SAFE public projects git trees. - safe/jmp/linux-2.6/blob - 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 "kern.h"
  16 #include "kern_util.h"
  17 #include "os.h"
  18 #include "skas.h"
  19
  20 /*
  21  * If needed we can detect when it's uninitialized.
  22  *
  23  * These are initialized in an initcall and unchanged thereafter.
  24  */
  25 static int host_supports_tls = -1;
  26 int host_gdt_entry_tls_min;
  27
  28 int do_set_thread_area(struct user_desc *info)
  29 {
  30         int ret;
  31         u32 cpu;
  32
  33         cpu = get_cpu();
  34         ret = os_set_thread_area(info, userspace_pid[cpu]);
  35         put_cpu();
  36         return ret;
  37 }
  38
  39 int do_get_thread_area(struct user_desc *info)
  40 {
  41         int ret;
  42         u32 cpu;
  43
  44         cpu = get_cpu();
  45         ret = os_get_thread_area(info, userspace_pid[cpu]);
  46         put_cpu();
  47         return ret;
  48 }
  49
  50 /*
  51  * sys_get_thread_area: get a yet unused TLS descriptor index.
  52  * XXX: Consider leaving one free slot for glibc usage at first place. This must
  53  * be done here (and by changing GDT_ENTRY_TLS_* macros) and nowhere else.
  54  *
  55  * Also, this must be tested when compiling in SKAS mode with dinamic linking
  56  * and running against NPTL.
  57  */
  58 static int get_free_idx(struct task_struct* task)
  59 {
  60         struct thread_struct *t = &task->thread;
  61         int idx;
  62
  63         if (!t->arch.tls_array)
  64                 return GDT_ENTRY_TLS_MIN;
  65
  66         for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
  67                 if (!t->arch.tls_array[idx].present)
  68                         return idx + GDT_ENTRY_TLS_MIN;
  69         return -ESRCH;
  70 }
  71
  72 static inline void clear_user_desc(struct user_desc* info)
  73 {
  74         /* Postcondition: LDT_empty(info) returns true. */
  75         memset(info, 0, sizeof(*info));
  76
  77         /* Check the LDT_empty or the i386 sys_get_thread_area code - we obtain
  78          * indeed an empty user_desc.
  79          */
  80         info->read_exec_only = 1;
  81         info->seg_not_present = 1;
  82 }
  83
  84 #define O_FORCE 1
  85
  86 static int load_TLS(int flags, struct task_struct *to)
  87 {
  88         int ret = 0;
  89         int idx;
  90
  91         for (idx = GDT_ENTRY_TLS_MIN; idx < GDT_ENTRY_TLS_MAX; idx++) {
  92                 struct uml_tls_struct* curr = &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];
  93
  94                 /* Actually, now if it wasn't flushed it gets cleared and
  95                  * flushed to the host, which will clear it.*/
  96                 if (!curr->present) {
  97                         if (!curr->flushed) {
  98                                 clear_user_desc(&curr->tls);
  99                                 curr->tls.entry_number = idx;
 100                         } else {
 101                                 WARN_ON(!LDT_empty(&curr->tls));
 102                                 continue;
 103                         }
 104                 }
 105
 106                 if (!(flags & O_FORCE) && curr->flushed)
 107                         continue;
 108
 109                 ret = do_set_thread_area(&curr->tls);
 110                 if (ret)
 111                         goto out;
 112
 113                 curr->flushed = 1;
 114         }
 115 out:
 116         return ret;
 117 }
 118
 119 /* Verify if we need to do a flush for the new process, i.e. if there are any
 120  * present desc's, only if they haven't been flushed.
 121  */
 122 static inline int needs_TLS_update(struct task_struct *task)
 123 {
 124         int i;
 125         int ret = 0;
 126
 127         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 128                 struct uml_tls_struct* curr = &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 129
 130                 /* Can't test curr->present, we may need to clear a descriptor
 131                  * which had a value. */
 132                 if (curr->flushed)
 133                         continue;
 134                 ret = 1;
 135                 break;
 136         }
 137         return ret;
 138 }
 139
 140 /* On a newly forked process, the TLS descriptors haven't yet been flushed. So
 141  * we mark them as such and the first switch_to will do the job.
