size = "Bg ";//Big 加空格是為了對齊顯示。
}
else
{
size = "Nb ";//Not Big 加空格是為了對齊顯示。
}
if (pkgdte_t->Bits.Granularity)
{
Granularity = "Pg ";//Page 加空格是為了對齊顯示。
}
else
{
Granularity = "By ";//Byte 加空格是為了對齊顯示。
}
if (pkgdte_t->Bits.Present)
{
Present = "P ";//Present 加空格是為了對齊顯示。
}
else
{
Present = "NP ";//NO Present 加空格是為了對齊顯示。
}
if (pkgdte_t->Bits.LongMode)
{
LongMode = "Lo ";//Long 加空格是為了對齊顯示。
}
else
{
LongMode = "Nl ";//NO long 加空格是為了對齊顯示。
}
Flags = (pkgdte_t->Bytes.Flags2 >> 4);//去掉Segment limit的那幾位。
Flags = Flags << 8;
Flags = Flags + pkgdte_t->Bytes.Flags1;
KdPrint(("%04x %p %p %13s %03x %s %s %s %s 0x%04x\n",
index * 8, //sizeof (KGDTENTRY)
Base,
Limit,
SegmentTypes[Type],
pkgdte_t->Bits.Dpl,
size,
Granularity,
Present,
LongMode,
Flags
));
}
}
#else
void show_gdt(int i)
/*
i的取值可以是0.
*/
{
//SIZE_T IDTR;
//X86_DESCRIPTOR gdtr = {0};//A pointer to the memory location where the IDTR is stored.
//KGDTENTRY * GDT = 0;
USHORT GdtLimit = 0;
SIZE_T r = 0;
PVOID p = 0;
int index = 0;
int maximun = 0;
PKGDTENTRY pkgdte;
SIZE_T ISR = 0;
KeSetSystemAffinityThread(i + 1);
pkgdte = KeGetPcr()->GDT;//沒有__sgdt,也不用sgdt匯編指令的辦法。但是這個獲取的沒有長度。
GdtLimit = GetGdtLimit ();//一般等于0x3ff.
KeRevertToUserAffinityThread();
//p = &gdtr.Limit;
//r = * (SIZE_T *)p;
//pkgdte = (PKGDTENTRY)r;
/*
其實直接：
maximun = (idtr.Base + 1) / sizeof(KIDTENTRY);
也可以。
maximun一般等于256.
*/
//if (gdtr.Pad % sizeof(KIDTENTRY) == 0) {
// maximun = gdtr.Pad / sizeof(KIDTENTRY);
//} else {
// maximun = gdtr.Pad / sizeof(KIDTENTRY);
// maximun++;
//}
if (GdtLimit % sizeof(KGDTENTRY) == 0) {
maximun = GdtLimit / sizeof(KGDTENTRY);
} else {
maximun = GdtLimit / sizeof(KGDTENTRY);
maximun++;//一般是128.
}
/*
顯示格式：
CPU SN Sel Base Limit Type Pl Size Gran Pres Long Flags
--- -- ---- ----------------- ----------------- ---------- -- ---- ---- ---- ---- --------
注釋：CPU和SN是自己添加的。SN即Segment Name,如：CS，DS，FS等.
