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/percpu.h"
   7 #include "linux/sched.h"
   8 #include "asm/uaccess.h"
   9 #include "os.h"
  10 #include "skas.h"
  11 #include "sysdep/tls.h"
  12
  13 /*
  14  * If needed we can detect when it's uninitialized.
  15  *
  16  * These are initialized in an initcall and unchanged thereafter.
  17  */
  18 static int host_supports_tls = -1;
  19 int host_gdt_entry_tls_min;
  20
  21 int do_set_thread_area(struct user_desc *info)
  22 {
  23         int ret;
  24         u32 cpu;
  25
  26         cpu = get_cpu();
  27         ret = os_set_thread_area(info, userspace_pid[cpu]);
  28         put_cpu();
  29
  30         if (ret)
  31                 printk(KERN_ERR "PTRACE_SET_THREAD_AREA failed, err = %d, "
  32                        "index = %d\n", ret, info->entry_number);
  33
  34         return ret;
  35 }
  36
  37 int do_get_thread_area(struct user_desc *info)
  38 {
  39         int ret;
  40         u32 cpu;
  41
  42         cpu = get_cpu();
  43         ret = os_get_thread_area(info, userspace_pid[cpu]);
  44         put_cpu();
  45
  46         if (ret)
  47                 printk(KERN_ERR "PTRACE_GET_THREAD_AREA failed, err = %d, "
  48                        "index = %d\n", ret, info->entry_number);
  49
  50         return ret;
  51 }
  52
  53 /*
  54  * sys_get_thread_area: get a yet unused TLS descriptor index.
  55  * XXX: Consider leaving one free slot for glibc usage at first place. This must
  56  * be done here (and by changing GDT_ENTRY_TLS_* macros) and nowhere else.
  57  *
  58  * Also, this must be tested when compiling in SKAS mode with dynamic linking
  59  * and running against NPTL.
  60  */
  61 static int get_free_idx(struct task_struct* task)
  62 {
  63         struct thread_struct *t = &task->thread;
  64         int idx;
  65
  66         if (!t->arch.tls_array)
  67                 return GDT_ENTRY_TLS_MIN;
  68
  69         for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
  70                 if (!t->arch.tls_array[idx].present)
  71                         return idx + GDT_ENTRY_TLS_MIN;
  72         return -ESRCH;
  73 }
  74
  75 static inline void clear_user_desc(struct user_desc* info)
  76 {
  77         /* Postcondition: LDT_empty(info) returns true. */
  78         memset(info, 0, sizeof(*info));
  79
  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 =
  97                         &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];
  98
  99                 /*
 100                  * Actually, now if it wasn't flushed it gets cleared and
 101                  * flushed to the host, which will clear it.
 102                  */
 103                 if (!curr->present) {
 104                         if (!curr->flushed) {
 105                                 clear_user_desc(&curr->tls);
 106                                 curr->tls.entry_number = idx;
 107                         } else {
 108                                 WARN_ON(!LDT_empty(&curr->tls));
 109                                 continue;
 110                         }
 111                 }
 112
 113                 if (!(flags & O_FORCE) && curr->flushed)
 114                         continue;
 115
 116                 ret = do_set_thread_area(&curr->tls);
 117                 if (ret)
 118                         goto out;
 119
 120                 curr->flushed = 1;
 121         }
 122 out:
 123         return ret;
 124 }
 125
 126 /*
 127  * Verify if we need to do a flush for the new process, i.e. if there are any
 128  * present desc's, only if they haven't been flushed.
 129  */
 130 static inline int needs_TLS_update(struct task_struct *task)
 131 {
 132         int i;
 133         int ret = 0;
 134
 135         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 136                 struct uml_tls_struct* curr =
 137                         &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 138
 139                 /*
 140                  * Can't test curr->present, we may need to clear a descriptor
 141                  * which had a value.
