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 #include "skas.h"
  22
  23 /*
  24  * If needed we can detect when it's uninitialized.
  25  *
  26  * These are initialized in an initcall and unchanged thereafter.
  27  */
  28 static int host_supports_tls = -1;
  29 int host_gdt_entry_tls_min;
  30
  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
  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 dinamic 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         /* 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 = &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];
  96
  97                 /* Actually, now if it wasn't flushed it gets cleared and
  98                  * flushed to the host, which will clear it.*/
  99                 if (!curr->present) {
 100                         if (!curr->flushed) {
 101                                 clear_user_desc(&curr->tls);
 102                                 curr->tls.entry_number = idx;
 103                         } else {
 104                                 WARN_ON(!LDT_empty(&curr->tls));
 105                                 continue;
 106                         }
 107                 }
 108
 109                 if (!(flags & O_FORCE) && curr->flushed)
 110                         continue;
 111
 112                 ret = do_set_thread_area(&curr->tls);
 113                 if (ret)
 114                         goto out;
 115
 116                 curr->flushed = 1;
 117         }
 118 out:
 119         return ret;
 120 }
 121
 122 /* Verify if we need to do a flush for the new process, i.e. if there are any
 123  * present desc's, only if they haven't been flushed.
 124  */
 125 static inline int needs_TLS_update(struct task_struct *task)
 126 {
 127         int i;
 128         int ret = 0;
 129
 130         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 131                 struct uml_tls_struct* curr = &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 132
 133                 /* Can't test curr->present, we may need to clear a descriptor
 134                  * which had a value. */
 135                 if (curr->flushed)
 136                         continue;
 137                 ret = 1;
 138                 break;
 139         }
 140         return ret;
 141 }
 142
 143 /* On a newly forked process, the TLS descriptors haven't yet been flushed. So
 144  * we mark them as such and the first switch_to will do the job.
 145  */
 146 void clear_flushed_tls(struct task_struct *task)
 147 {
 148         int i;
 149
 150         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 151                 struct uml_tls_struct* curr = &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 152
 153                 /* Still correct to do this, if it wasn't present on the host it
 154                  * will remain as flushed as it was. */
 155                 if (!curr->present)
 156                         continue;
 157
 158                 curr->flushed = 0;
 159         }
 160 }
 161
 162 /* In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
 163  * common host process. So this is needed in SKAS0 too.
 164  *
 165  * However, if each thread had a different host process (and this was discussed
 166  * for SMP support) this won't be needed.
 167  *
 168  * And this will not need be used when (and if) we'll add support to the host
 169  * SKAS patch. */
 170
 171 int arch_switch_tls_skas(struct task_struct *from, struct task_struct *to)
 172 {
 173         if (!host_supports_tls)
 174                 return 0;
 175
 176         /* We have no need whatsoever to switch TLS for kernel threads; beyond
 177          * that, that would also result in us calling os_set_thread_area with
 178          * userspace_pid[cpu] == 0, which gives an error. */
 179         if (likely(to->mm))
 180                 return load_TLS(O_FORCE, to);
 181
 182         return 0;
 183 }
 184
 185 static int set_tls_entry(struct task_struct* task, struct user_desc *info,
 186                          int idx, int flushed)
 187 {
 188         struct thread_struct *t = &task->thread;
 189
 190         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 191                 return -EINVAL;
 192
 193         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info;
 194         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1;
 195         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed;
 196
 197         return 0;
 198 }
 199
 200 int arch_copy_tls(struct task_struct *new)
 201 {
 202         struct user_desc info;
 203         int idx, ret = -EFAULT;
 204
 205         if (copy_from_user(&info,
 206                            (void __user *) UPT_ESI(&new->thread.regs.regs),
 207                            sizeof(info)))
 208                 goto out;
 209
 210         ret = -EINVAL;
 211         if (LDT_empty(&info))
 212                 goto out;
 213
 214         idx = info.entry_number;
 215
 216         ret = set_tls_entry(new, &info, idx, 0);
 217 out:
 218         return ret;
 219 }
 220
 221 /* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */
 222 static int get_tls_entry(struct task_struct* task, struct user_desc *info, int idx)
 223 {
 224         struct thread_struct *t = &task->thread;
 225
 226         if (!t->arch.tls_array)
 227                 goto clear;
 228
 229         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 230                 return -EINVAL;
 231
 232         if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present)
 233                 goto clear;
 234
 235         *info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls;
 236
 237 out:
 238         /* Temporary debugging check, to make sure that things have been
 239          * flushed. This could be triggered if load_TLS() failed.
