arch/x86/um/tls_32.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 <linux/syscalls.h>
   9 #include <linux/uaccess.h>
  10 #include <asm/ptrace-abi.h>
  11 #include <os.h>
  12 #include <skas.h>
  13 #include <sysdep/tls.h>
  14
  15 /*
  16  * If needed we can detect when it's uninitialized.
  17  *
  18  * These are initialized in an initcall and unchanged thereafter.
  19  */
  20 static int host_supports_tls = -1;
  21 int host_gdt_entry_tls_min;
  22
  23 static int do_set_thread_area(struct user_desc *info)
  24 {
  25         int ret;
  26         u32 cpu;
  27
  28         cpu = get_cpu();
  29         ret = os_set_thread_area(info, userspace_pid[cpu]);
  30         put_cpu();
  31
  32         if (ret)
  33                 printk(KERN_ERR "PTRACE_SET_THREAD_AREA failed, err = %d, "
  34                        "index = %d\n", ret, info->entry_number);
  35
  36         return ret;
  37 }
  38
  39 /*
  40  * sys_get_thread_area: get a yet unused TLS descriptor index.
  41  * XXX: Consider leaving one free slot for glibc usage at first place. This must
  42  * be done here (and by changing GDT_ENTRY_TLS_* macros) and nowhere else.
  43  *
  44  * Also, this must be tested when compiling in SKAS mode with dynamic linking
  45  * and running against NPTL.
  46  */
  47 static int get_free_idx(struct task_struct* task)
  48 {
  49         struct thread_struct *t = &task->thread;
  50         int idx;
  51
  52         for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
  53                 if (!t->arch.tls_array[idx].present)
  54                         return idx + GDT_ENTRY_TLS_MIN;
  55         return -ESRCH;
  56 }
  57
  58 static inline void clear_user_desc(struct user_desc* info)
  59 {
  60         /* Postcondition: LDT_empty(info) returns true. */
  61         memset(info, 0, sizeof(*info));
  62
  63         /*
  64          * Check the LDT_empty or the i386 sys_get_thread_area code - we obtain
  65          * indeed an empty user_desc.
  66          */
  67         info->read_exec_only = 1;
  68         info->seg_not_present = 1;
  69 }
  70
  71 #define O_FORCE 1
  72
  73 static int load_TLS(int flags, struct task_struct *to)
  74 {
  75         int ret = 0;
  76         int idx;
  77
  78         for (idx = GDT_ENTRY_TLS_MIN; idx < GDT_ENTRY_TLS_MAX; idx++) {
  79                 struct uml_tls_struct* curr =
  80                         &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];
  81
  82                 /*
  83                  * Actually, now if it wasn't flushed it gets cleared and
  84                  * flushed to the host, which will clear it.
  85                  */
  86                 if (!curr->present) {
  87                         if (!curr->flushed) {
  88                                 clear_user_desc(&curr->tls);
  89                                 curr->tls.entry_number = idx;
  90                         } else {
  91                                 WARN_ON(!LDT_empty(&curr->tls));
  92                                 continue;
  93                         }
  94                 }
  95
  96                 if (!(flags & O_FORCE) && curr->flushed)
  97                         continue;
  98
  99                 ret = do_set_thread_area(&curr->tls);
 100                 if (ret)
 101                         goto out;
 102
 103                 curr->flushed = 1;
 104         }
 105 out:
 106         return ret;
 107 }
 108
 109 /*
 110  * Verify if we need to do a flush for the new process, i.e. if there are any
 111  * present desc's, only if they haven't been flushed.
 112  */
 113 static inline int needs_TLS_update(struct task_struct *task)
 114 {
 115         int i;
 116         int ret = 0;
 117
 118         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 119                 struct uml_tls_struct* curr =
 120                         &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 121
 122                 /*
 123                  * Can't test curr->present, we may need to clear a descriptor
 124                  * which had a value.
 125                  */
 126                 if (curr->flushed)
 127                         continue;
 128                 ret = 1;
 129                 break;
 130         }
 131         return ret;
 132 }
 133
 134 /*
 135  * On a newly forked process, the TLS descriptors haven't yet been flushed. So
 136  * we mark them as such and the first switch_to will do the job.