*/
KdPrint(("Sel Base Limit Type DPl Size Gran Pres Long Flags\n"));//CPU SN
KdPrint(("---- -------- ------------- ------------- --- ---- ---- ---- ---- --------\n"));//--- --
KdPrint(("\n"));
for ( ;index < maximun ;index++ )
{
PKGDTENTRY pkgdte_t = &pkgdte[index];
SIZE_T Base = 0;
SIZE_T Limit = 0;
ULONG Type = 0;
char * size = NULL;
char * Granularity = NULL;
char * Present = NULL;
char * LongMode = NULL;
int Flags = 0;
//注意：0x38處的值不停的變化。
USHORT BaseLow = pkgdte_t->BaseLow;
ULONG BaseMid = pkgdte_t->HighWord.Bits.BaseMid;
ULONG BaseHi = pkgdte_t->HighWord.Bits.BaseHi;
Base = (BaseHi << 24) + (BaseMid << 16) + BaseLow;//其實用位與更快 | 。
if (pkgdte_t->HighWord.Bits.Granularity && BooleanFlagOn(pkgdte_t->HighWord.Bits.Type, 2 ) ) {//關于標志位及算法，見權威資料。
Limit = pkgdte_t->LimitLow + (pkgdte_t->HighWord.Bits.LimitHi << 16);
Limit *= PAGE_SIZE;
Limit += PAGE_SIZE - 1;
} else {
Limit = pkgdte_t->LimitLow + (pkgdte_t->HighWord.Bits.LimitHi << 16);
}
Type = pkgdte_t->HighWord.Bits.Type;
_bittestandreset(&Type, 4);//因為這個包含了S位，所以要清除這個位標志。
if (pkgdte_t->HighWord.Bits.Default_Big)
{
size = "Bg ";//Big 加空格是為了對齊顯示。
}
else
{
size = "Nb ";//Not Big 加空格是為了對齊顯示。
}
if (pkgdte_t->HighWord.Bits.Granularity)
{
Granularity = "Pg ";//Page 加空格是為了對齊顯示。
}
else
{
Granularity = "By ";//Byte 加空格是為了對齊顯示。
}
if (pkgdte_t->HighWord.Bits.Pres)
{
Present = "P ";//Present 加空格是為了對齊顯示。
}
else
{
Present = "NP ";//NO Present 加空格是為了對齊顯示。
}
if (pkgdte_t->HighWord.Bits.Reserved_0)
{
LongMode = "Lo ";//Long 加空格是為了對齊顯示。
}
else
{
LongMode = "Nl ";//NO long 加空格是為了對齊顯示。
}
Flags = (pkgdte_t->HighWord.Bytes.Flags2 >> 4);//去掉Segment limit的那幾位。
Flags = Flags << 8;
Flags = Flags + pkgdte_t->HighWord.Bytes.Flags1;
KdPrint(("%04x %p %p %13s %03x %s %s %s %s 0x%04x\n",
index * 8, //sizeof (KGDTENTRY)
Base,
Limit,
SegmentTypes[Type],
pkgdte_t->HighWord.Bits.Dpl,
size,
Granularity,
Present,
LongMode,
Flags
));
}
}
#endif
#pragma INITCODE
DRIVER_INITIALIZE DriverEntry;
NTSTATUS DriverEntry(__in struct _DRIVER_OBJECT * DriverObject, __in PUNICODE_STRING RegistryPath)
{
int i = 0;
KdBreakPoint();
DriverObject->DriverUnload = DriverUnload;
for ( ;i < KeNumberProcessors ;i++ )//KeQueryMaximumProcessorCount() KeGetCurrentProcessorNumber
{
show_gdt(i);
}
return STATUS_SUCCESS;
}
結果及驗證：
32位Windows的結果：
kd> g
Sel Base Limit Type DPl Size Gran Pres Long Flags
---- -------- ------------- ------------- --- ---- ---- ---- ---- --------
0000 00000000 00000000 <Reserved> 000 Nb By NP Nl 0x0000
