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