 142                  */
 143                 if (curr->flushed)
 144                         continue;
 145                 ret = 1;
 146                 break;
 147         }
 148         return ret;
 149 }
 150
 151 /*
 152  * On a newly forked process, the TLS descriptors haven't yet been flushed. So
 153  * we mark them as such and the first switch_to will do the job.
 154  */
 155 void clear_flushed_tls(struct task_struct *task)
 156 {
 157         int i;
 158
 159         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 160                 struct uml_tls_struct* curr =
 161                         &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 162
 163                 /*
 164                  * Still correct to do this, if it wasn't present on the host it
 165                  * will remain as flushed as it was.
 166                  */
 167                 if (!curr->present)
 168                         continue;
 169
 170                 curr->flushed = 0;
 171         }
 172 }
 173
 174 /*
 175  * In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
 176  * common host process. So this is needed in SKAS0 too.
 177  *
 178  * However, if each thread had a different host process (and this was discussed
 179  * for SMP support) this won't be needed.
 180  *
 181  * And this will not need be used when (and if) we'll add support to the host
 182  * SKAS patch.
 183  */
 184
 185 int arch_switch_tls(struct task_struct *to)
 186 {
 187         if (!host_supports_tls)
 188                 return 0;
 189
 190         /*
 191          * We have no need whatsoever to switch TLS for kernel threads; beyond
 192          * that, that would also result in us calling os_set_thread_area with
 193          * userspace_pid[cpu] == 0, which gives an error.
 194          */
 195         if (likely(to->mm))
 196                 return load_TLS(O_FORCE, to);
 197
 198         return 0;
 199 }
 200
 201 static int set_tls_entry(struct task_struct* task, struct user_desc *info,
 202                          int idx, int flushed)
 203 {
 204         struct thread_struct *t = &task->thread;
 205
 206         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 207                 return -EINVAL;
 208
 209         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info;
 210         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1;
 211         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed;
 212
 213         return 0;
 214 }
 215
 216 int arch_copy_tls(struct task_struct *new)
 217 {
 218         struct user_desc info;
 219         int idx, ret = -EFAULT;
 220
 221         if (copy_from_user(&info,
 222                            (void __user *) UPT_ESI(&new->thread.regs.regs),
 223                            sizeof(info)))
 224                 goto out;
 225
 226         ret = -EINVAL;
 227         if (LDT_empty(&info))
 228                 goto out;
 229
 230         idx = info.entry_number;
 231
 232         ret = set_tls_entry(new, &info, idx, 0);
 233 out:
 234         return ret;
 235 }
 236
 237 /* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */
 238 static int get_tls_entry(struct task_struct *task, struct user_desc *info,
 239                          int idx)
 240 {
 241         struct thread_struct *t = &task->thread;
 242
 243         if (!t->arch.tls_array)
 244                 goto clear;
 245
 246         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 247                 return -EINVAL;
 248
 249         if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present)
 250                 goto clear;
 251
 252         *info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls;
 253
 254 out:
 255         /*
 256          * Temporary debugging check, to make sure that things have been
 257          * flushed. This could be triggered if load_TLS() failed.
 258          */
 259         if (unlikely(task == current &&
 260                      !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) {
 261                 printk(KERN_ERR "get_tls_entry: task with pid %d got here "
 262                                 "without flushed TLS.", current->pid);
 263         }
 264
 265         return 0;
 266 clear:
 267         /*
 268          * When the TLS entry has not been set, the values read to user in the
 269          * tls_array are 0 (because it's cleared at boot, see
 270          * arch/i386/kernel/head.S:cpu_gdt_table). Emulate that.
