root/kernel/ldt.c

/* */

DEFINITIONS

1. read_ldt
2. write_ldt
3. sys_modify_ldt

   1 /*
   2  * linux/kernel/ldt.c
   3  *
   4  * Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
   5  */
   6 
   7 #include <linux/config.h>
   8 #include <linux/errno.h>
   9 #include <linux/sched.h>
  10 #include <linux/string.h>
  11 #include <asm/segment.h>
  12 #include <asm/system.h>
  13 #include <linux/ldt.h>
  14 
  15 static int read_ldt(void * ptr, unsigned long bytecount)
     /*  */
  16 {
  17         int error;
  18         void * address = current->ldt;
  19         unsigned long size;
  20 
  21         if (!ptr)
  22                 return -EINVAL;
  23         size = LDT_ENTRIES*LDT_ENTRY_SIZE;
  24         if (!address) {
  25                 address = &default_ldt;
  26                 size = sizeof(default_ldt);
  27         }
  28         if (size > bytecount)
  29                 size = bytecount;
  30         error = verify_area(VERIFY_WRITE, ptr, size);
  31         if (error)
  32                 return error;
  33         memcpy_tofs(ptr, address, size);
  34         return size;
  35 }
  36 
  37 static int write_ldt(void * ptr, unsigned long bytecount)
     /*  */
  38 {
  39         struct modify_ldt_ldt_s ldt_info;
  40         unsigned long *lp;
  41         unsigned long base, limit;
  42         int error, i;
  43 
  44         if (bytecount != sizeof(ldt_info))
  45                 return -EINVAL;
  46         error = verify_area(VERIFY_READ, ptr, sizeof(ldt_info));
  47         if (error)
  48                 return error;
  49 
  50         memcpy_fromfs(&ldt_info, ptr, sizeof(ldt_info));
  51 
  52         if (ldt_info.contents == 3 || ldt_info.entry_number >= LDT_ENTRIES)
  53                 return -EINVAL;
  54 
  55         limit = ldt_info.limit;
  56         base = ldt_info.base_addr;
  57         if (ldt_info.limit_in_pages)
  58                 limit *= PAGE_SIZE;
  59 
  60         limit += base;
  61         if (limit < base || limit >= 0xC0000000)
  62                 return -EINVAL;
  63 
  64         if (!current->ldt) {
  65                 for (i=1 ; i<NR_TASKS ; i++) {
  66                         if (task[i] == current) {
  67                                 if (!(current->ldt = (struct desc_struct*) vmalloc(LDT_ENTRIES*LDT_ENTRY_SIZE)))
  68                                         return -ENOMEM;
  69                                 set_ldt_desc(gdt+(i<<1)+FIRST_LDT_ENTRY, current->ldt, LDT_ENTRIES);
  70                                 load_ldt(i);
  71                         }
  72                 }
  73         }
  74         
  75         lp = (unsigned long *) &current->ldt[ldt_info.entry_number];
  76         /* Allow LDTs to be cleared by the user. */
  77         if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
  78                 *lp = 0;
  79                 *(lp+1) = 0;
  80                 return 0;
  81         }
  82         *lp = ((ldt_info.base_addr & 0x0000ffff) << 16) |
  83                   (ldt_info.limit & 0x0ffff);
  84         *(lp+1) = (ldt_info.base_addr & 0xff000000) |
  85                   ((ldt_info.base_addr & 0x00ff0000)>>16) |
  86                   (ldt_info.limit & 0xf0000) |
  87                   (ldt_info.contents << 10) |
  88                   ((ldt_info.read_exec_only ^ 1) << 9) |
  89                   (ldt_info.seg_32bit << 22) |
  90                   (ldt_info.limit_in_pages << 23) |
  91                   ((ldt_info.seg_not_present ^1) << 15) |
  92                   0x7000;
  93         return 0;
  94 }
  95 
  96 asmlinkage int sys_modify_ldt(int func, void *ptr, unsigned long bytecount)
     /*  */
  97 {
  98         if (func == 0)
  99                 return read_ldt(ptr, bytecount);
 100         if (func == 1)
 101                 return write_ldt(ptr, bytecount);
 102         return -ENOSYS;
 103 }

/* */