arch/um/sys-i386/tls.c

   1 /*
   2  * Copyright (C) 2005 Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
   3  * Licensed under the GPL
   4  */
   5
   6 #include "linux/kernel.h"
   7 #include "linux/sched.h"
   8 #include "linux/slab.h"
   9 #include "linux/types.h"
  10 #include "asm/uaccess.h"
  11 #include "asm/ptrace.h"
  12 #include "asm/segment.h"
  13 #include "asm/smp.h"
  14 #include "asm/desc.h"
  15 #include "choose-mode.h"
  16 #include "kern.h"
  17 #include "kern_util.h"
  18 #include "mode_kern.h"
  19 #include "os.h"
  20 #include "mode.h"
  21
  22 #ifdef CONFIG_MODE_SKAS
  23 #include "skas.h"
  24 #endif
  25
  26 /*
  27  * If needed we can detect when it's uninitialized.
  28  *
  29  * These are initialized in an initcall and unchanged thereafter.
  30  */
  31 static int host_supports_tls = -1;
  32 int host_gdt_entry_tls_min;
  33
  34 #ifdef CONFIG_MODE_SKAS
  35 int do_set_thread_area_skas(struct user_desc *info)
  36 {
  37         int ret;
  38         u32 cpu;
  39
  40         cpu = get_cpu();
  41         ret = os_set_thread_area(info, userspace_pid[cpu]);
  42         put_cpu();
  43         return ret;
  44 }
  45
  46 int do_get_thread_area_skas(struct user_desc *info)
  47 {
  48         int ret;
  49         u32 cpu;
  50
  51         cpu = get_cpu();
  52         ret = os_get_thread_area(info, userspace_pid[cpu]);
  53         put_cpu();
  54         return ret;
  55 }
  56 #endif
  57
  58 /*
  59  * sys_get_thread_area: get a yet unused TLS descriptor index.
  60  * XXX: Consider leaving one free slot for glibc usage at first place. This must
  61  * be done here (and by changing GDT_ENTRY_TLS_* macros) and nowhere else.
  62  *
  63  * Also, this must be tested when compiling in SKAS mode with dinamic linking
  64  * and running against NPTL.
  65  */
  66 static int get_free_idx(struct task_struct* task)
  67 {
  68         struct thread_struct *t = &task->thread;
  69         int idx;
  70
  71         if (!t->arch.tls_array)
  72                 return GDT_ENTRY_TLS_MIN;
  73
  74         for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
  75                 if (!t->arch.tls_array[idx].present)
  76                         return idx + GDT_ENTRY_TLS_MIN;
  77         return -ESRCH;
  78 }
  79
  80 static inline void clear_user_desc(struct user_desc* info)
  81 {
  82         /* Postcondition: LDT_empty(info) returns true. */
  83         memset(info, 0, sizeof(*info));
  84
  85         /* Check the LDT_empty or the i386 sys_get_thread_area code - we obtain
  86          * indeed an empty user_desc.
  87          */
  88         info->read_exec_only = 1;
  89         info->seg_not_present = 1;
  90 }
  91
  92 #define O_FORCE 1
  93
  94 static int load_TLS(int flags, struct task_struct *to)
  95 {
  96         int ret = 0;
  97         int idx;
  98
  99         for (idx = GDT_ENTRY_TLS_MIN; idx < GDT_ENTRY_TLS_MAX; idx++) {
 100                 struct uml_tls_struct* curr = &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];
 101
 102                 /* Actually, now if it wasn't flushed it gets cleared and
 103                  * flushed to the host, which will clear it.*/
 104                 if (!curr->present) {
 105                         if (!curr->flushed) {
 106                                 clear_user_desc(&curr->tls);
 107                                 curr->tls.entry_number = idx;
 108                         } else {
 109                                 WARN_ON(!LDT_empty(&curr->tls));
 110                                 continue;
 111                         }
 112                 }
 113
 114                 if (!(flags & O_FORCE) && curr->flushed)
 115                         continue;
 116
 117                 ret = do_set_thread_area(&curr->tls);
 118                 if (ret)
 119                         goto out;
 120
 121                 curr->flushed = 1;
 122         }
 123 out:
 124         return ret;
 125 }
 126
 127 /* Verify if we need to do a flush for the new process, i.e. if there are any
 128  * present desc's, only if they haven't been flushed.