0008 00000000 FFFFFFFF Code RE AC 000 Bg Pg P Nl 0x0c9b
0010 00000000 FFFFFFFF Data RW AC 000 Bg Pg P Nl 0x0c93
0018 00000000 FFFFFFFF Code RE AC 003 Bg Pg P Nl 0x0cfb
0020 00000000 FFFFFFFF Data RW AC 003 Bg Pg P Nl 0x0cf3
0028 80042000 000020AB Code RE AC 000 Nb By P Nl 0x008b
0030 FFDFF000 00001FFF Data RW AC 000 Bg Pg P Nl 0x0c93
0038 00000000 00000FFF Data RW AC 003 Bg By P Nl 0x04f3
0040 00000400 0000FFFF Data RW 003 Nb By P Nl 0x00f2
0048 00000000 00000000 <Reserved> 000 Nb By NP Nl 0x0000
0050 80552700 00000068 Code EO AC 000 Nb By P Nl 0x0089
0058 80552768 00000068 Code EO AC 000 Nb By P Nl 0x0089
0060 00022F40 0000FFFF Data RW AC 000 Nb By P Nl 0x0093
0068 000B8000 00003FFF Data RW 000 Nb By P Nl 0x0092
0070 FFFF7000 000003FF Data RW 000 Nb By P Nl 0x0092
0078 80400000 0000FFFF Code RE 000 Nb By P Nl 0x009a
0080 80400000 0000FFFF Data RW 000 Nb By P Nl 0x0092
0088 00000000 00000000 Data RW 000 Nb By P Nl 0x0092
0090 00000000 00000000 <Reserved> 000 Nb By NP Nl 0x0000
0098 00000000 00000000 <Reserved> 000 Nb By NP Nl 0x0000
00a0 823816B8 00000068 Code EO AC 000 Nb By P Nl 0x0089
00a8 00000000 00000000 <Reserved> 000 Nb By NP Nl 0x0000
00b0 00000000 00000000 <Reserved> 000 Nb By NP Nl 0x0000
00b8 00000000 00000000 <Reserved> 000 Nb By NP Nl 0x0000
00c0 00000000 00000000 <Reserved> 000 Nb By NP Nl 0x0000
00c8 00000000 00000000 <Reserved> 000 Nb By NP Nl 0x0000
00d0 00000000 00000000 <Reserved> 000 Nb By NP Nl 0x0000
00d8 00000000 00000000 <Reserved> 000 Nb By NP Nl 0x0000
00e0 F850F000 0000FFFF Code RE CO AC 000 Nb By P Nl 0x009f
00e8 00000000 0000FFFF Data RW 000 Nb By P Nl 0x0092
00f0 804FD040 000003B7 Code EO 000 Nb By P Nl 0x0098
00f8 00000000 0000FFFF Data RW 000 Nb By P Nl 0x0092
0100 BA4D2400 0000FFFF Data RW AC 000 Bg By P Nl 0x0493
0108 BA4D2400 0000FFFF Data RW AC 000 Bg By P Nl 0x0493
0110 BA4D2400 0000FFFF Data RW AC 000 Bg By P Nl 0x0493
0118 00008003 0000F120 <Reserved> 000 Nb By NP Nl 0x0000
0120 00008003 0000F128 <Reserved> 000 Nb By NP Nl 0x0000
0128 00008003 0000F130 <Reserved> 000 Nb By NP Nl 0x0000
0130 00008003 0000F138 <Reserved> 000 Nb By NP Nl 0x0000
0138 00008003 0000F140 <Reserved> 000 Nb By NP Nl 0x0000
0140 00008003 0000F148 <Reserved> 000 Nb By NP Nl 0x0000
0148 00008003 0000F150 <Reserved> 000 Nb By NP Nl 0x0000
0150 00008003 0000F158 <Reserved> 000 Nb By NP Nl 0x0000
0158 00008003 0000F160 <Reserved> 000 Nb By NP Nl 0x0000
0160 00008003 0000F168 <Reserved> 000 Nb By NP Nl 0x0000
0168 00008003 0000F170 <Reserved> 000 Nb By NP Nl 0x0000
