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