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