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 
37 #if 0
38 inline static void *wine_ldt_get_base( const LDT_ENTRY *ent )
39 {
40     return (void *)(ent->BaseLow |
41                     (unsigned long)ent->HighWord.Bits.BaseMid << 16 |
42                     (unsigned long)ent->HighWord.Bits.BaseHi << 24);
43 }
44 inline static unsigned int wine_ldt_get_limit( const LDT_ENTRY *ent )
45 {
46     unsigned int limit = ent->LimitLow | (ent->HighWord.Bits.LimitHi << 16);
47     if (ent->HighWord.Bits.Granularity) limit = (limit << 12) | 0xfff;
48     return limit;
49 }
50 #endif
51 
52 /* our copy of the ldt */
53 LDT_ENTRY ldt_copy[8192];
54 
55 /* System call to set LDT entry.  */
56 //extern int __modify_ldt (int, struct modify_ldt_ldt_s *, size_t);
57 extern int __modify_ldt (int, void *, size_t);
58 
print_ldt(void)59 void print_ldt ( void )
60 {
61    int res;
62    res = __modify_ldt( 0, ldt_copy, 8192*sizeof(LDT_ENTRY) );
63    printf("got %d bytes\n", res );
64    perror("error is");
65 }
66 
67 /* Structure passed on `modify_ldt' call.  */
68 #define MODIFY_LDT_CONTENTS_DATA        0
69 #define MODIFY_LDT_CONTENTS_STACK       1
70 #define MODIFY_LDT_CONTENTS_CODE        2
71 
72 struct modify_ldt_ldt_s
73 {
74   unsigned int entry_number;
75   unsigned long int base_addr;
76   unsigned int limit;
77   unsigned int seg_32bit:1;
78   unsigned int contents:2;
79   unsigned int read_exec_only:1;
80   unsigned int limit_in_pages:1;
81   unsigned int seg_not_present:1;
82   unsigned int useable:1;
83   unsigned int empty:25;
84 };
85 
86 /* System call to set LDT entry.  */
87 //extern int __modify_ldt (int, struct modify_ldt_ldt_s *, size_t);
88 
set_ldt1(void * base)89 void set_ldt1 ( void* base )
90 {
91   int stat;
92   struct modify_ldt_ldt_s ldt_entry;
93 
94   /* stop valgrind yelping about initialised holes in this struct. */
95   memset(&ldt_entry, 0, sizeof(ldt_entry));
96 
97   ldt_entry.entry_number = 1;
98   ldt_entry.base_addr = (unsigned)base; //0x12345678;
99   ldt_entry.limit = 10;
100   ldt_entry.seg_32bit = 1;
101   ldt_entry.contents = MODIFY_LDT_CONTENTS_DATA;
102   ldt_entry.read_exec_only = 0;
103   ldt_entry.limit_in_pages = 0;
104   ldt_entry.seg_not_present = 0;
105   stat = __modify_ldt (1, &ldt_entry, sizeof (ldt_entry));
106   printf("stat = %d\n", stat);
107 }
108 
109 
ldt_seg_write(int ldt_entno,unsigned offset,unsigned val)110 void ldt_seg_write ( int ldt_entno, unsigned offset, unsigned val )
111 {
112   asm volatile("movl %2, %%eax\n\t"
113                "movl %1, %%edx\n\t"
114 	       "movl %0, %%fs\n\t"
115                "movl %%eax, %%fs:(%%edx)\t"
116 	       :
117                : "r" (7 /* LDT(TI), least privilege */ + (ldt_entno << 3)),
118                  "r" (offset), "r" (val)
119                : "eax", "edx", "cc" );
120 }
121 
main(void)122 int main ( void )
123 {
124   int i;
125   int arr[9];
126 
127   for (i = 0; i < 9; i++) arr[i] = 11*i;
128 
129   set_ldt1( &arr[4] );
130   print_ldt();
131 
132   ldt_seg_write(1 /* ldt entry # */, 4 /* offset */, 4444);
133 
134   for (i = 0; i < 9; i++) printf("%d ", arr[i]);
135   printf("\n");
136 
137   return 0;
138 }
139 
140