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