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/syscalls.h>
  10 #include <linux/uaccess.h>
  11 #include <asm/unistd.h>
  12 #include <os.h>
  13 #include <skas.h>
  14 #include <sysdep/tls.h>
  15
  16 static inline int modify_ldt (int func, void *ptr, unsigned long bytecount)
  17 {
  18         return syscall(__NR_modify_ldt, func, ptr, bytecount);
  19 }
  20
  21 static long write_ldt_entry(struct mm_id *mm_idp, int func,
  22                      struct user_desc *desc, void **addr, int done)
  23 {
  24         long res;
  25         void *stub_addr;
  26
  27         BUILD_BUG_ON(sizeof(*desc) % sizeof(long));
  28
  29         res = syscall_stub_data(mm_idp, (unsigned long *)desc,
  30                                 sizeof(*desc) / sizeof(long),
  31                                 addr, &stub_addr);
  32         if (!res) {
  33                 unsigned long args[] = { func,
  34                                          (unsigned long)stub_addr,
  35                                          sizeof(*desc),
  36                                          0, 0, 0 };
  37                 res = run_syscall_stub(mm_idp, __NR_modify_ldt, args,
  38                                        0, addr, done);
  39         }
  40
  41         return res;
  42 }
  43
  44 /*
  45  * In skas mode, we hold our own ldt data in UML.
  46  * Thus, the code implementing sys_modify_ldt_skas
  47  * is very similar to (and mostly stolen from) sys_modify_ldt
  48  * for arch/i386/kernel/ldt.c
  49  * The routines copied and modified in part are:
  50  * - read_ldt
  51  * - read_default_ldt
  52  * - write_ldt
  53  * - sys_modify_ldt_skas
  54  */
  55
  56 static int read_ldt(void __user * ptr, unsigned long bytecount)
  57 {
  58         int i, err = 0;
  59         unsigned long size;
  60         uml_ldt_t *ldt = &current->mm->context.arch.ldt;
  61
  62         if (!ldt->entry_count)
  63                 goto out;
  64         if (bytecount > LDT_ENTRY_SIZE*LDT_ENTRIES)
  65                 bytecount = LDT_ENTRY_SIZE*LDT_ENTRIES;
  66         err = bytecount;
  67
  68         mutex_lock(&ldt->lock);
  69         if (ldt->entry_count <= LDT_DIRECT_ENTRIES) {
  70                 size = LDT_ENTRY_SIZE*LDT_DIRECT_ENTRIES;
  71                 if (size > bytecount)
  72                         size = bytecount;
  73                 if (copy_to_user(ptr, ldt->u.entries, size))
  74                         err = -EFAULT;
  75                 bytecount -= size;
  76                 ptr += size;
  77         }
  78         else {
  79                 for (i=0; i<ldt->entry_count/LDT_ENTRIES_PER_PAGE && bytecount;
  80                      i++) {
  81                         size = PAGE_SIZE;
  82                         if (size > bytecount)
  83                                 size = bytecount;
  84                         if (copy_to_user(ptr, ldt->u.pages[i], size)) {
  85                                 err = -EFAULT;
  86                                 break;
  87                         }
  88                         bytecount -= size;
  89                         ptr += size;
  90                 }
  91         }
  92         mutex_unlock(&ldt->lock);
  93
  94         if (bytecount == 0 || err == -EFAULT)
  95                 goto out;
  96
  97         if (clear_user(ptr, bytecount))
  98                 err = -EFAULT;
  99
 100 out:
 101         return err;
 102 }
 103
 104 static int read_default_ldt(void __user * ptr, unsigned long bytecount)
 105 {
 106         int err;
 107
 108         if (bytecount > 5*LDT_ENTRY_SIZE)
 109                 bytecount = 5*LDT_ENTRY_SIZE;
 110
 111         err = bytecount;
 112         /*
 113          * UML doesn't support lcall7 and lcall27.
 114          * So, we don't really have a default ldt, but emulate
 115          * an empty ldt of common host default ldt size.