 142  */
 143 void clear_flushed_tls(struct task_struct *task)
 144 {
 145         int i;
 146
 147         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 148                 struct uml_tls_struct* curr = &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 149
 150                 /* Still correct to do this, if it wasn't present on the host it
 151                  * will remain as flushed as it was. */
 152                 if (!curr->present)
 153                         continue;
 154
 155                 curr->flushed = 0;
 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 int arch_switch_tls(struct task_struct *from, struct task_struct *to)
 169 {
 170         if (!host_supports_tls)
 171                 return 0;
 172
 173         /* We have no need whatsoever to switch TLS for kernel threads; beyond
 174          * that, that would also result in us calling os_set_thread_area with
 175          * userspace_pid[cpu] == 0, which gives an error. */
 176         if (likely(to->mm))
 177                 return load_TLS(O_FORCE, to);
 178
 179         return 0;
 180 }
 181
 182 static int set_tls_entry(struct task_struct* task, struct user_desc *info,
 183                          int idx, int flushed)
 184 {
 185         struct thread_struct *t = &task->thread;
 186
 187         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 188                 return -EINVAL;
 189
 190         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info;
 191         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1;
 192         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed;
 193
 194         return 0;
 195 }
 196
 197 int arch_copy_tls(struct task_struct *new)
 198 {
 199         struct user_desc info;
 200         int idx, ret = -EFAULT;
 201
 202         if (copy_from_user(&info,
 203                            (void __user *) UPT_ESI(&new->thread.regs.regs),
 204                            sizeof(info)))
 205                 goto out;
 206
 207         ret = -EINVAL;
 208         if (LDT_empty(&info))
 209                 goto out;
 210
 211         idx = info.entry_number;
 212
 213         ret = set_tls_entry(new, &info, idx, 0);
 214 out:
 215         return ret;
 216 }
 217
 218 /* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */
 219 static int get_tls_entry(struct task_struct* task, struct user_desc *info, int idx)
 220 {
 221         struct thread_struct *t = &task->thread;
 222
 223         if (!t->arch.tls_array)
 224                 goto clear;
 225
 226         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 227                 return -EINVAL;
 228
 229         if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present)
 230                 goto clear;
 231
 232         *info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls;
 233
 234 out:
 235         /* Temporary debugging check, to make sure that things have been
 236          * flushed. This could be triggered if load_TLS() failed.
 237          */
 238         if (unlikely(task == current && !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         /* When the TLS entry has not been set, the values read to user in the
 246          * tls_array are 0 (because it's cleared at boot, see
 247          * arch/i386/kernel/head.S:cpu_gdt_table). Emulate that.
 248          */
 249         clear_user_desc(info);
 250         info->entry_number = idx;
 251         goto out;
 252 }
 253
 254 asmlinkage int sys_set_thread_area(struct user_desc __user *user_desc)
 255 {
 256         struct user_desc info;
 257         int idx, ret;
 258
 259         if (!host_supports_tls)
 260                 return -ENOSYS;
 261
 262         if (copy_from_user(&info, user_desc, sizeof(info)))
 263                 return -EFAULT;
 264
 265         idx = info.entry_number;
 266
 267         if (idx == -1) {
 268                 idx = get_free_idx(current);
 269                 if (idx < 0)
 270                         return idx;
 271                 info.entry_number = idx;
 272                 /* Tell the user which slot we chose for him.*/
 273                 if (put_user(idx, &user_desc->entry_number))
 274                         return -EFAULT;
 275         }
 276
 277         ret = do_set_thread_area(&info);
 278         if (ret)
 279                 return ret;
 280         return set_tls_entry(current, &info, idx, 1);
 281 }
 282
 283 /*
 284  * Perform set_thread_area on behalf of the traced child.
 285  * Note: error handling is not done on the deferred load, and this differ from
 286  * i386. However the only possible error are caused by bugs.
 287  */
 288 int ptrace_set_thread_area(struct task_struct *child, int idx,
 289                 struct user_desc __user *user_desc)
 290 {
 291         struct user_desc info;
 292
 293         if (!host_supports_tls)
 294                 return -EIO;
 295
 296         if (copy_from_user(&info, user_desc, sizeof(info)))
 297                 return -EFAULT;
 298
 299         return set_tls_entry(child, &info, idx, 0);
 300 }
 301
 302 asmlinkage int sys_get_thread_area(struct user_desc __user *user_desc)
 303 {
 304         struct user_desc info;
 305         int idx, ret;
 306
 307         if (!host_supports_tls)
 308                 return -ENOSYS;
 309
 310         if (get_user(idx, &user_desc->entry_number))
 311                 return -EFAULT;
 312
 313         ret = get_tls_entry(current, &info, idx);
 314         if (ret < 0)
 315                 goto out;
 316
 317         if (copy_to_user(user_desc, &info, sizeof(info)))
 318                 ret = -EFAULT;
 319
 320 out:
 321         return ret;
 322 }
 323
 324 /*
 325  * Perform get_thread_area on behalf of the traced child.
 326  */
 327 int ptrace_get_thread_area(struct task_struct *child, int idx,
 328                 struct user_desc __user *user_desc)
 329 {
 330         struct user_desc info;
 331         int ret;
 332
 333         if (!host_supports_tls)
 334                 return -EIO;
 335
 336         ret = get_tls_entry(child, &info, idx);
 337         if (ret < 0)
 338                 goto out;
 339
 340         if (copy_to_user(user_desc, &info, sizeof(info)))
 341                 ret = -EFAULT;
 342 out:
 343         return ret;
 344 }
 345
 346
 347 /* XXX: This part is probably common to i386 and x86-64. Don't create a common
 348  * file for now, do that when implementing x86-64 support.*/
 349 static int __init __setup_host_supports_tls(void)
 350 {
 351         check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
 352         if (host_supports_tls) {
 353                 printk(KERN_INFO "Host TLS support detected\n");
 354                 printk(KERN_INFO "Detected host type: ");
 355                 switch (host_gdt_entry_tls_min) {
 356                         case GDT_ENTRY_TLS_MIN_I386:
 357                                 printk("i386\n");
 358                                 break;
 359                         case GDT_ENTRY_TLS_MIN_X86_64:
 360                                 printk("x86_64\n");
 361                                 break;
 362                 }
 363         } else
 364                 printk(KERN_ERR "  Host TLS support NOT detected! "
 365                                 "TLS support inside UML will not work\n");
 366         return 0;
 367 }
 368
 369 __initcall(__setup_host_supports_tls);