arch/x86/um/tls_32.c

   1 /*
   2  * Copyright (C) 2005 Paolo 'Blaisorblade' Giarrusso <[email protected]>
   3  * Licensed under the GPL
   4  */
   5
   6 #include <linux/percpu.h>
   7 #include <linux/sched.h>
   8 #include <linux/syscalls.h>
   9 #include <linux/uaccess.h>
  10 #include <asm/ptrace-abi.h>
  11 #include <os.h>
  12 #include <skas.h>
  13 #include <sysdep/tls.h>
  14 #include <asm/desc.h>
  15
  16 /*
  17  * If needed we can detect when it's uninitialized.
  18  *
  19  * These are initialized in an initcall and unchanged thereafter.
  20  */
  21 static int host_supports_tls = -1;
  22 int host_gdt_entry_tls_min;
  23
  24 static int do_set_thread_area(struct user_desc *info)
  25 {
  26         int ret;
  27         u32 cpu;
  28
  29         cpu = get_cpu();
  30         ret = os_set_thread_area(info, userspace_pid[cpu]);
  31         put_cpu();
  32
  33         if (ret)
  34                 printk(KERN_ERR "PTRACE_SET_THREAD_AREA failed, err = %d, "
  35                        "index = %d\n", ret, info->entry_number);
  36
  37         return ret;
  38 }
  39
  40 /*
  41  * sys_get_thread_area: get a yet unused TLS descriptor index.
  42  * XXX: Consider leaving one free slot for glibc usage at first place. This must
  43  * be done here (and by changing GDT_ENTRY_TLS_* macros) and nowhere else.
  44  *
  45  * Also, this must be tested when compiling in SKAS mode with dynamic linking
  46  * and running against NPTL.
  47  */
  48 static int get_free_idx(struct task_struct* task)
  49 {
  50         struct thread_struct *t = &task->thread;
  51         int idx;
  52
  53         for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
  54                 if (!t->arch.tls_array[idx].present)
  55                         return idx + GDT_ENTRY_TLS_MIN;
  56         return -ESRCH;
  57 }
  58
  59 static inline void clear_user_desc(struct user_desc* info)
  60 {
  61         /* Postcondition: LDT_empty(info) returns true. */
  62         memset(info, 0, sizeof(*info));
  63
  64         /*
  65          * Check the LDT_empty or the i386 sys_get_thread_area code - we obtain
  66          * indeed an empty user_desc.
  67          */
  68         info->read_exec_only = 1;
  69         info->seg_not_present = 1;
  70 }
  71
  72 #define O_FORCE 1
  73
  74 static int load_TLS(int flags, struct task_struct *to)
  75 {
  76         int ret = 0;
  77         int idx;
  78
  79         for (idx = GDT_ENTRY_TLS_MIN; idx < GDT_ENTRY_TLS_MAX; idx++) {
  80                 struct uml_tls_struct* curr =
  81                         &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];
  82
  83                 /*
  84                  * Actually, now if it wasn't flushed it gets cleared and
  85                  * flushed to the host, which will clear it.
  86                  */
  87                 if (!curr->present) {
  88                         if (!curr->flushed) {
  89                                 clear_user_desc(&curr->tls);
  90                                 curr->tls.entry_number = idx;
  91                         } else {
  92                                 WARN_ON(!LDT_empty(&curr->tls));
  93                                 continue;
  94                         }
  95                 }
  96
  97                 if (!(flags & O_FORCE) && curr->flushed)
  98                         continue;
  99
 100                 ret = do_set_thread_area(&curr->tls);
 101                 if (ret)
 102                         goto out;
 103
 104                 curr->flushed = 1;
 105         }
 106 out:
 107         return ret;
 108 }
 109
 110 /*
 111  * Verify if we need to do a flush for the new process, i.e. if there are any
 112  * present desc's, only if they haven't been flushed.