 116          */
 117         if (clear_user(ptr, bytecount))
 118                 err = -EFAULT;
 119
 120         return err;
 121 }
 122
 123 static int write_ldt(void __user * ptr, unsigned long bytecount, int func)
 124 {
 125         uml_ldt_t *ldt = &current->mm->context.arch.ldt;
 126         struct mm_id * mm_idp = &current->mm->context.id;
 127         int i, err;
 128         struct user_desc ldt_info;
 129         struct ldt_entry entry0, *ldt_p;
 130         void *addr = NULL;
 131
 132         err = -EINVAL;
 133         if (bytecount != sizeof(ldt_info))
 134                 goto out;
 135         err = -EFAULT;
 136         if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
 137                 goto out;
 138
 139         err = -EINVAL;
 140         if (ldt_info.entry_number >= LDT_ENTRIES)
 141                 goto out;
 142         if (ldt_info.contents == 3) {
 143                 if (func == 1)
 144                         goto out;
 145                 if (ldt_info.seg_not_present == 0)
 146                         goto out;
 147         }
 148
 149         mutex_lock(&ldt->lock);
 150
 151         err = write_ldt_entry(mm_idp, func, &ldt_info, &addr, 1);
 152         if (err)
 153                 goto out_unlock;
 154
 155         if (ldt_info.entry_number >= ldt->entry_count &&
 156             ldt_info.entry_number >= LDT_DIRECT_ENTRIES) {
 157                 for (i=ldt->entry_count/LDT_ENTRIES_PER_PAGE;
 158                      i*LDT_ENTRIES_PER_PAGE <= ldt_info.entry_number;
 159                      i++) {
 160                         if (i == 0)
 161                                 memcpy(&entry0, ldt->u.entries,
 162                                        sizeof(entry0));
 163                         ldt->u.pages[i] = (struct ldt_entry *)
 164                                 __get_free_page(GFP_KERNEL|__GFP_ZERO);
 165                         if (!ldt->u.pages[i]) {
 166                                 err = -ENOMEM;
 167                                 /* Undo the change in host */
 168                                 memset(&ldt_info, 0, sizeof(ldt_info));
 169                                 write_ldt_entry(mm_idp, 1, &ldt_info, &addr, 1);
 170                                 goto out_unlock;
 171                         }
 172                         if (i == 0) {
 173                                 memcpy(ldt->u.pages[0], &entry0,
 174                                        sizeof(entry0));
 175                                 memcpy(ldt->u.pages[0]+1, ldt->u.entries+1,
 176                                        sizeof(entry0)*(LDT_DIRECT_ENTRIES-1));
 177                         }
 178                         ldt->entry_count = (i + 1) * LDT_ENTRIES_PER_PAGE;
 179                 }
 180         }
 181         if (ldt->entry_count <= ldt_info.entry_number)
 182                 ldt->entry_count = ldt_info.entry_number + 1;
 183
 184         if (ldt->entry_count <= LDT_DIRECT_ENTRIES)
 185                 ldt_p = ldt->u.entries + ldt_info.entry_number;
 186         else
 187                 ldt_p = ldt->u.pages[ldt_info.entry_number/LDT_ENTRIES_PER_PAGE] +
 188                         ldt_info.entry_number%LDT_ENTRIES_PER_PAGE;
 189
 190         if (ldt_info.base_addr == 0 && ldt_info.limit == 0 &&
 191            (func == 1 || LDT_empty(&ldt_info))) {
 192                 ldt_p->a = 0;
 193                 ldt_p->b = 0;
 194         }
 195         else{
 196                 if (func == 1)
 197                         ldt_info.useable = 0;
 198                 ldt_p->a = LDT_entry_a(&ldt_info);
 199                 ldt_p->b = LDT_entry_b(&ldt_info);
 200         }
 201         err = 0;
 202
 203 out_unlock:
 204         mutex_unlock(&ldt->lock);
 205 out:
 206         return err;
 207 }
 208
 209 static long do_modify_ldt_skas(int func, void __user *ptr,
 210                                unsigned long bytecount)
 211 {
 212         int ret = -ENOSYS;
 213
 214         switch (func) {
 215                 case 0:
 216                         ret = read_ldt(ptr, bytecount);
 217                         break;
 218                 case 1:
 219                 case 0x11:
 220                         ret = write_ldt(ptr, bytecount, func);
 221                         break;
 222                 case 2:
 223                         ret = read_default_ldt(ptr, bytecount);
 224                         break;
 225         }
 226         return ret;
 227 }
 228
 229 static DEFINE_SPINLOCK(host_ldt_lock);
 230 static short dummy_list[9] = {0, -1};
 231 static short * host_ldt_entries = NULL;
 232
 233 static void ldt_get_host_info(void)
 234 {
 235         long ret;
 236         struct ldt_entry * ldt;
 237         short *tmp;
 238         int i, size, k, order;
 239
 240         spin_lock(&host_ldt_lock);
 241
 242         if (host_ldt_entries != NULL) {
 243                 spin_unlock(&host_ldt_lock);
 244                 return;
 245         }
 246         host_ldt_entries = dummy_list+1;
 247
 248         spin_unlock(&host_ldt_lock);
 249
 250         for (i = LDT_PAGES_MAX-1, order=0; i; i>>=1, order++)
