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_set_tls(struct task_struct *new, unsigned long tls) 219 { 220 struct user_desc info; 221 int idx, ret = -EFAULT; 222 223 if (copy_from_user(&info, (void __user *) tls, 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 SYSCALL_DEFINE1(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 SYSCALL_DEFINE1(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); 397