 137  */
 138 void clear_flushed_tls(struct task_struct *task)
 139 {
 140         int i;
 141
 142         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 143                 struct uml_tls_struct* curr =
 144                         &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 145
 146                 /*
 147                  * Still correct to do this, if it wasn't present on the host it
 148                  * will remain as flushed as it was.
 149                  */
 150                 if (!curr->present)
 151                         continue;
 152
 153                 curr->flushed = 0;
 154         }
 155 }
 156
 157 /*
 158  * In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
 159  * common host process. So this is needed in SKAS0 too.
 160  *
 161  * However, if each thread had a different host process (and this was discussed
 162  * for SMP support) this won't be needed.
 163  *
 164  * And this will not need be used when (and if) we'll add support to the host
 165  * SKAS patch.
 166  */
 167
 168 int arch_switch_tls(struct task_struct *to)
 169 {
 170         if (!host_supports_tls)
 171                 return 0;
 172
 173         /*
 174          * We have no need whatsoever to switch TLS for kernel threads; beyond
 175          * that, that would also result in us calling os_set_thread_area with
 176          * userspace_pid[cpu] == 0, which gives an error.
 177          */
 178         if (likely(to->mm))
 179                 return load_TLS(O_FORCE, to);
 180
 181         return 0;
 182 }
 183
 184 static int set_tls_entry(struct task_struct* task, struct user_desc *info,
 185                          int idx, int flushed)
 186 {
 187         struct thread_struct *t = &task->thread;
 188
 189         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 190                 return -EINVAL;
 191
 192         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info;
 193         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1;
 194         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed;
 195
 196         return 0;
 197 }
 198
 199 int arch_set_tls(struct task_struct *new, unsigned long tls)
 200 {
 201         struct user_desc info;
 202         int idx, ret = -EFAULT;
 203
 204         if (copy_from_user(&info, (void __user *) tls, 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 static int get_tls_entry(struct task_struct *task, struct user_desc *info,
 219                          int idx)
 220 {
 221         struct thread_struct *t = &task->thread;
 222
 223         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 224                 return -EINVAL;
 225
 226         if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present)
 227                 goto clear;
 228
 229         *info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls;
 230
 231 out:
 232         /*
 233          * Temporary debugging check, to make sure that things have been
 234          * flushed. This could be triggered if load_TLS() failed.
 235          */
 236         if (unlikely(task == current &&
 237                      !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) {
 238                 printk(KERN_ERR "get_tls_entry: task with pid %d got here "
 239                                 "without flushed TLS.", current->pid);
 240         }
 241
 242         return 0;
 243 clear:
 244         /*
 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 SYSCALL_DEFINE1(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 SYSCALL_DEFINE1(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  * This code is really i386-only, but it detects and logs x86_64 GDT indexes
 348  * if a 32-bit UML is running on a 64-bit host.
 349  */
 350 static int __init __setup_host_supports_tls(void)
 351 {
 352         check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
 353         if (host_supports_tls) {
 354                 printk(KERN_INFO "Host TLS support detected\n");
 355                 printk(KERN_INFO "Detected host type: ");
 356                 switch (host_gdt_entry_tls_min) {
 357                 case GDT_ENTRY_TLS_MIN_I386:
 358                         printk(KERN_CONT "i386");
 359                         break;
 360                 case GDT_ENTRY_TLS_MIN_X86_64:
 361                         printk(KERN_CONT "x86_64");
 362                         break;
 363                 }
 364                 printk(KERN_CONT " (GDT indexes %d to %d)\n",
 365                        host_gdt_entry_tls_min,
 366                        host_gdt_entry_tls_min + GDT_ENTRY_TLS_ENTRIES);
 367         } else
 368                 printk(KERN_ERR "  Host TLS support NOT detected! "
 369                                 "TLS support inside UML will not work\n");
 370         return 0;
 371 }
 372
 373 __initcall(__setup_host_supports_tls);