 251                 ;
 252
 253         ldt = (struct ldt_entry *)
 254               __get_free_pages(GFP_KERNEL|__GFP_ZERO, order);
 255         if (ldt == NULL) {
 256                 printk(KERN_ERR "ldt_get_host_info: couldn't allocate buffer "
 257                        "for host ldt\n");
 258                 return;
 259         }
 260
 261         ret = modify_ldt(0, ldt, (1<<order)*PAGE_SIZE);
 262         if (ret < 0) {
 263                 printk(KERN_ERR "ldt_get_host_info: couldn't read host ldt\n");
 264                 goto out_free;
 265         }
 266         if (ret == 0) {
 267                 /* default_ldt is active, simply write an empty entry 0 */
 268                 host_ldt_entries = dummy_list;
 269                 goto out_free;
 270         }
 271
 272         for (i=0, size=0; i<ret/LDT_ENTRY_SIZE; i++) {
 273                 if (ldt[i].a != 0 || ldt[i].b != 0)
 274                         size++;
 275         }
 276
 277         if (size < ARRAY_SIZE(dummy_list))
 278                 host_ldt_entries = dummy_list;
 279         else {
 280                 size = (size + 1) * sizeof(dummy_list[0]);
 281                 tmp = kmalloc(size, GFP_KERNEL);
 282                 if (tmp == NULL) {
 283                         printk(KERN_ERR "ldt_get_host_info: couldn't allocate "
 284                                "host ldt list\n");
 285                         goto out_free;
 286                 }
 287                 host_ldt_entries = tmp;
 288         }
 289
 290         for (i=0, k=0; i<ret/LDT_ENTRY_SIZE; i++) {
 291                 if (ldt[i].a != 0 || ldt[i].b != 0)
 292                         host_ldt_entries[k++] = i;
 293         }
 294         host_ldt_entries[k] = -1;
 295
 296 out_free:
 297         free_pages((unsigned long)ldt, order);
 298 }
 299
 300 long init_new_ldt(struct mm_context *new_mm, struct mm_context *from_mm)
 301 {
 302         struct user_desc desc;
 303         short * num_p;
 304         int i;
 305         long page, err=0;
 306         void *addr = NULL;
 307
 308
 309         mutex_init(&new_mm->arch.ldt.lock);
 310
 311         if (!from_mm) {
 312                 memset(&desc, 0, sizeof(desc));
 313                 /*
 314                  * Now we try to retrieve info about the ldt, we
 315                  * inherited from the host. All ldt-entries found
 316                  * will be reset in the following loop
 317                  */
 318                 ldt_get_host_info();
 319                 for (num_p=host_ldt_entries; *num_p != -1; num_p++) {
 320                         desc.entry_number = *num_p;
 321                         err = write_ldt_entry(&new_mm->id, 1, &desc,
 322                                               &addr, *(num_p + 1) == -1);
 323                         if (err)
 324                                 break;
 325                 }
 326                 new_mm->arch.ldt.entry_count = 0;
 327
 328                 goto out;
 329         }
 330
 331         /*
 332          * Our local LDT is used to supply the data for
 333          * modify_ldt(READLDT), if PTRACE_LDT isn't available,
 334          * i.e., we have to use the stub for modify_ldt, which
 335          * can't handle the big read buffer of up to 64kB.
 336          */
 337         mutex_lock(&from_mm->arch.ldt.lock);
 338         if (from_mm->arch.ldt.entry_count <= LDT_DIRECT_ENTRIES)
 339                 memcpy(new_mm->arch.ldt.u.entries, from_mm->arch.ldt.u.entries,
 340                        sizeof(new_mm->arch.ldt.u.entries));
 341         else {
 342                 i = from_mm->arch.ldt.entry_count / LDT_ENTRIES_PER_PAGE;
 343                 while (i-->0) {
 344                         page = __get_free_page(GFP_KERNEL|__GFP_ZERO);
 345                         if (!page) {
 346                                 err = -ENOMEM;
 347                                 break;
 348                         }
 349                         new_mm->arch.ldt.u.pages[i] =
 350                                 (struct ldt_entry *) page;
 351                         memcpy(new_mm->arch.ldt.u.pages[i],
 352                                from_mm->arch.ldt.u.pages[i], PAGE_SIZE);
 353                 }
 354         }
 355         new_mm->arch.ldt.entry_count = from_mm->arch.ldt.entry_count;
 356         mutex_unlock(&from_mm->arch.ldt.lock);
 357
 358     out:
 359         return err;
 360 }
 361
 362
 363 void free_ldt(struct mm_context *mm)
 364 {
 365         int i;
 366
 367         if (mm->arch.ldt.entry_count > LDT_DIRECT_ENTRIES) {
 368                 i = mm->arch.ldt.entry_count / LDT_ENTRIES_PER_PAGE;
 369                 while (i-- > 0)
 370                         free_page((long) mm->arch.ldt.u.pages[i]);
 371         }
 372         mm->arch.ldt.entry_count = 0;
 373 }
 374
 375 SYSCALL_DEFINE3(modify_ldt, int , func , void __user * , ptr ,
 376                 unsigned long , bytecount)
 377 {
 378         /* See non-um modify_ldt() for why we do this cast */
 379         return (unsigned int)do_modify_ldt_skas(func, ptr, bytecount);
 380 }