0170 00008003 0000F178 <Reserved> 000 Nb By NP Nl 0x0000
0178 00008003 0000F180 <Reserved> 000 Nb By NP Nl 0x0000
0180 00008003 0000F188 <Reserved> 000 Nb By NP Nl 0x0000
0188 00008003 0000F190 <Reserved> 000 Nb By NP Nl 0x0000
0190 00008003 0000F198 <Reserved> 000 Nb By NP Nl 0x0000
0198 00008003 0000F1A0 <Reserved> 000 Nb By NP Nl 0x0000
01a0 00008003 0000F1A8 <Reserved> 000 Nb By NP Nl 0x0000
01a8 00008003 0000F1B0 <Reserved> 000 Nb By NP Nl 0x0000
01b0 00008003 0000F1B8 <Reserved> 000 Nb By NP Nl 0x0000
01b8 00008003 0000F1C0 <Reserved> 000 Nb By NP Nl 0x0000
01c0 00008003 0000F1C8 <Reserved> 000 Nb By NP Nl 0x0000
01c8 00008003 0000F1D0 <Reserved> 000 Nb By NP Nl 0x0000
01d0 00008003 0000F1D8 <Reserved> 000 Nb By NP Nl 0x0000
01d8 00008003 0000F1E0 <Reserved> 000 Nb By NP Nl 0x0000
01e0 00008003 0000F1E8 <Reserved> 000 Nb By NP Nl 0x0000
01e8 00008003 0000F1F0 <Reserved> 000 Nb By NP Nl 0x0000
01f0 00008003 0000F1F8 <Reserved> 000 Nb By NP Nl 0x0000
01f8 00008003 0000F200 <Reserved> 000 Nb By NP Nl 0x0000
0200 00008003 0000F208 <Reserved> 000 Nb By NP Nl 0x0000
0208 00008003 0000F210 <Reserved> 000 Nb By NP Nl 0x0000
0210 00008003 0000F218 <Reserved> 000 Nb By NP Nl 0x0000
0218 00008003 0000F220 <Reserved> 000 Nb By NP Nl 0x0000
0220 00008003 0000F228 <Reserved> 000 Nb By NP Nl 0x0000
0228 00008003 0000F230 <Reserved> 000 Nb By NP Nl 0x0000
0230 00008003 0000F238 <Reserved> 000 Nb By NP Nl 0x0000
0238 00008003 0000F240 <Reserved> 000 Nb By NP Nl 0x0000
0240 00008003 0000F248 <Reserved> 000 Nb By NP Nl 0x0000
0248 00008003 0000F250 <Reserved> 000 Nb By NP Nl 0x0000
0250 00008003 0000F258 <Reserved> 000 Nb By NP Nl 0x0000
0258 00008003 0000F260 <Reserved> 000 Nb By NP Nl 0x0000
0260 00008003 0000F268 <Reserved> 000 Nb By NP Nl 0x0000
0268 00008003 0000F270 <Reserved> 000 Nb By NP Nl 0x0000
0270 00008003 0000F278 <Reserved> 000 Nb By NP Nl 0x0000
0278 00008003 0000F280 <Reserved> 000 Nb By NP Nl 0x0000
0280 00008003 0000F288 <Reserved> 000 Nb By NP Nl 0x0000
0288 00008003 0000F290 <Reserved> 000 Nb By NP Nl 0x0000
0290 00008003 0000F298 <Reserved> 000 Nb By NP Nl 0x0000
0298 00008003 0000F2A0 <Reserved> 000 Nb By NP Nl 0x0000
02a0 00008003 0000F2A8 <Reserved> 000 Nb By NP Nl 0x0000
02a8 00008003 0000F2B0 <Reserved> 000 Nb By NP Nl 0x0000
02b0 00008003 0000F2B8 <Reserved> 000 Nb By NP Nl 0x0000
02b8 00008003 0000F2C0 <Reserved> 000 Nb By NP Nl 0x0000
02c0 00008003 0000F2C8 <Reserved> 000 Nb By NP Nl 0x0000
