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 <linux/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 if (!t->arch.tls_array) 69 return GDT_ENTRY_TLS_MIN; 70 71 for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++) 72 if (!t->arch.tls_array[idx].present) 73 return idx + GDT_ENTRY_TLS_MIN; 74 return -ESRCH; 75 } 76 77 static inline void clear_user_desc(struct user_desc* info) 78 { 79 /* Postcondition: LDT_empty(info) returns true. */ 80 memset(info, 0, sizeof(*info)); 81 82 /* 83 * Check the LDT_empty or the i386 sys_get_thread_area code - we obtain 84 * indeed an empty user_desc. 85 */ 86 info->read_exec_only = 1; 87 info->seg_not_present = 1; 88 } 89 90 #define O_FORCE 1 91 92 static int load_TLS(int flags, struct task_struct *to) 93 { 94 int ret = 0; 95 int idx; 96 97 for (idx = GDT_ENTRY_TLS_MIN; idx < GDT_ENTRY_TLS_MAX; idx++) { 98 struct uml_tls_struct* curr = 99 &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN]; 100 101 /* 102 * Actually, now if it wasn't flushed it gets cleared and 103 * flushed to the host, which will clear it. 104 */ 105 if (!curr->present) { 106 if (!curr->flushed) { 107 clear_user_desc(&curr->tls); 108 curr->tls.entry_number = idx; 109 } else { 110 WARN_ON(!LDT_empty(&curr->tls)); 111 continue; 112 } 113 } 114 115 if (!(flags & O_FORCE) && curr->flushed) 116 continue; 117 118 ret = do_set_thread_area(&curr->tls); 119 if (ret) 120 goto out; 121 122 curr->flushed = 1; 123 } 124 out: 125 return ret; 126 } 127 128 /* 129 * Verify if we need to do a flush for the new process, i.e. if there are any 130 * present desc's, only if they haven't been flushed. 131 */ 132 static inline int needs_TLS_update(struct task_struct *task) 133 { 134 int i; 135 int ret = 0; 136 137 for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) { 138 struct uml_tls_struct* curr = 139 &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN]; 140 141 /* 142 * Can't test curr->present, we may need to clear a descriptor 143 * which had a value. 144 */ 145 if (curr->flushed) 146 continue; 147 ret = 1; 148 break; 149 } 150 return ret; 151 } 152 153 /* 154 * On a newly forked process, the TLS descriptors haven't yet been flushed. So 155 * we mark them as such and the first switch_to will do the job. 156 */ 157 void clear_flushed_tls(struct task_struct *task) 158 { 159 int i; 160 161 for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) { 162 struct uml_tls_struct* curr = 163 &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN]; 164 165 /* 166 * Still correct to do this, if it wasn't present on the host it 167 * will remain as flushed as it was. 168 */ 169 if (!curr->present) 170 continue; 171 172 curr->flushed = 0; 173 } 174 } 175 176 /* 177 * In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a 178 * common host process. So this is needed in SKAS0 too. 179 * 180 * However, if each thread had a different host process (and this was discussed 181 * for SMP support) this won't be needed. 182 * 183 * And this will not need be used when (and if) we'll add support to the host 184 * SKAS patch. 185 */ 186 187 int arch_switch_tls(struct task_struct *to) 188 { 189 if (!host_supports_tls) 190 return 0; 191 192 /* 193 * We have no need whatsoever to switch TLS for kernel threads; beyond 194 * that, that would also result in us calling os_set_thread_area with 195 * userspace_pid[cpu] == 0, which gives an error. 196 */ 197 if (likely(to->mm)) 198 return load_TLS(O_FORCE, to); 199 200 return 0; 201 } 202 203 static int set_tls_entry(struct task_struct* task, struct user_desc *info, 204 int idx, int flushed) 205 { 206 struct thread_struct *t = &task->thread; 207 208 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX) 209 return -EINVAL; 210 211 t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info; 212 t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1; 213 t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed; 214 215 return 0; 216 } 217 218 int arch_copy_tls(struct task_struct *new) 219 { 220 struct user_desc info; 221 int idx, ret = -EFAULT; 222 223 if (copy_from_user(&info, 224 (void __user *) UPT_SI(&new->thread.regs.regs), 225 sizeof(info))) 226 goto out; 227 228 ret = -EINVAL; 229 if (LDT_empty(&info)) 230 goto out; 231 232 idx = info.entry_number; 233 234 ret = set_tls_entry(new, &info, idx, 0); 235 out: 236 return ret; 237 } 238 239 /* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */ 240 static int get_tls_entry(struct task_struct *task, struct user_desc *info, 241 int idx) 242 { 243 struct thread_struct *t = &task->thread; 244 245 if (!t->arch.tls_array) 246 goto clear; 247 248 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX) 249 return -EINVAL; 250 251 if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present) 252 goto clear; 253 254 *info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls; 255 256 out: 257 /* 258 * Temporary debugging check, to make sure that things have been 259 * flushed. This could be triggered if load_TLS() failed. 260 */ 261 if (unlikely(task == current && 262 !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) { 263 printk(KERN_ERR "get_tls_entry: task with pid %d got here " 264 "without flushed TLS.", current->pid); 265 } 266 267 return 0; 268 clear: 269 /* 270 * When the TLS entry has not been set, the values read to user in the 271 * tls_array are 0 (because it's cleared at boot, see 272 * arch/i386/kernel/head.S:cpu_gdt_table). Emulate that. 273 */ 274 clear_user_desc(info); 275 info->entry_number = idx; 276 goto out; 277 } 278 279 SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, user_desc) 280 { 281 struct user_desc info; 282 int idx, ret; 283 284 if (!host_supports_tls) 285 return -ENOSYS; 286 287 if (copy_from_user(&info, user_desc, sizeof(info))) 288 return -EFAULT; 289 290 idx = info.entry_number; 291 292 if (idx == -1) { 293 idx = get_free_idx(current); 294 if (idx < 0) 295 return idx; 296 info.entry_number = idx; 297 /* Tell the user which slot we chose for him.*/ 298 if (put_user(idx, &user_desc->entry_number)) 299 return -EFAULT; 300 } 301 302 ret = do_set_thread_area(&info); 303 if (ret) 304 return ret; 305 return set_tls_entry(current, &info, idx, 1); 306 } 307 308 /* 309 * Perform set_thread_area on behalf of the traced child. 310 * Note: error handling is not done on the deferred load, and this differ from 311 * i386. However the only possible error are caused by bugs. 312 */ 313 int ptrace_set_thread_area(struct task_struct *child, int idx, 314 struct user_desc __user *user_desc) 315 { 316 struct user_desc info; 317 318 if (!host_supports_tls) 319 return -EIO; 320 321 if (copy_from_user(&info, user_desc, sizeof(info))) 322 return -EFAULT; 323 324 return set_tls_entry(child, &info, idx, 0); 325 } 326 327 SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, user_desc) 328 { 329 struct user_desc info; 330 int idx, ret; 331 332 if (!host_supports_tls) 333 return -ENOSYS; 334 335 if (get_user(idx, &user_desc->entry_number)) 336 return -EFAULT; 337 338 ret = get_tls_entry(current, &info, idx); 339 if (ret < 0) 340 goto out; 341 342 if (copy_to_user(user_desc, &info, sizeof(info))) 343 ret = -EFAULT; 344 345 out: 346 return ret; 347 } 348 349 /* 350 * Perform get_thread_area on behalf of the traced child. 351 */ 352 int ptrace_get_thread_area(struct task_struct *child, int idx, 353 struct user_desc __user *user_desc) 354 { 355 struct user_desc info; 356 int ret; 357 358 if (!host_supports_tls) 359 return -EIO; 360 361 ret = get_tls_entry(child, &info, idx); 362 if (ret < 0) 363 goto out; 364 365 if (copy_to_user(user_desc, &info, sizeof(info))) 366 ret = -EFAULT; 367 out: 368 return ret; 369 } 370 371 /* 372 * This code is really i386-only, but it detects and logs x86_64 GDT indexes 373 * if a 32-bit UML is running on a 64-bit host. 374 */ 375 static int __init __setup_host_supports_tls(void) 376 { 377 check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min); 378 if (host_supports_tls) { 379 printk(KERN_INFO "Host TLS support detected\n"); 380 printk(KERN_INFO "Detected host type: "); 381 switch (host_gdt_entry_tls_min) { 382 case GDT_ENTRY_TLS_MIN_I386: 383 printk(KERN_CONT "i386"); 384 break; 385 case GDT_ENTRY_TLS_MIN_X86_64: 386 printk(KERN_CONT "x86_64"); 387 break; 388 } 389 printk(KERN_CONT " (GDT indexes %d to %d)\n", 390 host_gdt_entry_tls_min, 391 host_gdt_entry_tls_min + GDT_ENTRY_TLS_ENTRIES); 392 } else 393 printk(KERN_ERR " Host TLS support NOT detected! " 394 "TLS support inside UML will not work\n"); 395 return 0; 396 } 397 398 __initcall(__setup_host_supports_tls); 399