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 <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 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 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
  48         if (ret)
  49                 printk(KERN_ERR "PTRACE_GET_THREAD_AREA failed, err = %d, "
  50                        "index = %d\n", ret, info->entry_number);
  51
  52         return ret;
  53 }
  54
  55 /*
  56  * sys_get_thread_area: get a yet unused TLS descriptor index.
  57  * XXX: Consider leaving one free slot for glibc usage at first place. This must
  58  * be done here (and by changing GDT_ENTRY_TLS_* macros) and nowhere else.
  59  *
  60  * Also, this must be tested when compiling in SKAS mode with dynamic linking
  61  * and running against NPTL.
  62  */
  63 static int get_free_idx(struct task_struct* task)
  64 {
  65         struct thread_struct *t = &task->thread;
  66         int idx;
  67
  68         for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
  69                 if (!t->arch.tls_array[idx].present)
  70                         return idx + GDT_ENTRY_TLS_MIN;
  71         return -ESRCH;
  72 }
  73
  74 static inline void clear_user_desc(struct user_desc* info)
  75 {
  76         /* Postcondition: LDT_empty(info) returns true. */
  77         memset(info, 0, sizeof(*info));
  78
  79         /*
  80          * Check the LDT_empty or the i386 sys_get_thread_area code - we obtain
  81          * indeed an empty user_desc.
  82          */
  83         info->read_exec_only = 1;
  84         info->seg_not_present = 1;
  85 }
  86
  87 #define O_FORCE 1
  88
  89 static int load_TLS(int flags, struct task_struct *to)
  90 {
  91         int ret = 0;
  92         int idx;
  93
  94         for (idx = GDT_ENTRY_TLS_MIN; idx < GDT_ENTRY_TLS_MAX; idx++) {
  95                 struct uml_tls_struct* curr =
  96                         &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];
  97
  98                 /*
  99                  * Actually, now if it wasn't flushed it gets cleared and
 100                  * flushed to the host, which will clear it.
 101                  */
 102                 if (!curr->present) {
 103                         if (!curr->flushed) {
 104                                 clear_user_desc(&curr->tls);
 105                                 curr->tls.entry_number = idx;
 106                         } else {
 107                                 WARN_ON(!LDT_empty(&curr->tls));
 108                                 continue;
 109                         }
 110                 }
 111
 112                 if (!(flags & O_FORCE) && curr->flushed)
 113                         continue;
 114
 115                 ret = do_set_thread_area(&curr->tls);
 116                 if (ret)
 117                         goto out;
 118
 119                 curr->flushed = 1;
 120         }
 121 out:
 122         return ret;
 123 }
 124
 125 /*
 126  * Verify if we need to do a flush for the new process, i.e. if there are any
 127  * present desc's, only if they haven't been flushed.
 128  */
 129 static inline int needs_TLS_update(struct task_struct *task)
 130 {
 131         int i;
 132         int ret = 0;
 133
 134         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 135                 struct uml_tls_struct* curr =
 136                         &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 137
 138                 /*
 139                  * Can't test curr->present, we may need to clear a descriptor
 140                  * which had a value.
 141                  */
 142                 if (curr->flushed)
 143                         continue;
 144                 ret = 1;
 145                 break;
 146         }
 147         return ret;
 148 }
 149
 150 /*
 151  * On a newly forked process, the TLS descriptors haven't yet been flushed. So
 152  * we mark them as such and the first switch_to will do the job.
 153  */
 154 void clear_flushed_tls(struct task_struct *task)
 155 {
 156         int i;
 157
 158         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 159                 struct uml_tls_struct* curr =
 160                         &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 161
 162                 /*
 163                  * Still correct to do this, if it wasn't present on the host it
 164                  * will remain as flushed as it was.
 165                  */
 166                 if (!curr->present)
 167                         continue;
 168
 169                 curr->flushed = 0;
 170         }
 171 }
 172
 173 /*
 174  * In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
 175  * common host process. So this is needed in SKAS0 too.
 176  *
 177  * However, if each thread had a different host process (and this was discussed
 178  * for SMP support) this won't be needed.
 179  *
 180  * And this will not need be used when (and if) we'll add support to the host
 181  * SKAS patch.
 182  */
 183
 184 int arch_switch_tls(struct task_struct *to)
 185 {
 186         if (!host_supports_tls)
 187                 return 0;
 188
 189         /*
 190          * We have no need whatsoever to switch TLS for kernel threads; beyond
 191          * that, that would also result in us calling os_set_thread_area with
 192          * userspace_pid[cpu] == 0, which gives an error.
 193          */
 194         if (likely(to->mm))
 195                 return load_TLS(O_FORCE, to);
 196
 197         return 0;
 198 }
 199
 200 static int set_tls_entry(struct task_struct* task, struct user_desc *info,
 201                          int idx, int flushed)
 202 {
 203         struct thread_struct *t = &task->thread;
 204
 205         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 206                 return -EINVAL;
 207
 208         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info;
 209         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1;
 210         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed;
 211
 212         return 0;
 213 }
 214
 215 int arch_copy_tls(struct task_struct *new)
 216 {
 217         struct user_desc info;
 218         int idx, ret = -EFAULT;
 219
 220         if (copy_from_user(&info,
 221                            (void __user *) UPT_SI(&new->thread.regs.regs),
 222                            sizeof(info)))
 223                 goto out;
 224
 225         ret = -EINVAL;
 226         if (LDT_empty(&info))
 227                 goto out;
 228
 229         idx = info.entry_number;
 230
 231         ret = set_tls_entry(new, &info, idx, 0);
 232 out:
 233         return ret;
 234 }
 235
 236 /* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */
 237 static int get_tls_entry(struct task_struct *task, struct user_desc *info,
 238                          int idx)
 239 {
 240         struct thread_struct *t = &task->thread;
 241
 242         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 243                 return -EINVAL;
 244
 245         if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present)
 246                 goto clear;
 247
 248         *info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls;
 249
 250 out:
 251         /*
 252          * Temporary debugging check, to make sure that things have been
 253          * flushed. This could be triggered if load_TLS() failed.