02c8 00008003 0000F2D0 <Reserved> 000 Nb By NP Nl 0x0000
02d0 00008003 0000F2D8 <Reserved> 000 Nb By NP Nl 0x0000
02d8 00008003 0000F2E0 <Reserved> 000 Nb By NP Nl 0x0000
02e0 00008003 0000F2E8 <Reserved> 000 Nb By NP Nl 0x0000
02e8 00008003 0000F2F0 <Reserved> 000 Nb By NP Nl 0x0000
02f0 00008003 0000F2F8 <Reserved> 000 Nb By NP Nl 0x0000
02f8 00008003 0000F300 <Reserved> 000 Nb By NP Nl 0x0000
0300 00008003 0000F308 <Reserved> 000 Nb By NP Nl 0x0000
0308 00008003 0000F310 <Reserved> 000 Nb By NP Nl 0x0000
0310 00008003 0000F318 <Reserved> 000 Nb By NP Nl 0x0000
0318 00008003 0000F320 <Reserved> 000 Nb By NP Nl 0x0000
0320 00008003 0000F328 <Reserved> 000 Nb By NP Nl 0x0000
0328 00008003 0000F330 <Reserved> 000 Nb By NP Nl 0x0000
0330 00008003 0000F338 <Reserved> 000 Nb By NP Nl 0x0000
0338 00008003 0000F340 <Reserved> 000 Nb By NP Nl 0x0000
0340 00008003 0000F348 <Reserved> 000 Nb By NP Nl 0x0000
0348 00008003 0000F350 <Reserved> 000 Nb By NP Nl 0x0000
0350 00008003 0000F358 <Reserved> 000 Nb By NP Nl 0x0000
0358 00008003 0000F360 <Reserved> 000 Nb By NP Nl 0x0000
0360 00008003 0000F368 <Reserved> 000 Nb By NP Nl 0x0000
0368 00008003 0000F370 <Reserved> 000 Nb By NP Nl 0x0000
0370 00008003 0000F378 <Reserved> 000 Nb By NP Nl 0x0000
0378 00008003 0000F380 <Reserved> 000 Nb By NP Nl 0x0000
0380 00008003 0000F388 <Reserved> 000 Nb By NP Nl 0x0000
0388 00008003 0000F390 <Reserved> 000 Nb By NP Nl 0x0000
0390 00008003 0000F398 <Reserved> 000 Nb By NP Nl 0x0000
0398 00008003 0000F3A0 <Reserved> 000 Nb By NP Nl 0x0000
03a0 00008003 0000F3A8 <Reserved> 000 Nb By NP Nl 0x0000
03a8 00008003 0000F3B0 <Reserved> 000 Nb By NP Nl 0x0000
03b0 00008003 0000F3B8 <Reserved> 000 Nb By NP Nl 0x0000
03b8 00008003 0000F3C0 <Reserved> 000 Nb By NP Nl 0x0000
03c0 00008003 0000F3C8 <Reserved> 000 Nb By NP Nl 0x0000
03c8 00008003 0000F3D0 <Reserved> 000 Nb By NP Nl 0x0000
03d0 00008003 0000F3D8 <Reserved> 000 Nb By NP Nl 0x0000
03d8 00008003 0000F3E0 <Reserved> 000 Nb By NP Nl 0x0000
03e0 00008003 0000F3E8 <Reserved> 000 Nb By NP Nl 0x0000
03e8 00008003 0000F3F0 <Reserved> 000 Nb By NP Nl 0x0000
03f0 00008003 0000F3F8 <Reserved> 000 Nb By NP Nl 0x0000
03f8 00000000 00000000 <Reserved> 000 Nb By NP Nl 0x0000
驗證，可以和前面的顯示做對比。
64位Windows的結果：
0: kd> g
Sel Base Limit Type DPl Size Gran Pres Long Flags
---- ---------------- ---------------- ------------- --- ---- ---- ---- ---- --------
0000 0000000000000000 0000000000000000 <Reserved> 000 Nb By NP Nl 0x0000
