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/config.h"
   7 #include "linux/kernel.h"
   8 #include "linux/sched.h"
   9 #include "linux/slab.h"
  10 #include "linux/types.h"
  11 #include "asm/uaccess.h"
  12 #include "asm/ptrace.h"
  13 #include "asm/segment.h"
  14 #include "asm/smp.h"
  15 #include "asm/desc.h"
  16 #include "choose-mode.h"
  17 #include "kern.h"
  18 #include "kern_util.h"
  19 #include "mode_kern.h"
  20 #include "os.h"
  21 #include "mode.h"
  22
  23 #ifdef CONFIG_MODE_SKAS
  24 #include "skas.h"
  25 #endif
  26
  27 #ifdef CONFIG_MODE_SKAS
  28 int do_set_thread_area_skas(struct user_desc *info)
  29 {
  30         int ret;
  31         u32 cpu;
  32
  33         cpu = get_cpu();
  34         ret = os_set_thread_area(info, userspace_pid[cpu]);
  35         put_cpu();
  36         return ret;
  37 }
  38
  39 int do_get_thread_area_skas(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         return ret;
  48 }
  49 #endif
  50
  51 /*
  52  * sys_get_thread_area: get a yet unused TLS descriptor index.
  53  * XXX: Consider leaving one free slot for glibc usage at first place. This must
  54  * be done here (and by changing GDT_ENTRY_TLS_* macros) and nowhere else.
  55  *
  56  * Also, this must be tested when compiling in SKAS mode with dinamic linking
  57  * and running against NPTL.
  58  */
  59 static int get_free_idx(struct task_struct* task)
  60 {
  61         struct thread_struct *t = &task->thread;
  62         int idx;
  63
  64         if (!t->arch.tls_array)
  65                 return GDT_ENTRY_TLS_MIN;
  66
  67         for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
  68                 if (!t->arch.tls_array[idx].present)
  69                         return idx + GDT_ENTRY_TLS_MIN;
  70         return -ESRCH;
  71 }
  72
  73 static inline void clear_user_desc(struct user_desc* info)
  74 {
  75         /* Postcondition: LDT_empty(info) returns true. */
  76         memset(info, 0, sizeof(*info));
  77
  78         /* Check the LDT_empty or the i386 sys_get_thread_area code - we obtain
  79          * indeed an empty user_desc.
  80          */
  81         info->read_exec_only = 1;
  82         info->seg_not_present = 1;
  83 }
  84
  85 #define O_FORCE 1
  86
  87 static int load_TLS(int flags, struct task_struct *to)
  88 {
  89         int ret = 0;
  90         int idx;
  91
  92         for (idx = GDT_ENTRY_TLS_MIN; idx < GDT_ENTRY_TLS_MAX; idx++) {
  93                 struct uml_tls_struct* curr = &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];
  94
  95                 /* Actually, now if it wasn't flushed it gets cleared and
  96                  * flushed to the host, which will clear it.*/
  97                 if (!curr->present) {
  98                         if (!curr->flushed) {
  99                                 clear_user_desc(&curr->tls);
 100                                 curr->tls.entry_number = idx;
 101                         } else {
 102                                 WARN_ON(!LDT_empty(&curr->tls));
 103                                 continue;
 104                         }
 105                 }
 106
 107                 if (!(flags & O_FORCE) && curr->flushed)
 108                         continue;
 109
 110                 ret = do_set_thread_area(&curr->tls);
 111                 if (ret)
 112                         goto out;
 113
 114                 curr->flushed = 1;
 115         }
 116 out:
 117         return ret;
 118 }
 119
 120 /* Verify if we need to do a flush for the new process, i.e. if there are any
 121  * present desc's, only if they haven't been flushed.
 122  */
 123 static inline int needs_TLS_update(struct task_struct *task)
 124 {
 125         int i;
 126         int ret = 0;
 127
 128         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 129                 struct uml_tls_struct* curr = &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 130
 131                 /* Can't test curr->present, we may need to clear a descriptor
 132                  * which had a value. */
 133                 if (curr->flushed)
 134                         continue;
 135                 ret = 1;
 136                 break;
 137         }
 138         return ret;
 139 }
 140
 141 /* On a newly forked process, the TLS descriptors haven't yet been flushed. So
 142  * we mark them as such and the first switch_to will do the job.