 254          */
 255         if (unlikely(task == current &&
 256                      !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) {
 257                 printk(KERN_ERR "get_tls_entry: task with pid %d got here "
 258                                 "without flushed TLS.", current->pid);
 259         }
 260
 261         return 0;
 262 clear:
 263         /*
 264          * When the TLS entry has not been set, the values read to user in the
 265          * tls_array are 0 (because it's cleared at boot, see
 266          * arch/i386/kernel/head.S:cpu_gdt_table). Emulate that.
 267          */
 268         clear_user_desc(info);
 269         info->entry_number = idx;
 270         goto out;
 271 }
 272
 273 SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, user_desc)
 274 {
 275         struct user_desc info;
 276         int idx, ret;
 277
 278         if (!host_supports_tls)
 279                 return -ENOSYS;
 280
 281         if (copy_from_user(&info, user_desc, sizeof(info)))
 282                 return -EFAULT;
 283
 284         idx = info.entry_number;
 285
 286         if (idx == -1) {
 287                 idx = get_free_idx(current);
 288                 if (idx < 0)
 289                         return idx;
 290                 info.entry_number = idx;
 291                 /* Tell the user which slot we chose for him.*/
 292                 if (put_user(idx, &user_desc->entry_number))
 293                         return -EFAULT;
 294         }
 295
 296         ret = do_set_thread_area(&info);
 297         if (ret)
 298                 return ret;
 299         return set_tls_entry(current, &info, idx, 1);
 300 }
 301
 302 /*
 303  * Perform set_thread_area on behalf of the traced child.
 304  * Note: error handling is not done on the deferred load, and this differ from
 305  * i386. However the only possible error are caused by bugs.
 306  */
 307 int ptrace_set_thread_area(struct task_struct *child, int idx,
 308                            struct user_desc __user *user_desc)
 309 {
 310         struct user_desc info;
 311
 312         if (!host_supports_tls)
 313                 return -EIO;
 314
 315         if (copy_from_user(&info, user_desc, sizeof(info)))
 316                 return -EFAULT;
 317
 318         return set_tls_entry(child, &info, idx, 0);
 319 }
 320
 321 SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, user_desc)
 322 {
 323         struct user_desc info;
 324         int idx, ret;
 325
 326         if (!host_supports_tls)
 327                 return -ENOSYS;
 328
 329         if (get_user(idx, &user_desc->entry_number))
 330                 return -EFAULT;
 331
 332         ret = get_tls_entry(current, &info, idx);
 333         if (ret < 0)
 334                 goto out;
 335
 336         if (copy_to_user(user_desc, &info, sizeof(info)))
 337                 ret = -EFAULT;
 338
 339 out:
 340         return ret;
 341 }
 342
 343 /*
 344  * Perform get_thread_area on behalf of the traced child.
 345  */
 346 int ptrace_get_thread_area(struct task_struct *child, int idx,
 347                 struct user_desc __user *user_desc)
 348 {
 349         struct user_desc info;
 350         int ret;
 351
 352         if (!host_supports_tls)
 353                 return -EIO;
 354
 355         ret = get_tls_entry(child, &info, idx);
 356         if (ret < 0)
 357                 goto out;
 358
 359         if (copy_to_user(user_desc, &info, sizeof(info)))
 360                 ret = -EFAULT;
 361 out:
 362         return ret;
 363 }
 364
 365 /*
 366  * This code is really i386-only, but it detects and logs x86_64 GDT indexes
 367  * if a 32-bit UML is running on a 64-bit host.
 368  */
 369 static int __init __setup_host_supports_tls(void)
 370 {
 371         check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
 372         if (host_supports_tls) {
 373                 printk(KERN_INFO "Host TLS support detected\n");
 374                 printk(KERN_INFO "Detected host type: ");
 375                 switch (host_gdt_entry_tls_min) {
 376                 case GDT_ENTRY_TLS_MIN_I386:
 377                         printk(KERN_CONT "i386");
 378                         break;
 379                 case GDT_ENTRY_TLS_MIN_X86_64:
 380                         printk(KERN_CONT "x86_64");
 381                         break;
 382                 }
 383                 printk(KERN_CONT " (GDT indexes %d to %d)\n",
 384                        host_gdt_entry_tls_min,
 385                        host_gdt_entry_tls_min + GDT_ENTRY_TLS_ENTRIES);
 386         } else
 387                 printk(KERN_ERR "  Host TLS support NOT detected! "
 388                                 "TLS support inside UML will not work\n");
 389         return 0;
 390 }
 391
 392 __initcall(__setup_host_supports_tls);