arch/x86/um/ldt.c

   1 /*
   2  * Copyright (C) 2001 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
   3  * Licensed under the GPL
   4  */
   5
   6 #include <linux/mm.h>
   7 #include <linux/sched.h>
   8 #include <linux/slab.h>
   9 #include <linux/uaccess.h>
  10 #include <asm/unistd.h>
  11 #include <os.h>
  12 #include <skas.h>
  13 #include <sysdep/tls.h>
  14
  15 static inline int modify_ldt (int func, void *ptr, unsigned long bytecount)
  16 {
  17         return syscall(__NR_modify_ldt, func, ptr, bytecount);
  18 }
  19
  20 static long write_ldt_entry(struct mm_id *mm_idp, int func,
  21                      struct user_desc *desc, void **addr, int done)
  22 {
  23         long res;
  24         void *stub_addr;
  25         res = syscall_stub_data(mm_idp, (unsigned long *)desc,
  26                                 (sizeof(*desc) + sizeof(long) - 1) &
  27                                     ~(sizeof(long) - 1),
  28                                 addr, &stub_addr);
  29         if (!res) {
  30                 unsigned long args[] = { func,
  31                                          (unsigned long)stub_addr,
  32                                          sizeof(*desc),
  33                                          0, 0, 0 };
  34                 res = run_syscall_stub(mm_idp, __NR_modify_ldt, args,
  35                                        0, addr, done);
  36         }
  37
  38         return res;
  39 }
  40
  41 /*
  42  * In skas mode, we hold our own ldt data in UML.
  43  * Thus, the code implementing sys_modify_ldt_skas
  44  * is very similar to (and mostly stolen from) sys_modify_ldt
  45  * for arch/i386/kernel/ldt.c
  46  * The routines copied and modified in part are:
  47  * - read_ldt
  48  * - read_default_ldt
  49  * - write_ldt
  50  * - sys_modify_ldt_skas
  51  */
  52
  53 static int read_ldt(void __user * ptr, unsigned long bytecount)
  54 {
  55         int i, err = 0;
  56         unsigned long size;
  57         uml_ldt_t *ldt = &current->mm->context.arch.ldt;
  58
  59         if (!ldt->entry_count)
  60                 goto out;
  61         if (bytecount > LDT_ENTRY_SIZE*LDT_ENTRIES)
  62                 bytecount = LDT_ENTRY_SIZE*LDT_ENTRIES;
  63         err = bytecount;
  64
  65         mutex_lock(&ldt->lock);
  66         if (ldt->entry_count <= LDT_DIRECT_ENTRIES) {
  67                 size = LDT_ENTRY_SIZE*LDT_DIRECT_ENTRIES;
  68                 if (size > bytecount)
  69                         size = bytecount;
  70                 if (copy_to_user(ptr, ldt->u.entries, size))
  71                         err = -EFAULT;
  72                 bytecount -= size;
  73                 ptr += size;
  74         }
  75         else {
  76                 for (i=0; i<ldt->entry_count/LDT_ENTRIES_PER_PAGE && bytecount;
  77                      i++) {
  78                         size = PAGE_SIZE;
  79                         if (size > bytecount)
  80                                 size = bytecount;
  81                         if (copy_to_user(ptr, ldt->u.pages[i], size)) {
  82                                 err = -EFAULT;
  83                                 break;
  84                         }
  85                         bytecount -= size;
  86                         ptr += size;
  87                 }
  88         }
  89         mutex_unlock(&ldt->lock);
  90
  91         if (bytecount == 0 || err == -EFAULT)
  92                 goto out;
  93
  94         if (clear_user(ptr, bytecount))
  95                 err = -EFAULT;
  96
  97 out:
  98         return err;
  99 }
 100
 101 static int read_default_ldt(void __user * ptr, unsigned long bytecount)
 102 {
 103         int err;
 104
 105         if (bytecount > 5*LDT_ENTRY_SIZE)
 106                 bytecount = 5*LDT_ENTRY_SIZE;
 107
 108         err = bytecount;
 109         /*
 110          * UML doesn't support lcall7 and lcall27.
 111          * So, we don't really have a default ldt, but emulate
 112          * an empty ldt of common host default ldt size.
