kernel/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 <asm/uaccess.h>
  10 #include <os.h>
  11 #include <skas.h>
  12 #include <sysdep/tls.h>
  13
  14 /*
  15  * If needed we can detect when it's uninitialized.
  16  *
  17  * These are initialized in an initcall and unchanged thereafter.
  18  */
  19 static int host_supports_tls = -1;
  20 int host_gdt_entry_tls_min;
  21
  22 int do_set_thread_area(struct user_desc *info)
  23 {
  24         int ret;
  25         u32 cpu;
  26
  27         cpu = get_cpu();
  28         ret = os_set_thread_area(info, userspace_pid[cpu]);
  29         put_cpu();
  30
  31         if (ret)
  32                 printk(KERN_ERR "PTRACE_SET_THREAD_AREA failed, err = %d, "
  33                        "index = %d\n", ret, info->entry_number);
  34
  35         return ret;
  36 }
  37
  38 int do_get_thread_area(struct user_desc *info)
  39 {
  40         int ret;
  41         u32 cpu;
  42
  43         cpu = get_cpu();
  44         ret = os_get_thread_area(info, userspace_pid[cpu]);
  45         put_cpu();
  46
  47         if (ret)
  48                 printk(KERN_ERR "PTRACE_GET_THREAD_AREA failed, err = %d, "
  49                        "index = %d\n", ret, info->entry_number);
  50
  51         return ret;
  52 }
  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 dynamic 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         /*
  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 =
  98                         &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];
  99
 100                 /*
 101                  * Actually, now if it wasn't flushed it gets cleared and
 102                  * flushed to the host, which will clear it.
 103                  */
 104                 if (!curr->present) {
 105                         if (!curr->flushed) {
 106                                 clear_user_desc(&curr->tls);
 107                                 curr->tls.entry_number = idx;
 108                         } else {
 109                                 WARN_ON(!LDT_empty(&curr->tls));
 110                                 continue;
 111                         }
 112                 }
 113
 114                 if (!(flags & O_FORCE) && curr->flushed)
 115                         continue;
 116
 117                 ret = do_set_thread_area(&curr->tls);
 118                 if (ret)
 119                         goto out;
 120
 121                 curr->flushed = 1;
 122         }
 123 out:
 124         return ret;
 125 }
 126
 127 /*
 128  * Verify if we need to do a flush for the new process, i.e. if there are any
 129  * present desc's, only if they haven't been flushed.
 130  */
 131 static inline int needs_TLS_update(struct task_struct *task)
 132 {
 133         int i;
 134         int ret = 0;
 135
 136         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 137                 struct uml_tls_struct* curr =
 138                         &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 139
 140                 /*
 141                  * Can't test curr->present, we may need to clear a descriptor
 142                  * which had a value.
 143                  */
 144                 if (curr->flushed)
 145                         continue;
 146                 ret = 1;
 147                 break;
 148         }
 149         return ret;
 150 }
 151
 152 /*
 153  * On a newly forked process, the TLS descriptors haven't yet been flushed. So
 154  * we mark them as such and the first switch_to will do the job.
 155  */
 156 void clear_flushed_tls(struct task_struct *task)
 157 {
 158         int i;
 159
 160         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 161                 struct uml_tls_struct* curr =
 162                         &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 163
 164                 /*
 165                  * Still correct to do this, if it wasn't present on the host it
 166                  * will remain as flushed as it was.
 167                  */
 168                 if (!curr->present)
 169                         continue;
 170
 171                 curr->flushed = 0;
 172         }
 173 }
 174
 175 /*
 176  * In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
 177  * common host process. So this is needed in SKAS0 too.
 178  *
 179  * However, if each thread had a different host process (and this was discussed
 180  * for SMP support) this won't be needed.
 181  *
 182  * And this will not need be used when (and if) we'll add support to the host
 183  * SKAS patch.
 184  */
 185
 186 int arch_switch_tls(struct task_struct *to)
 187 {
 188         if (!host_supports_tls)
 189                 return 0;
 190
 191         /*
 192          * We have no need whatsoever to switch TLS for kernel threads; beyond
 193          * that, that would also result in us calling os_set_thread_area with
 194          * userspace_pid[cpu] == 0, which gives an error.
 195          */
 196         if (likely(to->mm))
 197                 return load_TLS(O_FORCE, to);
 198
 199         return 0;
 200 }
 201
 202 static int set_tls_entry(struct task_struct* task, struct user_desc *info,
 203                          int idx, int flushed)
 204 {
 205         struct thread_struct *t = &task->thread;
 206
 207         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 208                 return -EINVAL;
 209
 210         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info;
 211         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1;
 212         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed;
 213
 214         return 0;
 215 }
 216
 217 int arch_copy_tls(struct task_struct *new)
 218 {
 219         struct user_desc info;
 220         int idx, ret = -EFAULT;
 221
 222         if (copy_from_user(&info,
 223                            (void __user *) UPT_SI(&new->thread.regs.regs),
 224                            sizeof(info)))
 225                 goto out;
 226
 227         ret = -EINVAL;
 228         if (LDT_empty(&info))
 229                 goto out;
 230
 231         idx = info.entry_number;
 232
 233         ret = set_tls_entry(new, &info, idx, 0);
 234 out:
 235         return ret;
 236 }
 237
 238 /* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */
 239 static int get_tls_entry(struct task_struct *task, struct user_desc *info,
 240                          int idx)
 241 {
 242         struct thread_struct *t = &task->thread;
 243
 244         if (!t->arch.tls_array)
 245                 goto clear;
 246
 247         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 248                 return -EINVAL;
 249
 250         if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present)
 251                 goto clear;
 252
 253         *info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls;
 254
 255 out:
 256         /*
 257          * Temporary debugging check, to make sure that things have been
 258          * flushed. This could be triggered if load_TLS() failed.