 129  */
 130 static inline int needs_TLS_update(struct task_struct *task)
 131 {
 132         int i;
 133         int ret = 0;
 134
 135         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 136                 struct uml_tls_struct* curr = &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 137
 138                 /* Can't test curr->present, we may need to clear a descriptor
 139                  * which had a value. */
 140                 if (curr->flushed)
 141                         continue;
 142                 ret = 1;
 143                 break;
 144         }
 145         return ret;
 146 }
 147
 148 /* On a newly forked process, the TLS descriptors haven't yet been flushed. So
 149  * we mark them as such and the first switch_to will do the job.
 150  */
 151 void clear_flushed_tls(struct task_struct *task)
 152 {
 153         int i;
 154
 155         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 156                 struct uml_tls_struct* curr = &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 157
 158                 /* Still correct to do this, if it wasn't present on the host it
 159                  * will remain as flushed as it was. */
 160                 if (!curr->present)
 161                         continue;
 162
 163                 curr->flushed = 0;
 164         }
 165 }
 166
 167 /* In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
 168  * common host process. So this is needed in SKAS0 too.
 169  *
 170  * However, if each thread had a different host process (and this was discussed
 171  * for SMP support) this won't be needed.
 172  *
 173  * And this will not need be used when (and if) we'll add support to the host
 174  * SKAS patch. */
 175
 176 int arch_switch_tls_skas(struct task_struct *from, struct task_struct *to)
 177 {
 178         if (!host_supports_tls)
 179                 return 0;
 180
 181         /* We have no need whatsoever to switch TLS for kernel threads; beyond
 182          * that, that would also result in us calling os_set_thread_area with
 183          * userspace_pid[cpu] == 0, which gives an error. */
 184         if (likely(to->mm))
 185                 return load_TLS(O_FORCE, to);
 186
 187         return 0;
 188 }
 189
 190 int arch_switch_tls_tt(struct task_struct *from, struct task_struct *to)
 191 {
 192         if (!host_supports_tls)
 193                 return 0;
 194
 195         if (needs_TLS_update(to))
 196                 return load_TLS(0, to);
 197
 198         return 0;
 199 }
 200
 201 static int set_tls_entry(struct task_struct* task, struct user_desc *info,
 202                          int idx, int flushed)
 203 {
 204         struct thread_struct *t = &task->thread;
 205
 206         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 207                 return -EINVAL;
 208
 209         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info;
 210         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1;
 211         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed;
 212
 213         return 0;
 214 }
 215
 216 int arch_copy_tls(struct task_struct *new)
 217 {
 218         struct user_desc info;
 219         int idx, ret = -EFAULT;
 220
 221         if (copy_from_user(&info,
 222                            (void __user *) UPT_ESI(&new->thread.regs.regs),
 223                            sizeof(info)))
 224                 goto out;
 225
 226         ret = -EINVAL;
 227         if (LDT_empty(&info))
 228                 goto out;
 229
 230         idx = info.entry_number;
 231
 232         ret = set_tls_entry(new, &info, idx, 0);
 233 out:
 234         return ret;
 235 }
 236
 237 /* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */
 238 static int get_tls_entry(struct task_struct* task, struct user_desc *info, int idx)
 239 {
 240         struct thread_struct *t = &task->thread;
 241
 242         if (!t->arch.tls_array)
 243                 goto clear;
 244
 245         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 246                 return -EINVAL;
 247
 248         if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present)
 249                 goto clear;
 250
 251         *info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls;
 252
 253 out:
 254         /* Temporary debugging check, to make sure that things have been
 255          * flushed. This could be triggered if load_TLS() failed.
 256          */
 257         if (unlikely(task == current && !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) {
 258                 printk(KERN_ERR "get_tls_entry: task with pid %d got here "
 259                                 "without flushed TLS.", current->pid);
 260         }
 261
 262         return 0;
 263 clear:
 264         /* When the TLS entry has not been set, the values read to user in the
 265          * tls_array are 0 (because it's cleared at boot, see
 266          * arch/i386/kernel/head.S:cpu_gdt_table). Emulate that.
