1
2 #include <stdio.h>
3 #include <errno.h>
4 #include <string.h>
5
6 /* Stuff from Wine. */
7
8 typedef unsigned short WORD; /* I guess */
9 typedef unsigned char BYTE;
10
11 typedef struct _LDT_ENTRY {
12 WORD LimitLow;
13 WORD BaseLow;
14 union {
15 struct {
16 BYTE BaseMid;
17 BYTE Flags1;
18 /*Declare as bytes to avoid alignment problems */
19 BYTE Flags2;
20 BYTE BaseHi;
21 } Bytes;
22 struct {
23 unsigned BaseMid : 8;
24 unsigned Type : 5;
25 unsigned Dpl : 2;
26 unsigned Pres : 1;
27 unsigned LimitHi : 4;
28 unsigned Sys : 1;
29 unsigned Reserved_0 : 1;
30 unsigned Default_Big : 1;
31 unsigned Granularity : 1;
32 unsigned BaseHi : 8;
33 } Bits;
34 } HighWord;
35 } LDT_ENTRY;
36
wine_ldt_get_base(const LDT_ENTRY * ent)37 inline static void *wine_ldt_get_base( const LDT_ENTRY *ent )
38 {
39 return (void *)(ent->BaseLow |
40 (unsigned long)ent->HighWord.Bits.BaseMid << 16 |
41 (unsigned long)ent->HighWord.Bits.BaseHi << 24);
42 }
wine_ldt_get_limit(const LDT_ENTRY * ent)43 inline static unsigned int wine_ldt_get_limit( const LDT_ENTRY *ent )
44 {
45 unsigned int limit = ent->LimitLow | (ent->HighWord.Bits.LimitHi << 16);
46 if (ent->HighWord.Bits.Granularity) limit = (limit << 12) | 0xfff;
47 return limit;
48 }
49
50
51 /* our copy of the ldt */
52 LDT_ENTRY ldt_copy[8192];
53
54 /* System call to set LDT entry. */
55 //extern int __modify_ldt (int, struct modify_ldt_ldt_s *, size_t);
56 extern int __modify_ldt (int, void *, size_t);
57
print_ldt(void)58 void print_ldt ( void )
59 {
60 int res;
61 res = __modify_ldt( 0, ldt_copy, 8192*sizeof(LDT_ENTRY) );
62 printf("got %d bytes\n", res );
63 perror("error is");
64 }
65
66 /* Structure passed on `modify_ldt' call. */
67 #define MODIFY_LDT_CONTENTS_DATA 0
68 #define MODIFY_LDT_CONTENTS_STACK 1
69 #define MODIFY_LDT_CONTENTS_CODE 2
70
71 struct modify_ldt_ldt_s
72 {
73 unsigned int entry_number;
74 unsigned long int base_addr;
75 unsigned int limit;
76 unsigned int seg_32bit:1;
77 unsigned int contents:2;
78 unsigned int read_exec_only:1;
79 unsigned int limit_in_pages:1;
80 unsigned int seg_not_present:1;
81 unsigned int useable:1;
82 unsigned int empty:25;
83 };
84
85 /* System call to set LDT entry. */
86 //extern int __modify_ldt (int, struct modify_ldt_ldt_s *, size_t);
87
set_ldt1(void * base)88 void set_ldt1 ( void* base )
89 {
90 int stat;
91 struct modify_ldt_ldt_s ldt_entry;
92
93 /* stop valgrind yelping about initialised holes in this struct. */
94 memset(&ldt_entry, 0, sizeof(ldt_entry));
95
96 ldt_entry.entry_number = 1;
97 ldt_entry.base_addr = (unsigned)base; //0x12345678;
98 ldt_entry.limit = 10;
99 ldt_entry.seg_32bit = 1;
100 ldt_entry.contents = MODIFY_LDT_CONTENTS_DATA;
101 ldt_entry.read_exec_only = 0;
102 ldt_entry.limit_in_pages = 0;
103 ldt_entry.seg_not_present = 0;
104 stat = __modify_ldt (1, &ldt_entry, sizeof (ldt_entry));
105 printf("stat = %d\n", stat);
106 }
107
108
ldt_seg_write(int ldt_entno,unsigned offset,unsigned val)109 void ldt_seg_write ( int ldt_entno, unsigned offset, unsigned val )
110 {
111 asm volatile("movl %2, %%eax\n\t"
112 "movl %1, %%edx\n\t"
113 "movl %0, %%fs\n\t"
114 "movl %%eax, %%fs:(%%edx)\t"
115 :
116 : "r" (7 /* LDT(TI), least privilege */ + (ldt_entno << 3)),
117 "r" (offset), "r" (val)
118 : "eax", "edx", "cc" );
119 }
120
main(void)121 int main ( void )
122 {
123 int i;
124 int arr[9];
125
126 for (i = 0; i < 9; i++) arr[i] = 11*i;
127
128 set_ldt1( &arr[4] );
129 print_ldt();
130
131 ldt_seg_write(1 /* ldt entry # */, 4 /* offset */, 4444);
132
133 for (i = 0; i < 9; i++) printf("%d ", arr[i]);
134 printf("\n");
135
136 return 0;
137 }
138
139