0008 0000000000000000 0000000000000000 <Reserved> 000 Nb By NP Nl 0x0000
0010 0000000000000000 0000000000000000 Code RE AC 000 Nb By P Lo 0x029b
0018 0000000000000000 00000000FFFFFFFF Data RW AC 000 Bg Pg P Nl 0x0c93
0020 0000000000000000 00000000FFFFFFFF Code RE AC 003 Bg Pg P Nl 0x0cfb
0028 0000000000000000 00000000FFFFFFFF Data RW AC 003 Bg Pg P Nl 0x0cf3
0030 0000000000000000 0000000000000000 Code RE AC 003 Nb By P Lo 0x02fb
0038 0000000000000000 0000000000000000 <Reserved> 000 Nb By NP Nl 0x0000
0040 0000000001D52080 0000000000000067 Code RE AC 000 Nb By P Nl 0x008b
0048 000000000000FFFF 000000000000F800 <Reserved> 000 Nb By NP Nl 0x0000
0050 FFFFFFFFFFFA0000 0000000000003C00 Data RW AC 003 Bg By P Nl 0x04f3
0058 0000000000000000 0000000000000000 <Reserved> 000 Nb By NP Nl 0x0000
0060 0000000000000000 00000000FFFFFFFF Code RE 000 Bg Pg P Nl 0x0c9a
0068 0000000000000000 0000000000000000 <Reserved> 000 Nb By NP Nl 0x0000
0070 0000000000000000 0000000000000000 <Reserved> 000 Nb By NP Nl 0x0000
0078 0000000000000000 0000000000000000 <Reserved> 000 Nb By NP Nl 0x0000
Sel Base Limit Type DPl Size Gran Pres Long Flags
---- ---------------- ---------------- ------------- --- ---- ---- ---- ---- --------
0000 0000000000000000 0000000000000000 <Reserved> 000 Nb By NP Nl 0x0000
0008 0000000000000000 0000000000000000 <Reserved> 000 Nb By NP Nl 0x0000
0010 0000000000000000 0000000000000000 Code RE AC 000 Nb By P Lo 0x029b
0018 0000000000000000 00000000FFFFFFFF Data RW AC 000 Bg Pg P Nl 0x0c93
0020 0000000000000000 00000000FFFFFFFF Code RE AC 003 Bg Pg P Nl 0x0cfb
0028 0000000000000000 00000000FFFFFFFF Data RW AC 003 Bg Pg P Nl 0x0cf3
0030 0000000000000000 0000000000000000 Code RE AC 003 Nb By P Lo 0x02fb
0038 0000000000000000 0000000000000000 <Reserved> 000 Nb By NP Nl 0x0000
0040 00000000009F7E40 0000000000000067 Code RE AC 000 Nb By P Nl 0x008b
0048 000000000000FFFF 000000000000F880 <Reserved> 000 Nb By NP Nl 0x0000
0050 FFFFFFFFFFFE0000 0000000000007C00 Data RW AC 003 Bg By P Nl 0x04f3
0058 0000000000000000 0000000000000000 <Reserved> 000 Nb By NP Nl 0x0000
0060 0000000000000000 00000000FFFFFFFF Code RE 000 Bg Pg P Nl 0x0c9a
0068 0000000000000000 0000000000000000 <Reserved> 000 Nb By NP Nl 0x0000
0070 0000000000000000 0000000000000000 <Reserved> 000 Nb By NP Nl 0x0000
0078 0000000000000000 0000000000000000 <Reserved> 000 Nb By NP Nl 0x0000
驗證，可以和前面（某個）的顯示做對比。
這里顯示2個，是因為有兩個CPU。
細心的你應該（從對比中）還會發現一些不足和不一樣的地方，期待你的改正，剩下的任務也就是你要改正的地方。
如：添加顯示CPU的個數，及段的名字（特別是系統段，各種門）等。
不當之處，敬請指出。