 267          */
 268         clear_user_desc(info);
 269         info->entry_number = idx;
 270         goto out;
 271 }
 272
 273 asmlinkage int sys_set_thread_area(struct user_desc __user *user_desc)
 274 {
 275         struct user_desc info;
 276         int idx, ret;
 277
 278         if (!host_supports_tls)
 279                 return -ENOSYS;
 280
 281         if (copy_from_user(&info, user_desc, sizeof(info)))
 282                 return -EFAULT;
 283
 284         idx = info.entry_number;
 285
 286         if (idx == -1) {
 287                 idx = get_free_idx(current);
 288                 if (idx < 0)
 289                         return idx;
 290                 info.entry_number = idx;
 291                 /* Tell the user which slot we chose for him.*/
 292                 if (put_user(idx, &user_desc->entry_number))
 293                         return -EFAULT;
 294         }
 295
 296         ret = CHOOSE_MODE_PROC(do_set_thread_area_tt, do_set_thread_area_skas, &info);
 297         if (ret)
 298                 return ret;
 299         return set_tls_entry(current, &info, idx, 1);
 300 }
 301
 302 /*
 303  * Perform set_thread_area on behalf of the traced child.
 304  * Note: error handling is not done on the deferred load, and this differ from
 305  * i386. However the only possible error are caused by bugs.
 306  */
 307 int ptrace_set_thread_area(struct task_struct *child, int idx,
 308                 struct user_desc __user *user_desc)
 309 {
 310         struct user_desc info;
 311
 312         if (!host_supports_tls)
 313                 return -EIO;
 314
 315         if (copy_from_user(&info, user_desc, sizeof(info)))
 316                 return -EFAULT;
 317
 318         return set_tls_entry(child, &info, idx, 0);
 319 }
 320
 321 asmlinkage int sys_get_thread_area(struct user_desc __user *user_desc)
 322 {
 323         struct user_desc info;
 324         int idx, ret;
 325
 326         if (!host_supports_tls)
 327                 return -ENOSYS;
 328
 329         if (get_user(idx, &user_desc->entry_number))
 330                 return -EFAULT;
 331
 332         ret = get_tls_entry(current, &info, idx);
 333         if (ret < 0)
 334                 goto out;
 335
 336         if (copy_to_user(user_desc, &info, sizeof(info)))
 337                 ret = -EFAULT;
 338
 339 out:
 340         return ret;
 341 }
 342
 343 /*
 344  * Perform get_thread_area on behalf of the traced child.
 345  */
 346 int ptrace_get_thread_area(struct task_struct *child, int idx,
 347                 struct user_desc __user *user_desc)
 348 {
 349         struct user_desc info;
 350         int ret;
 351
 352         if (!host_supports_tls)
 353                 return -EIO;
 354
 355         ret = get_tls_entry(child, &info, idx);
 356         if (ret < 0)
 357                 goto out;
 358
 359         if (copy_to_user(user_desc, &info, sizeof(info)))
 360                 ret = -EFAULT;
 361 out:
 362         return ret;
 363 }
 364
 365
 366 /* XXX: This part is probably common to i386 and x86-64. Don't create a common
 367  * file for now, do that when implementing x86-64 support.*/
 368 static int __init __setup_host_supports_tls(void)
 369 {
 370         check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
 371         if (host_supports_tls) {
 372                 printk(KERN_INFO "Host TLS support detected\n");
 373                 printk(KERN_INFO "Detected host type: ");
 374                 switch (host_gdt_entry_tls_min) {
 375                         case GDT_ENTRY_TLS_MIN_I386:
 376                                 printk("i386\n");
 377                                 break;
 378                         case GDT_ENTRY_TLS_MIN_X86_64:
 379                                 printk("x86_64\n");
 380                                 break;
 381                 }
 382         } else
 383                 printk(KERN_ERR "  Host TLS support NOT detected! "
 384                                 "TLS support inside UML will not work\n");
 385         return 0;
 386 }
 387
 388 __initcall(__setup_host_supports_tls);