 113          */
 114         if (clear_user(ptr, bytecount))
 115                 err = -EFAULT;
 116
 117         return err;
 118 }
 119
 120 static int write_ldt(void __user * ptr, unsigned long bytecount, int func)
 121 {
 122         uml_ldt_t *ldt = &current->mm->context.arch.ldt;
 123         struct mm_id * mm_idp = &current->mm->context.id;
 124         int i, err;
 125         struct user_desc ldt_info;
 126         struct ldt_entry entry0, *ldt_p;
 127         void *addr = NULL;
 128
 129         err = -EINVAL;
 130         if (bytecount != sizeof(ldt_info))
 131                 goto out;
 132         err = -EFAULT;
 133         if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
 134                 goto out;
 135
 136         err = -EINVAL;
 137         if (ldt_info.entry_number >= LDT_ENTRIES)
 138                 goto out;
 139         if (ldt_info.contents == 3) {
 140                 if (func == 1)
 141                         goto out;
 142                 if (ldt_info.seg_not_present == 0)
 143                         goto out;
 144         }
 145
 146         mutex_lock(&ldt->lock);
 147
 148         err = write_ldt_entry(mm_idp, func, &ldt_info, &addr, 1);
 149         if (err)
 150                 goto out_unlock;
 151
 152         if (ldt_info.entry_number >= ldt->entry_count &&
 153             ldt_info.entry_number >= LDT_DIRECT_ENTRIES) {
 154                 for (i=ldt->entry_count/LDT_ENTRIES_PER_PAGE;
 155                      i*LDT_ENTRIES_PER_PAGE <= ldt_info.entry_number;
 156                      i++) {
 157                         if (i == 0)
 158                                 memcpy(&entry0, ldt->u.entries,
 159                                        sizeof(entry0));
 160                         ldt->u.pages[i] = (struct ldt_entry *)
 161                                 __get_free_page(GFP_KERNEL|__GFP_ZERO);
 162                         if (!ldt->u.pages[i]) {
 163                                 err = -ENOMEM;
 164                                 /* Undo the change in host */
 165                                 memset(&ldt_info, 0, sizeof(ldt_info));
 166                                 write_ldt_entry(mm_idp, 1, &ldt_info, &addr, 1);
 167                                 goto out_unlock;
 168                         }
 169                         if (i == 0) {
 170                                 memcpy(ldt->u.pages[0], &entry0,
 171                                        sizeof(entry0));
 172                                 memcpy(ldt->u.pages[0]+1, ldt->u.entries+1,
 173                                        sizeof(entry0)*(LDT_DIRECT_ENTRIES-1));
 174                         }
 175                         ldt->entry_count = (i + 1) * LDT_ENTRIES_PER_PAGE;
 176                 }
 177         }
 178         if (ldt->entry_count <= ldt_info.entry_number)
 179                 ldt->entry_count = ldt_info.entry_number + 1;
 180
 181         if (ldt->entry_count <= LDT_DIRECT_ENTRIES)
 182                 ldt_p = ldt->u.entries + ldt_info.entry_number;
 183         else
 184                 ldt_p = ldt->u.pages[ldt_info.entry_number/LDT_ENTRIES_PER_PAGE] +
 185                         ldt_info.entry_number%LDT_ENTRIES_PER_PAGE;
 186
 187         if (ldt_info.base_addr == 0 && ldt_info.limit == 0 &&
 188            (func == 1 || LDT_empty(&ldt_info))) {
 189                 ldt_p->a = 0;
 190                 ldt_p->b = 0;
 191         }
 192         else{
 193                 if (func == 1)
 194                         ldt_info.useable = 0;
 195                 ldt_p->a = LDT_entry_a(&ldt_info);
 196                 ldt_p->b = LDT_entry_b(&ldt_info);
 197         }
 198         err = 0;
 199
 200 out_unlock:
 201         mutex_unlock(&ldt->lock);
 202 out:
 203         return err;
 204 }
 205
 206 static long do_modify_ldt_skas(int func, void __user *ptr,
 207                                unsigned long bytecount)
 208 {
 209         int ret = -ENOSYS;
 210
 211         switch (func) {
 212                 case 0:
 213                         ret = read_ldt(ptr, bytecount);
 214                         break;
 215                 case 1:
 216                 case 0x11:
 217                         ret = write_ldt(ptr, bytecount, func);
 218                         break;
 219                 case 2:
 220                         ret = read_default_ldt(ptr, bytecount);
 221                         break;
 222         }
 223         return ret;
 224 }
 225
 226 static DEFINE_SPINLOCK(host_ldt_lock);
 227 static short dummy_list[9] = {0, -1};
 228 static short * host_ldt_entries = NULL;
 229
 230 static void ldt_get_host_info(void)
 231 {
 232         long ret;
 233         struct ldt_entry * ldt;
 234         short *tmp;
 235         int i, size, k, order;
 236
 237         spin_lock(&host_ldt_lock);
 238
 239         if (host_ldt_entries != NULL) {
 240                 spin_unlock(&host_ldt_lock);
 241                 return;
 242         }
 243         host_ldt_entries = dummy_list+1;
 244
 245         spin_unlock(&host_ldt_lock);
