1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
|
/**
* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
* This file MUST be in main library because LDT must
* be modified before program creates first thread
* - avifile includes this file from C++ code
* and initializes it at the start of player!
*/
#include "ldt_keeper.h"
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>
#ifdef __linux__
#include <asm/unistd.h>
#include <asm/ldt.h>
#else
#if defined(__NetBSD__) || defined(__FreeBSD__) || defined(__OpenBSD__)
#include <machine/segments.h>
#include <machine/sysarch.h>
#endif
#ifdef __svr4__
#include <sys/segment.h>
#include <sys/sysi86.h>
/* solaris x86: add missing prototype for sysi86() */
#ifdef __cplusplus
extern "C" {
#endif
extern int sysi86(int, void*);
#ifdef __cplusplus
}
#endif
#ifndef NUMSYSLDTS /* SunOS 2.5.1 does not define NUMSYSLDTS */
#define NUMSYSLDTS 6 /* Let's hope the SunOS 5.8 value is OK */
#endif
#define TEB_SEL_IDX NUMSYSLDTS
#endif
#define LDT_ENTRIES 8192
#define LDT_ENTRY_SIZE 8
#pragma pack(4)
struct modify_ldt_ldt_s {
unsigned int entry_number;
unsigned long base_addr;
unsigned int limit;
unsigned int seg_32bit:1;
unsigned int contents:2;
unsigned int read_exec_only:1;
unsigned int limit_in_pages:1;
unsigned int seg_not_present:1;
unsigned int useable:1;
};
#define MODIFY_LDT_CONTENTS_DATA 0
#define MODIFY_LDT_CONTENTS_STACK 1
#define MODIFY_LDT_CONTENTS_CODE 2
#endif
/* user level (privilege level: 3) ldt (1<<2) segment selector */
#define LDT_SEL(idx) ((idx) << 3 | 1 << 2 | 3)
#ifndef TEB_SEL_IDX
#define TEB_SEL_IDX 1
#endif
#define TEB_SEL LDT_SEL(TEB_SEL_IDX)
/**
*
* This should be performed before we create first thread. See remarks
* for write_ldt(), linux/kernel/ldt.c.
*
*/
void* fs_seg = NULL;
static char* prev_struct = NULL;
/**
* here is a small logical problem with Restore for multithreaded programs -
* in C++ we use static class for this...
*/
#ifdef __cplusplus
extern "C"
#endif
void Setup_FS_Segment(void)
{
__asm__ __volatile__(
"movl %0,%%eax; movw %%ax, %%fs" : : "i" (TEB_SEL)
);
}
#ifdef __linux__
/* XXX: why is this routine from libc redefined here? */
/* NOTE: the redefined version ignores the count param, count is hardcoded as 16 */
static int LDT_Modify( int func, struct modify_ldt_ldt_s *ptr,
unsigned long count )
{
int res;
#ifdef __PIC__
__asm__ __volatile__( "pushl %%ebx\n\t"
"movl %2,%%ebx\n\t"
"int $0x80\n\t"
"popl %%ebx"
: "=a" (res)
: "0" (__NR_modify_ldt),
"r" (func),
"c" (ptr),
"d"(16)//sizeof(*ptr) from kernel point of view
:"esi" );
#else
__asm__ __volatile__("int $0x80"
: "=a" (res)
: "0" (__NR_modify_ldt),
"b" (func),
"c" (ptr),
"d"(16)
:"esi");
#endif /* __PIC__ */
if (res >= 0) return res;
errno = -res;
return -1;
}
#endif
#if defined(__NetBSD__) || defined(__FreeBSD__) || defined(__OpenBSD__)
static void LDT_EntryToBytes( unsigned long *buffer, const struct modify_ldt_ldt_s *content )
{
*buffer++ = ((content->base_addr & 0x0000ffff) << 16) |
(content->limit & 0x0ffff);
*buffer = (content->base_addr & 0xff000000) |
((content->base_addr & 0x00ff0000)>>16) |
(content->limit & 0xf0000) |
(content->contents << 10) |
((content->read_exec_only == 0) << 9) |
((content->seg_32bit != 0) << 22) |
((content->limit_in_pages != 0) << 23) |
0xf000;
}
#endif
void Setup_LDT_Keeper(void)
{
struct modify_ldt_ldt_s array;
int fd;
int ret;
if (fs_seg)
return;
prev_struct = 0;
fd = open("/dev/zero", O_RDWR);
if(fd<0){
perror( "Cannot open /dev/zero for READ+WRITE. Check permissions! error: " );
return;
}
fs_seg = mmap(NULL, getpagesize(), PROT_READ | PROT_WRITE, MAP_PRIVATE,
fd, 0);
if(fs_seg==(void*)-1)
{
perror("ERROR: Couldn't allocate memory for fs segment");
return;
}
// printf("fs seg %p\n", fs_seg);
*(void**)((char*)fs_seg+0x18) = fs_seg;
array.base_addr=(int)fs_seg;
array.entry_number=TEB_SEL_IDX;
array.limit=array.base_addr+getpagesize()-1;
array.seg_32bit=1;
array.read_exec_only=0;
array.seg_not_present=0;
array.contents=MODIFY_LDT_CONTENTS_DATA;
array.limit_in_pages=0;
#ifdef __linux__
ret=LDT_Modify(0x1, &array, sizeof(struct modify_ldt_ldt_s));
if(ret<0)
{
perror("install_fs");
printf("Couldn't install fs segment, expect segfault\n");
}
#endif /*linux*/
#if defined(__NetBSD__) || defined(__FreeBSD__) || defined(__OpenBSD__)
{
unsigned long d[2];
LDT_EntryToBytes( d, &array );
ret = i386_set_ldt(array.entry_number, (union descriptor *)d, 1);
if (ret < 0)
{
perror("install_fs");
printf("Couldn't install fs segment, expect segfault\n");
printf("Did you reconfigure the kernel with \"options USER_LDT\"?\n");
}
printf("Set_LDT\n");
}
#endif /* __NetBSD__ || __FreeBSD__ || __OpenBSD__ */
#if defined(__svr4__)
{
struct ssd ssd;
ssd.sel = TEB_SEL;
ssd.bo = array.base_addr;
ssd.ls = array.limit - array.base_addr;
ssd.acc1 = ((array.read_exec_only == 0) << 1) |
(array.contents << 2) |
0xf0; /* P(resent) | DPL3 | S */
ssd.acc2 = 0x4; /* byte limit, 32-bit segment */
if (sysi86(SI86DSCR, &ssd) < 0) {
perror("sysi86(SI86DSCR)");
printf("Couldn't install fs segment, expect segfault\n");
}
}
#endif
Setup_FS_Segment();
prev_struct = (char*)malloc(sizeof(char) * 8);
*(void**)array.base_addr = prev_struct;
close(fd);
}
void Restore_LDT_Keeper(void)
{
if (fs_seg == 0)
return;
if (prev_struct)
free(prev_struct);
munmap((char*)fs_seg, getpagesize());
fs_seg = 0;
}
|