 240          */
 241         if (unlikely(task == current && !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) {
 242                 printk(KERN_ERR "get_tls_entry: task with pid %d got here "
 243                                 "without flushed TLS.", current->pid);
 244         }
 245
 246         return 0;
 247 clear:
 248         /* When the TLS entry has not been set, the values read to user in the
 249          * tls_array are 0 (because it's cleared at boot, see
 250          * arch/i386/kernel/head.S:cpu_gdt_table). Emulate that.
 251          */
 252         clear_user_desc(info);
 253         info->entry_number = idx;
 254         goto out;
 255 }
 256
 257 asmlinkage int sys_set_thread_area(struct user_desc __user *user_desc)
 258 {
 259         struct user_desc info;
 260         int idx, ret;
 261
 262         if (!host_supports_tls)
 263                 return -ENOSYS;
 264
 265         if (copy_from_user(&info, user_desc, sizeof(info)))
 266                 return -EFAULT;
 267
 268         idx = info.entry_number;
 269
 270         if (idx == -1) {
 271                 idx = get_free_idx(current);
 272                 if (idx < 0)
 273                         return idx;
 274                 info.entry_number = idx;
 275                 /* Tell the user which slot we chose for him.*/
 276                 if (put_user(idx, &user_desc->entry_number))
 277                         return -EFAULT;
 278         }
 279
 280         ret = CHOOSE_MODE_PROC(do_set_thread_area_tt, do_set_thread_area_skas, &info);
 281         if (ret)
 282                 return ret;
 283         return set_tls_entry(current, &info, idx, 1);
 284 }
 285
 286 /*
 287  * Perform set_thread_area on behalf of the traced child.
 288  * Note: error handling is not done on the deferred load, and this differ from
 289  * i386. However the only possible error are caused by bugs.
 290  */
 291 int ptrace_set_thread_area(struct task_struct *child, int idx,
 292                 struct user_desc __user *user_desc)
 293 {
 294         struct user_desc info;
 295
 296         if (!host_supports_tls)
 297                 return -EIO;
 298
 299         if (copy_from_user(&info, user_desc, sizeof(info)))
 300                 return -EFAULT;
 301
 302         return set_tls_entry(child, &info, idx, 0);
 303 }
 304
 305 asmlinkage int sys_get_thread_area(struct user_desc __user *user_desc)
 306 {
 307         struct user_desc info;
 308         int idx, ret;
 309
 310         if (!host_supports_tls)
 311                 return -ENOSYS;
 312
 313         if (get_user(idx, &user_desc->entry_number))
 314                 return -EFAULT;
 315
 316         ret = get_tls_entry(current, &info, idx);
 317         if (ret < 0)
 318                 goto out;
 319
 320         if (copy_to_user(user_desc, &info, sizeof(info)))
 321                 ret = -EFAULT;
 322
 323 out:
 324         return ret;
 325 }
 326
 327 /*
 328  * Perform get_thread_area on behalf of the traced child.
 329  */
 330 int ptrace_get_thread_area(struct task_struct *child, int idx,
 331                 struct user_desc __user *user_desc)
 332 {
 333         struct user_desc info;
 334         int ret;
 335
 336         if (!host_supports_tls)
 337                 return -EIO;
 338
 339         ret = get_tls_entry(child, &info, idx);
 340         if (ret < 0)
 341                 goto out;
 342
 343         if (copy_to_user(user_desc, &info, sizeof(info)))
 344                 ret = -EFAULT;
 345 out:
 346         return ret;
 347 }
 348
 349
 350 /* XXX: This part is probably common to i386 and x86-64. Don't create a common
 351  * file for now, do that when implementing x86-64 support.*/
 352 static int __init __setup_host_supports_tls(void)
 353 {
 354         check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
 355         if (host_supports_tls) {
 356                 printk(KERN_INFO "Host TLS support detected\n");
 357                 printk(KERN_INFO "Detected host type: ");
 358                 switch (host_gdt_entry_tls_min) {
 359                         case GDT_ENTRY_TLS_MIN_I386:
 360                                 printk("i386\n");
 361                                 break;
 362                         case GDT_ENTRY_TLS_MIN_X86_64:
 363                                 printk("x86_64\n");
 364                                 break;
 365                 }
 366         } else
 367                 printk(KERN_ERR "  Host TLS support NOT detected! "
 368                                 "TLS support inside UML will not work\n");
 369         return 0;
 370 }
 371
 372 __initcall(__setup_host_supports_tls);