 271          */
 272         clear_user_desc(info);
 273         info->entry_number = idx;
 274         goto out;
 275 }
 276
 277 int sys_set_thread_area(struct user_desc __user *user_desc)
 278 {
 279         struct user_desc info;
 280         int idx, ret;
 281
 282         if (!host_supports_tls)
 283                 return -ENOSYS;
 284
 285         if (copy_from_user(&info, user_desc, sizeof(info)))
 286                 return -EFAULT;
 287
 288         idx = info.entry_number;
 289
 290         if (idx == -1) {
 291                 idx = get_free_idx(current);
 292                 if (idx < 0)
 293                         return idx;
 294                 info.entry_number = idx;
 295                 /* Tell the user which slot we chose for him.*/
 296                 if (put_user(idx, &user_desc->entry_number))
 297                         return -EFAULT;
 298         }
 299
 300         ret = do_set_thread_area(&info);
 301         if (ret)
 302                 return ret;
 303         return set_tls_entry(current, &info, idx, 1);
 304 }
 305
 306 /*
 307  * Perform set_thread_area on behalf of the traced child.
 308  * Note: error handling is not done on the deferred load, and this differ from
 309  * i386. However the only possible error are caused by bugs.
 310  */
 311 int ptrace_set_thread_area(struct task_struct *child, int idx,
 312                            struct user_desc __user *user_desc)
 313 {
 314         struct user_desc info;
 315
 316         if (!host_supports_tls)
 317                 return -EIO;
 318
 319         if (copy_from_user(&info, user_desc, sizeof(info)))
 320                 return -EFAULT;
 321
 322         return set_tls_entry(child, &info, idx, 0);
 323 }
 324
 325 int sys_get_thread_area(struct user_desc __user *user_desc)
 326 {
 327         struct user_desc info;
 328         int idx, ret;
 329
 330         if (!host_supports_tls)
 331                 return -ENOSYS;
 332
 333         if (get_user(idx, &user_desc->entry_number))
 334                 return -EFAULT;
 335
 336         ret = get_tls_entry(current, &info, idx);
 337         if (ret < 0)
 338                 goto out;
 339
 340         if (copy_to_user(user_desc, &info, sizeof(info)))
 341                 ret = -EFAULT;
 342
 343 out:
 344         return ret;
 345 }
 346
 347 /*
 348  * Perform get_thread_area on behalf of the traced child.
 349  */
 350 int ptrace_get_thread_area(struct task_struct *child, int idx,
 351                 struct user_desc __user *user_desc)
 352 {
 353         struct user_desc info;
 354         int ret;
 355
 356         if (!host_supports_tls)
 357                 return -EIO;
 358
 359         ret = get_tls_entry(child, &info, idx);
 360         if (ret < 0)
 361                 goto out;
 362
 363         if (copy_to_user(user_desc, &info, sizeof(info)))
 364                 ret = -EFAULT;
 365 out:
 366         return ret;
 367 }
 368
 369 /*
 370  * This code is really i386-only, but it detects and logs x86_64 GDT indexes
 371  * if a 32-bit UML is running on a 64-bit host.
 372  */
 373 static int __init __setup_host_supports_tls(void)
 374 {
 375         check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
 376         if (host_supports_tls) {
 377                 printk(KERN_INFO "Host TLS support detected\n");
 378                 printk(KERN_INFO "Detected host type: ");
 379                 switch (host_gdt_entry_tls_min) {
 380                 case GDT_ENTRY_TLS_MIN_I386:
 381                         printk(KERN_CONT "i386");
 382                         break;
 383                 case GDT_ENTRY_TLS_MIN_X86_64:
 384                         printk(KERN_CONT "x86_64");
 385                         break;
 386                 }
 387                 printk(KERN_CONT " (GDT indexes %d to %d)\n",
 388                        host_gdt_entry_tls_min,
 389                        host_gdt_entry_tls_min + GDT_ENTRY_TLS_ENTRIES);
 390         } else
 391                 printk(KERN_ERR "  Host TLS support NOT detected! "
 392                                 "TLS support inside UML will not work\n");
 393         return 0;
 394 }
 395
 396 __initcall(__setup_host_supports_tls);