/arch/um/sys-i386/tls.c
C | 396 lines | 245 code | 71 blank | 80 comment | 46 complexity | 8f0b4858488dc1779e77ac84fad8a460 MD5 | raw file
Possible License(s): GPL-2.0, LGPL-2.0, AGPL-1.0
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 */ 18static int host_supports_tls = -1; 19int host_gdt_entry_tls_min; 20 21int 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 37int 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 */ 61static 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 75static 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 90static 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 } 122out: 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 */ 130static 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 */ 155void 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 185int 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 201static 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 216int 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); 233out: 234 return ret; 235} 236 237/* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */ 238static 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 254out: 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; 266clear: 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 277int 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 */ 311int 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 325int 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 343out: 344 return ret; 345} 346 347/* 348 * Perform get_thread_area on behalf of the traced child. 349 */ 350int 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; 365out: 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 */ 373static 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);