 113  */
 114 static inline int needs_TLS_update(struct task_struct *task)
 115 {
 116         int i;
 117         int ret = 0;
 118
 119         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 120                 struct uml_tls_struct* curr =
 121                         &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 122
 123                 /*
 124                  * Can't test curr->present, we may need to clear a descriptor
 125                  * which had a value.
 126                  */
 127                 if (curr->flushed)
 128                         continue;
 129                 ret = 1;
 130                 break;
 131         }
 132         return ret;
 133 }
 134
 135 /*
 136  * On a newly forked process, the TLS descriptors haven't yet been flushed. So
 137  * we mark them as such and the first switch_to will do the job.
 138  */
 139 void clear_flushed_tls(struct task_struct *task)
 140 {
 141         int i;
 142
 143         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 144                 struct uml_tls_struct* curr =
 145                         &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 146
 147                 /*
 148                  * Still correct to do this, if it wasn't present on the host it
 149                  * will remain as flushed as it was.
 150                  */
 151                 if (!curr->present)
 152                         continue;
 153
 154                 curr->flushed = 0;
 155         }
 156 }
 157
 158 /*
 159  * In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
 160  * common host process. So this is needed in SKAS0 too.
 161  *
 162  * However, if each thread had a different host process (and this was discussed
 163  * for SMP support) this won't be needed.
 164  *
 165  * And this will not need be used when (and if) we'll add support to the host
 166  * SKAS patch.
 167  */
 168
 169 int arch_switch_tls(struct task_struct *to)
 170 {
 171         if (!host_supports_tls)
 172                 return 0;
 173
 174         /*
 175          * We have no need whatsoever to switch TLS for kernel threads; beyond
 176          * that, that would also result in us calling os_set_thread_area with
 177          * userspace_pid[cpu] == 0, which gives an error.
 178          */
 179         if (likely(to->mm))
 180                 return load_TLS(O_FORCE, to);
 181
 182         return 0;
 183 }
 184
 185 static int set_tls_entry(struct task_struct* task, struct user_desc *info,
 186                          int idx, int flushed)
 187 {
 188         struct thread_struct *t = &task->thread;
 189
 190         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 191                 return -EINVAL;
 192
 193         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info;
 194         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1;
 195         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed;
 196
 197         return 0;
 198 }
 199
 200 int arch_set_tls(struct task_struct *new, unsigned long tls)
 201 {
 202         struct user_desc info;
 203         int idx, ret = -EFAULT;
 204
 205         if (copy_from_user(&info, (void __user *) tls, sizeof(info)))
 206                 goto out;
 207
 208         ret = -EINVAL;
 209         if (LDT_empty(&info))
 210                 goto out;
 211
 212         idx = info.entry_number;
 213
 214         ret = set_tls_entry(new, &info, idx, 0);
 215 out:
 216         return ret;
 217 }
 218
 219 static int get_tls_entry(struct task_struct *task, struct user_desc *info,
 220                          int idx)
 221 {
 222         struct thread_struct *t = &task->thread;
 223
 224         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 225                 return -EINVAL;
 226
 227         if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present)
 228                 goto clear;
 229
 230         *info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls;
 231
 232 out:
 233         /*
 234          * Temporary debugging check, to make sure that things have been
 235          * flushed. This could be triggered if load_TLS() failed.
 236          */
 237         if (unlikely(task == current &&
 238                      !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) {
 239                 printk(KERN_ERR "get_tls_entry: task with pid %d got here "
 240                                 "without flushed TLS.", current->pid);
 241         }
 242
 243         return 0;
 244 clear:
 245         /*
 246          * When the TLS entry has not been set, the values read to user in the
 247          * tls_array are 0 (because it's cleared at boot, see
 248          * arch/i386/kernel/head.S:cpu_gdt_table). Emulate that.