 143  */
 144 void clear_flushed_tls(struct task_struct *task)
 145 {
 146         int i;
 147
 148         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
 149                 struct uml_tls_struct* curr = &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
 150
 151                 /* Still correct to do this, if it wasn't present on the host it
 152                  * will remain as flushed as it was. */
 153                 if (!curr->present)
 154                         continue;
 155
 156                 curr->flushed = 0;
 157         }
 158 }
 159
 160 /* This in SKAS0 does not need to be used, since we have different host
 161  * processes. Nor will this need to be used when we'll add support to the host
 162  * SKAS patch. */
 163 int arch_switch_tls_skas(struct task_struct *from, struct task_struct *to)
 164 {
 165         /* We have no need whatsoever to switch TLS for kernel threads; beyond
 166          * that, that would also result in us calling os_set_thread_area with
 167          * userspace_pid[cpu] == 0, which gives an error. */
 168         if (likely(to->mm))
 169                 return load_TLS(O_FORCE, to);
 170
 171         return 0;
 172 }
 173
 174 int arch_switch_tls_tt(struct task_struct *from, struct task_struct *to)
 175 {
 176         if (needs_TLS_update(to))
 177                 return load_TLS(0, to);
 178
 179         return 0;
 180 }
 181
 182 static int set_tls_entry(struct task_struct* task, struct user_desc *info,
 183                          int idx, int flushed)
 184 {
 185         struct thread_struct *t = &task->thread;
 186
 187         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 188                 return -EINVAL;
 189
 190         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info;
 191         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1;
 192         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed;
 193
 194         return 0;
 195 }
 196
 197 int arch_copy_tls(struct task_struct *new)
 198 {
 199         struct user_desc info;
 200         int idx, ret = -EFAULT;
 201
 202         if (copy_from_user(&info,
 203                            (void __user *) UPT_ESI(&new->thread.regs.regs),
 204                            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 /* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */
 219 static int get_tls_entry(struct task_struct* task, struct user_desc *info, int idx)
 220 {
 221         struct thread_struct *t = &task->thread;
 222
 223         if (!t->arch.tls_array)
 224                 goto clear;
 225
 226         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
 227                 return -EINVAL;
 228
 229         if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present)
 230                 goto clear;
 231
 232         *info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls;
 233
 234 out:
 235         /* Temporary debugging check, to make sure that things have been
 236          * flushed. This could be triggered if load_TLS() failed.
 237          */
 238         if (unlikely(task == current && !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) {
 239                 printk(KERN_ERR "get_tls_entry: task with pid %d got here "
 240                                 "without flushed TLS.", current->pid);
 241         }
 242
 243         return 0;
 244 clear:
 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 asmlinkage int sys_set_thread_area(struct user_desc __user *user_desc)
 255 {
 256         struct user_desc info;
 257         int idx, ret;
 258
 259         if (copy_from_user(&info, user_desc, sizeof(info)))
 260                 return -EFAULT;
 261
 262         idx = info.entry_number;
 263
 264         if (idx == -1) {
 265                 idx = get_free_idx(current);
 266                 if (idx < 0)
 267                         return idx;
 268                 info.entry_number = idx;
 269                 /* Tell the user which slot we chose for him.*/
 270                 if (put_user(idx, &user_desc->entry_number))
 271                         return -EFAULT;
 272         }
 273
 274         ret = CHOOSE_MODE_PROC(do_set_thread_area_tt, do_set_thread_area_skas, &info);
 275         if (ret)
 276                 return ret;
 277         return set_tls_entry(current, &info, idx, 1);
 278 }
 279
 280 /*
 281  * Perform set_thread_area on behalf of the traced child.
 282  * Note: error handling is not done on the deferred load, and this differ from
 283  * i386. However the only possible error are caused by bugs.
 284  */
 285 int ptrace_set_thread_area(struct task_struct *child, int idx,
 286                 struct user_desc __user *user_desc)
 287 {
 288         struct user_desc info;
 289
 290         if (copy_from_user(&info, user_desc, sizeof(info)))
 291                 return -EFAULT;
 292
 293         return set_tls_entry(child, &info, idx, 0);
 294 }
 295
 296 asmlinkage int sys_get_thread_area(struct user_desc __user *user_desc)
 297 {
 298         struct user_desc info;
 299         int idx, ret;
 300
 301         if (get_user(idx, &user_desc->entry_number))
 302                 return -EFAULT;
 303
 304         ret = get_tls_entry(current, &info, idx);
 305         if (ret < 0)
 306                 goto out;
 307
 308         if (copy_to_user(user_desc, &info, sizeof(info)))
 309                 ret = -EFAULT;
 310
 311 out:
 312         return ret;
 313 }
 314
 315 /*
 316  * Perform get_thread_area on behalf of the traced child.
 317  */
 318 int ptrace_get_thread_area(struct task_struct *child, int idx,
 319                 struct user_desc __user *user_desc)
 320 {
 321         struct user_desc info;
 322         int ret;
 323
 324         ret = get_tls_entry(child, &info, idx);
 325         if (ret < 0)
 326                 goto out;
 327
 328         if (copy_to_user(user_desc, &info, sizeof(info)))
 329                 ret = -EFAULT;
 330 out:
 331         return ret;
 332 }
 333