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#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 /* !__linux__ */
#if defined(__NetBSD__) || defined(__FreeBSD__) || defined(__OpenBSD__)
#include <machine/sysarch.h>
#endif
#ifdef __svr4__
#include <sys/segment.h>
#include <sys/sysi86.h>
/* solaris x86: add missing prototype for sysi86() */
extern int sysi86(int, void*);
#define TEB_SEL_IDX NUMSYSLDTS
#endif /* __svr4__ */
#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 /* !__linux__ */
#include "setup_FS.h"
/* 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)
void setup_FS_Segment()
{
#ifdef DETAILED_OUT
printf("Setup FS...");fflush(stdout);
#endif
__asm__ __volatile__(
"movl %0,%%eax; movw %%ax, %%fs" : : "i" (TEB_SEL)
);
#ifdef DETAILED_OUT
printf("OK!\n");
#endif
}
/**
*
* This should be performed before we create first thread. See remarks
* for write_ldt(), linux/kernel/ldt.c.
*
*/
static void* fs_seg=NULL;
#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 modify_ldt( 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(){
struct modify_ldt_ldt_s array;
int fd;
int ret;
void* prev_struct;
if(fs_seg) return; // already set!
fd=open("/dev/zero", O_RDWR);
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;
}
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=modify_ldt(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=malloc(8);
*(void**)array.base_addr=prev_struct;
close(fd);
}
void Restore_LDT_Keeper()
{
if(fs_seg==0) return;
munmap((char*)fs_seg, getpagesize());
}
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