service_runtime/modify_ldt.c

   1 /*
   2  * Copyright 2008, Google Inc.
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met:
   8  *
   9  *     * Redistributions of source code must retain the above copyright
  10  * notice, this list of conditions and the following disclaimer.
  11  *     * Redistributions in binary form must reproduce the above
  12  * copyright notice, this list of conditions and the following disclaimer
  13  * in the documentation and/or other materials provided with the
  14  * distribution.
  15  *     * Neither the name of Google Inc. nor the names of its
  16  * contributors may be used to endorse or promote products derived from
  17  * this software without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  20  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  21  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  22  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  23  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  24  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  25  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  26  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  27  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  28  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  29  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  30  */
  31
  32 /*
  33  * Test code for exercising the modify_ldt function.
  34  */
  35 #include <stdio.h>
  36 #include <stdint.h>
  37 #include <errno.h>
  38 #include <stdlib.h>
  39 #include <unistd.h>
  40 #include <sys/types.h>
  41 #include <asm/ldt.h>
  42
  43 void  hex_dump(uint8_t    *buf,
  44                int        size)
  45 {
  46   int i;
  47   int sep;
  48   for (i = 0; i < size; ++i) {
  49     sep = ' ';
  50     if (!(i & 0x3)) sep = '\t';
  51     if (!(i & 0xf)) sep = '\n';
  52     printf("%c%02x", sep, buf[i]);
  53   }
  54   printf("\n");
  55 }
  56
  57 extern int  modify_ldt(int, void *, unsigned long);
  58 extern int  etext;
  59
  60 unsigned short  getds(void)
  61 {
  62   unsigned short  ds;
  63
  64   asm("mov %%ds, %0"
  65       : "=r" (ds)
  66       : );
  67
  68   return ds;
  69 }
  70
  71 void  setds(unsigned short    ds)
  72 {
  73   asm("movw %0, %%ds"
  74       : : "r" (ds));
  75 }
  76
  77 void  print_segreg(unsigned short    seg)
  78 {
  79   printf("%02x: index %d (%x), %s, rpl %d\n",
  80          seg,
  81          (seg >> 3),
  82          (seg >> 3),
  83          (seg & 0x4) ? "LDT" : "GDT",
  84          (seg & 0x3));
  85 }
  86
  87 void  print_segdesc(uint8_t       *ptr)
  88 {
  89   uint32_t    base_addr;
  90   uint32_t    seg_limit;  /* 20 bits */
  91   uint32_t    v;
  92   int         g, db, p, dpl, s, type;
  93
  94   v = *ptr++;
  95   seg_limit = v;
  96   v = *ptr++;
  97   seg_limit |= (v << 8);
  98   v = *ptr++;
  99   base_addr = v;
 100   v = *ptr++;
 101   base_addr |= (v << 8);
 102   v = *ptr++;
 103   base_addr |= (v << 16);
 104   v = *ptr++;
 105   type = v & 0xf;
 106   s = (v >> 4) & 1;
 107   dpl = (v >> 5) & 0x3;
 108   p = (v>>7) & 1;
 109   v = *ptr++;
 110   seg_limit |= (v & 0xf) << 16;
 111   db = (v >> 6) & 1;
 112   g = (v >> 7) & 1;
 113   v = *ptr++;
 114   base_addr |= (v << 24);
 115
 116   printf("base addr: 0x%08x\n", base_addr);
 117   printf("limit:     0x%05x\n", seg_limit);
 118   printf("g %d, db %d, p %d, dpl %x, s %d, type %x\n",
 119          g, db, p, dpl, s, type);
 120 }
 121
 122 int main(int    ac,
 123          char   **av)
 124 {
 125   int               opt;
 126
 127   intptr_t          base_addr = 0; // 0x08048000;
 128   int               num_pages = -1;
 129   intptr_t          addr;
 130   uint8_t           buf[LDT_ENTRIES * LDT_ENTRY_SIZE];
 131   int               actual;
 132   struct user_desc  ud;
 133   uint16_t          ds, nds;
 134   char const        *fmt = "mem[0x%08x] = %02x\n";
 135   char              ch;
 136
 137   while ((opt = getopt(ac, av, "a:b:p:")) != -1) {
 138     switch (opt) {
 139       case 'a':
 140         addr = strtoul(optarg, (char **) 0, 0);
 141         break;
 142       case 'b':
 143         base_addr = strtoul(optarg, (char **) 0, 0);
 144         break;
 145       case 'p':
 146         num_pages = strtoul(optarg, (char **) 0, 0);
 147         break;
 148       default:
 149         fprintf(stderr, "Usage: modify_ldt [-a addr-to-read] [-b base_addr] [-p num_pages]\n");
 150         return 1;
 151     }
 152   }
 153
 154   printf("main:            0x%08x\n", (intptr_t) main);
 155   printf("etext:           0x%08x\n", (intptr_t) &etext);
 156   printf("aprox stack loc: 0x%08x\n", (intptr_t) &opt);
 157   printf("fmt loc:         0x%08x\n", (intptr_t) fmt);
 158
 159   printf("ds = %x\n", getds());
 160   print_segreg(getds());
 161
 162   actual = modify_ldt(0, buf, sizeof buf);
 163   if (-1 == actual) {
 164     perror("modify_ldt");
 165     exit(1);
 166   }
 167   printf("LDT size %d (0x%x)\n", actual, actual);
 168   hex_dump(buf, actual);
 169
 170   printf("ds = %x\n", getds());
 171   print_segreg(getds());
 172
 173   ud.entry_number = 0;
 174   ud.base_addr = base_addr;
 175   if (-1 == num_pages) {
 176     num_pages = ((1 << 20)-1) - base_addr / (4 << 10);
 177   }
 178
 179   if (num_pages != (0xfffff & num_pages)) {
 180     fprintf(stderr, "WARNING: num_pages overflows\n");
 181   }
 182   ud.limit = num_pages;
 183   ud.seg_32bit = 1;
 184   ud.contents = MODIFY_LDT_CONTENTS_DATA;
 185   ud.read_exec_only = 0;
 186   ud.limit_in_pages = 1;
 187   ud.seg_not_present = 0;
 188   ud.useable = 1;
 189
 190   printf("base addr: 0x%08x\n", base_addr);
 191   printf("num pages: 0x%08x\n", num_pages);
 192   printf("end addr:  0x%08x\n", base_addr + ((num_pages+1) << 12));
 193
 194   actual = modify_ldt(1, &ud, sizeof ud);
 195   printf("returned %d\n", actual);
 196
 197   ds = getds();
 198   setds((ud.entry_number << 3) | (1<<2) | (0x3));
 199   nds = getds();
 200
 201   if (0 != addr) {
 202     unsigned char   *p = (unsigned char *) addr;
 203
 204     ch = *p;
 205   }
 206
 207   setds(ds);
 208
 209   if (0 != addr) {
 210     printf(fmt, addr, ch);
 211   }
 212
 213   printf("while ds modified:\n");
 214   print_segreg(nds);
 215
 216   actual = modify_ldt(0, buf, sizeof buf);
 217   if (-1 == actual) {
 218     perror("modify_ldt");
 219     exit(1);
 220   }
 221   printf("LDT size %d (0x%x)\n", actual, actual);
 222   print_segdesc(buf);
 223   hex_dump(buf, 10 * LDT_ENTRY_SIZE);
 224
 225   return 0;
 226 }