 259          */
 260         if (unlikely(task == current &&
 261                      !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) {
 262                 printk(KERN_ERR "get_tls_entry: task with pid %d got here "
 263                                 "without flushed TLS.", current->pid);
 264         }
 265
 266         return 0;
 267 clear:
 268         /*
 269          * When the TLS entry has not been set, the values read to user in the
 270          * tls_array are 0 (because it's cleared at boot, see
 271          * arch/i386/kernel/head.S:cpu_gdt_table). Emulate that.
 272          */
 273         clear_user_desc(info);
 274         info->entry_number = idx;
 275         goto out;
 276 }
 277
 278 SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, user_desc)
 279 {
 280         struct user_desc info;
 281         int idx, ret;
 282
 283         if (!host_supports_tls)
 284                 return -ENOSYS;
 285
 286         if (copy_from_user(&info, user_desc, sizeof(info)))
 287                 return -EFAULT;
 288
 289         idx = info.entry_number;
 290
 291         if (idx == -1) {
 292                 idx = get_free_idx(current);
 293                 if (idx < 0)
 294                         return idx;
 295                 info.entry_number = idx;
 296                 /* Tell the user which slot we chose for him.*/
 297                 if (put_user(idx, &user_desc->entry_number))
 298                         return -EFAULT;
 299         }
 300
 301         ret = do_set_thread_area(&info);
 302         if (ret)
 303                 return ret;
 304         return set_tls_entry(current, &info, idx, 1);
 305 }
 306
 307 /*
 308  * Perform set_thread_area on behalf of the traced child.
 309  * Note: error handling is not done on the deferred load, and this differ from
 310  * i386. However the only possible error are caused by bugs.
 311  */
 312 int ptrace_set_thread_area(struct task_struct *child, int idx,
 313                            struct user_desc __user *user_desc)
 314 {
 315         struct user_desc info;
 316
 317         if (!host_supports_tls)
 318                 return -EIO;
 319
 320         if (copy_from_user(&info, user_desc, sizeof(info)))
 321                 return -EFAULT;
 322
 323         return set_tls_entry(child, &info, idx, 0);
 324 }
 325
 326 SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, user_desc)
 327 {
 328         struct user_desc info;
 329         int idx, ret;
 330
 331         if (!host_supports_tls)
 332                 return -ENOSYS;
 333
 334         if (get_user(idx, &user_desc->entry_number))
 335                 return -EFAULT;
 336
 337         ret = get_tls_entry(current, &info, idx);
 338         if (ret < 0)
 339                 goto out;
 340
 341         if (copy_to_user(user_desc, &info, sizeof(info)))
 342                 ret = -EFAULT;
 343
 344 out:
 345         return ret;
 346 }
 347
 348 /*
 349  * Perform get_thread_area on behalf of the traced child.
 350  */
 351 int ptrace_get_thread_area(struct task_struct *child, int idx,
 352                 struct user_desc __user *user_desc)
 353 {
 354         struct user_desc info;
 355         int ret;
 356
 357         if (!host_supports_tls)
 358                 return -EIO;
 359
 360         ret = get_tls_entry(child, &info, idx);
 361         if (ret < 0)
 362                 goto out;
 363
 364         if (copy_to_user(user_desc, &info, sizeof(info)))
 365                 ret = -EFAULT;
 366 out:
 367         return ret;
 368 }
 369
 370 /*
 371  * This code is really i386-only, but it detects and logs x86_64 GDT indexes
 372  * if a 32-bit UML is running on a 64-bit host.
 373  */
 374 static int __init __setup_host_supports_tls(void)
 375 {
 376         check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
 377         if (host_supports_tls) {
 378                 printk(KERN_INFO "Host TLS support detected\n");
 379                 printk(KERN_INFO "Detected host type: ");
 380                 switch (host_gdt_entry_tls_min) {
 381                 case GDT_ENTRY_TLS_MIN_I386:
 382                         printk(KERN_CONT "i386");
 383                         break;
 384                 case GDT_ENTRY_TLS_MIN_X86_64:
 385                         printk(KERN_CONT "x86_64");
 386                         break;
 387                 }
 388                 printk(KERN_CONT " (GDT indexes %d to %d)\n",
 389                        host_gdt_entry_tls_min,
 390                        host_gdt_entry_tls_min + GDT_ENTRY_TLS_ENTRIES);
 391         } else
 392                 printk(KERN_ERR "  Host TLS support NOT detected! "
 393                                 "TLS support inside UML will not work\n");
 394         return 0;
 395 }
 396
 397 __initcall(__setup_host_supports_tls);