 246
 247         for (i = LDT_PAGES_MAX-1, order=0; i; i>>=1, order++)
 248                 ;
 249
 250         ldt = (struct ldt_entry *)
 251               __get_free_pages(GFP_KERNEL|__GFP_ZERO, order);
 252         if (ldt == NULL) {
 253                 printk(KERN_ERR "ldt_get_host_info: couldn't allocate buffer "
 254                        "for host ldt\n");
 255                 return;
 256         }
 257
 258         ret = modify_ldt(0, ldt, (1<<order)*PAGE_SIZE);
 259         if (ret < 0) {
 260                 printk(KERN_ERR "ldt_get_host_info: couldn't read host ldt\n");
 261                 goto out_free;
 262         }
 263         if (ret == 0) {
 264                 /* default_ldt is active, simply write an empty entry 0 */
 265                 host_ldt_entries = dummy_list;
 266                 goto out_free;
 267         }
 268
 269         for (i=0, size=0; i<ret/LDT_ENTRY_SIZE; i++) {
 270                 if (ldt[i].a != 0 || ldt[i].b != 0)
 271                         size++;
 272         }
 273
 274         if (size < ARRAY_SIZE(dummy_list))
 275                 host_ldt_entries = dummy_list;
 276         else {
 277                 size = (size + 1) * sizeof(dummy_list[0]);
 278                 tmp = kmalloc(size, GFP_KERNEL);
 279                 if (tmp == NULL) {
 280                         printk(KERN_ERR "ldt_get_host_info: couldn't allocate "
 281                                "host ldt list\n");
 282                         goto out_free;
 283                 }
 284                 host_ldt_entries = tmp;
 285         }
 286
 287         for (i=0, k=0; i<ret/LDT_ENTRY_SIZE; i++) {
 288                 if (ldt[i].a != 0 || ldt[i].b != 0)
 289                         host_ldt_entries[k++] = i;
 290         }
 291         host_ldt_entries[k] = -1;
 292
 293 out_free:
 294         free_pages((unsigned long)ldt, order);
 295 }
 296
 297 long init_new_ldt(struct mm_context *new_mm, struct mm_context *from_mm)
 298 {
 299         struct user_desc desc;
 300         short * num_p;
 301         int i;
 302         long page, err=0;
 303         void *addr = NULL;
 304
 305
 306         mutex_init(&new_mm->arch.ldt.lock);
 307
 308         if (!from_mm) {
 309                 memset(&desc, 0, sizeof(desc));
 310                 /*
 311                  * Now we try to retrieve info about the ldt, we
 312                  * inherited from the host. All ldt-entries found
 313                  * will be reset in the following loop
 314                  */
 315                 ldt_get_host_info();
 316                 for (num_p=host_ldt_entries; *num_p != -1; num_p++) {
 317                         desc.entry_number = *num_p;
 318                         err = write_ldt_entry(&new_mm->id, 1, &desc,
 319                                               &addr, *(num_p + 1) == -1);
 320                         if (err)
 321                                 break;
 322                 }
 323                 new_mm->arch.ldt.entry_count = 0;
 324
 325                 goto out;
 326         }
 327
 328         /*
 329          * Our local LDT is used to supply the data for
 330          * modify_ldt(READLDT), if PTRACE_LDT isn't available,
 331          * i.e., we have to use the stub for modify_ldt, which
 332          * can't handle the big read buffer of up to 64kB.
 333          */
 334         mutex_lock(&from_mm->arch.ldt.lock);
 335         if (from_mm->arch.ldt.entry_count <= LDT_DIRECT_ENTRIES)
 336                 memcpy(new_mm->arch.ldt.u.entries, from_mm->arch.ldt.u.entries,
 337                        sizeof(new_mm->arch.ldt.u.entries));
 338         else {
 339                 i = from_mm->arch.ldt.entry_count / LDT_ENTRIES_PER_PAGE;
 340                 while (i-->0) {
 341                         page = __get_free_page(GFP_KERNEL|__GFP_ZERO);
 342                         if (!page) {
 343                                 err = -ENOMEM;
 344                                 break;
 345                         }
 346                         new_mm->arch.ldt.u.pages[i] =
 347                                 (struct ldt_entry *) page;
 348                         memcpy(new_mm->arch.ldt.u.pages[i],
 349                                from_mm->arch.ldt.u.pages[i], PAGE_SIZE);
 350                 }
 351         }
 352         new_mm->arch.ldt.entry_count = from_mm->arch.ldt.entry_count;
 353         mutex_unlock(&from_mm->arch.ldt.lock);
 354
 355     out:
 356         return err;
 357 }
 358
 359
 360 void free_ldt(struct mm_context *mm)
 361 {
 362         int i;
 363
 364         if (mm->arch.ldt.entry_count > LDT_DIRECT_ENTRIES) {
 365                 i = mm->arch.ldt.entry_count / LDT_ENTRIES_PER_PAGE;
 366                 while (i-- > 0)
 367                         free_page((long) mm->arch.ldt.u.pages[i]);
 368         }
 369         mm->arch.ldt.entry_count = 0;
 370 }
 371
 372 int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount)
 373 {
 374         return do_modify_ldt_skas(func, ptr, bytecount);
 375 }