 249          */
 250         clear_user_desc(info);
 251         info->entry_number = idx;
 252         goto out;
 253 }
 254
 255 SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, user_desc)
 256 {
 257         struct user_desc info;
 258         int idx, ret;
 259
 260         if (!host_supports_tls)
 261                 return -ENOSYS;
 262
 263         if (copy_from_user(&info, user_desc, sizeof(info)))
 264                 return -EFAULT;
 265
 266         idx = info.entry_number;
 267
 268         if (idx == -1) {
 269                 idx = get_free_idx(current);
 270                 if (idx < 0)
 271                         return idx;
 272                 info.entry_number = idx;
 273                 /* Tell the user which slot we chose for him.*/
 274                 if (put_user(idx, &user_desc->entry_number))
 275                         return -EFAULT;
 276         }
 277
 278         ret = do_set_thread_area(&info);
 279         if (ret)
 280                 return ret;
 281         return set_tls_entry(current, &info, idx, 1);
 282 }
 283
 284 /*
 285  * Perform set_thread_area on behalf of the traced child.
 286  * Note: error handling is not done on the deferred load, and this differ from
 287  * i386. However the only possible error are caused by bugs.
 288  */
 289 int ptrace_set_thread_area(struct task_struct *child, int idx,
 290                            struct user_desc __user *user_desc)
 291 {
 292         struct user_desc info;
 293
 294         if (!host_supports_tls)
 295                 return -EIO;
 296
 297         if (copy_from_user(&info, user_desc, sizeof(info)))
 298                 return -EFAULT;
 299
 300         return set_tls_entry(child, &info, idx, 0);
 301 }
 302
 303 SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, user_desc)
 304 {
 305         struct user_desc info;
 306         int idx, ret;
 307
 308         if (!host_supports_tls)
 309                 return -ENOSYS;
 310
 311         if (get_user(idx, &user_desc->entry_number))
 312                 return -EFAULT;
 313
 314         ret = get_tls_entry(current, &info, idx);
 315         if (ret < 0)
 316                 goto out;
 317
 318         if (copy_to_user(user_desc, &info, sizeof(info)))
 319                 ret = -EFAULT;
 320
 321 out:
 322         return ret;
 323 }
 324
 325 /*
 326  * Perform get_thread_area on behalf of the traced child.
 327  */
 328 int ptrace_get_thread_area(struct task_struct *child, int idx,
 329                 struct user_desc __user *user_desc)
 330 {
 331         struct user_desc info;
 332         int ret;
 333
 334         if (!host_supports_tls)
 335                 return -EIO;
 336
 337         ret = get_tls_entry(child, &info, idx);
 338         if (ret < 0)
 339                 goto out;
 340
 341         if (copy_to_user(user_desc, &info, sizeof(info)))
 342                 ret = -EFAULT;
 343 out:
 344         return ret;
 345 }
 346
 347 /*
 348  * This code is really i386-only, but it detects and logs x86_64 GDT indexes
 349  * if a 32-bit UML is running on a 64-bit host.
 350  */
 351 static int __init __setup_host_supports_tls(void)
 352 {
 353         check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
 354         if (host_supports_tls) {
 355                 printk(KERN_INFO "Host TLS support detected\n");
 356                 printk(KERN_INFO "Detected host type: ");
 357                 switch (host_gdt_entry_tls_min) {
 358                 case GDT_ENTRY_TLS_MIN_I386:
 359                         printk(KERN_CONT "i386");
 360                         break;
 361                 case GDT_ENTRY_TLS_MIN_X86_64:
 362                         printk(KERN_CONT "x86_64");
 363                         break;
 364                 }
 365                 printk(KERN_CONT " (GDT indexes %d to %d)\n",
 366                        host_gdt_entry_tls_min,
 367                        host_gdt_entry_tls_min + GDT_ENTRY_TLS_ENTRIES);
 368         } else
 369                 printk(KERN_ERR "  Host TLS support NOT detected! "
 370                                 "TLS support inside UML will not work\n");
 371         return 0;
 372 }
 373
 374 __initcall(__setup_host_supports_tls);