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 #include <asm/desc.h> 15 #include <stub-data.h> 16 17 /* 18 * If needed we can detect when it's uninitialized. 19 * 20 * These are initialized in an initcall and unchanged thereafter. 21 */ 22 static int host_supports_tls = -1; 23 int host_gdt_entry_tls_min; 24 25 static int do_set_thread_area(struct task_struct* task, struct user_desc *info) 26 { 27 int ret; 28 29 if (info->entry_number < host_gdt_entry_tls_min || 30 info->entry_number >= host_gdt_entry_tls_min + GDT_ENTRY_TLS_ENTRIES) 31 return -EINVAL; 32 33 if (using_seccomp) { 34 int idx = info->entry_number - host_gdt_entry_tls_min; 35 struct stub_data *data = (void *)task->mm->context.id.stack; 36 37 data->arch_data.tls[idx] = *info; 38 data->arch_data.sync |= BIT(idx); 39 40 return 0; 41 } 42 43 ret = os_set_thread_area(info, task->mm->context.id.pid); 44 45 if (ret) 46 printk(KERN_ERR "PTRACE_SET_THREAD_AREA failed, err = %d, " 47 "index = %d\n", ret, info->entry_number); 48 49 return ret; 50 } 51 52 /* 53 * sys_get_thread_area: get a yet unused TLS descriptor index. 54 * XXX: Consider leaving one free slot for glibc usage at first place. This must 55 * be done here (and by changing GDT_ENTRY_TLS_* macros) and nowhere else. 56 * 57 * Also, this must be tested when compiling in SKAS mode with dynamic linking 58 * and running against NPTL. 59 */ 60 static int get_free_idx(struct task_struct* task) 61 { 62 struct thread_struct *t = &task->thread; 63 int idx; 64 65 for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++) 66 if (!t->arch.tls_array[idx].present) 67 return idx + GDT_ENTRY_TLS_MIN; 68 return -ESRCH; 69 } 70 71 static inline void clear_user_desc(struct user_desc* info) 72 { 73 /* Postcondition: LDT_empty(info) returns true. */ 74 memset(info, 0, sizeof(*info)); 75 76 /* 77 * Check the LDT_empty or the i386 sys_get_thread_area code - we obtain 78 * indeed an empty user_desc. 79 */ 80 info->read_exec_only = 1; 81 info->seg_not_present = 1; 82 } 83 84 #define O_FORCE 1 85 86 static int load_TLS(int flags, struct task_struct *to) 87 { 88 int ret = 0; 89 int idx; 90 91 for (idx = GDT_ENTRY_TLS_MIN; idx < GDT_ENTRY_TLS_MAX; idx++) { 92 struct uml_tls_struct* curr = 93 &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN]; 94 95 /* 96 * Actually, now if it wasn't flushed it gets cleared and 97 * flushed to the host, which will clear it. 98 */ 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(current, &curr->tls); 113 if (ret) 114 goto out; 115 116 curr->flushed = 1; 117 } 118 out: 119 return ret; 120 } 121 122 /* 123 * Verify if we need to do a flush for the new process, i.e. if there are any 124 * present desc's, only if they haven't been flushed. 125 */ 126 static inline int needs_TLS_update(struct task_struct *task) 127 { 128 int i; 129 int ret = 0; 130 131 for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) { 132 struct uml_tls_struct* curr = 133 &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN]; 134 135 /* 136 * Can't test curr->present, we may need to clear a descriptor 137 * which had a value. 138 */ 139 if (curr->flushed) 140 continue; 141 ret = 1; 142 break; 143 } 144 return ret; 145 } 146 147 /* 148 * On a newly forked process, the TLS descriptors haven't yet been flushed. So 149 * we mark them as such and the first switch_to will do the job. 150 */ 151 void clear_flushed_tls(struct task_struct *task) 152 { 153 int i; 154 155 for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) { 156 struct uml_tls_struct* curr = 157 &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN]; 158 159 /* 160 * Still correct to do this, if it wasn't present on the host it 161 * will remain as flushed as it was. 162 */ 163 if (!curr->present) 164 continue; 165 166 curr->flushed = 0; 167 } 168 } 169 170 /* 171 * In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a 172 * common host process. So this is needed in SKAS0 too. 173 * 174 * However, if each thread had a different host process (and this was discussed 175 * for SMP support) this won't be needed. 176 * 177 * And this will not need be used when (and if) we'll add support to the host 178 * SKAS patch. 179 */ 180 181 int arch_switch_tls(struct task_struct *to) 182 { 183 if (!host_supports_tls) 184 return 0; 185 186 /* 187 * We have no need whatsoever to switch TLS for kernel threads; beyond 188 * that, that would also result in us calling os_set_thread_area with 189 * userspace_pid[cpu] == 0, which gives an error. 190 */ 191 if (likely(to->mm)) 192 return load_TLS(O_FORCE, to); 193 194 return 0; 195 } 196 197 static int set_tls_entry(struct task_struct* task, struct user_desc *info, 198 int idx, int flushed) 199 { 200 struct thread_struct *t = &task->thread; 201 202 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX) 203 return -EINVAL; 204 205 t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info; 206 t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1; 207 t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed; 208 209 return 0; 210 } 211 212 int arch_set_tls(struct task_struct *new, unsigned long tls) 213 { 214 struct user_desc info; 215 int idx, ret = -EFAULT; 216 217 if (copy_from_user(&info, (void __user *) tls, sizeof(info))) 218 goto out; 219 220 ret = -EINVAL; 221 if (LDT_empty(&info)) 222 goto out; 223 224 idx = info.entry_number; 225 226 ret = set_tls_entry(new, &info, idx, 0); 227 out: 228 return ret; 229 } 230 231 static int get_tls_entry(struct task_struct *task, struct user_desc *info, 232 int idx) 233 { 234 struct thread_struct *t = &task->thread; 235 236 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX) 237 return -EINVAL; 238 239 if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present) 240 goto clear; 241 242 *info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls; 243 244 out: 245 /* 246 * Temporary debugging check, to make sure that things have been 247 * flushed. This could be triggered if load_TLS() failed. 248 */ 249 if (unlikely(task == current && 250 !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) { 251 printk(KERN_ERR "get_tls_entry: task with pid %d got here " 252 "without flushed TLS.", current->pid); 253 } 254 255 return 0; 256 clear: 257 /* 258 * When the TLS entry has not been set, the values read to user in the 259 * tls_array are 0 (because it's cleared at boot, see 260 * arch/i386/kernel/head.S:cpu_gdt_table). Emulate that. 261 */ 262 clear_user_desc(info); 263 info->entry_number = idx; 264 goto out; 265 } 266 267 SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, user_desc) 268 { 269 struct user_desc info; 270 int idx, ret; 271 272 if (!host_supports_tls) 273 return -ENOSYS; 274 275 if (copy_from_user(&info, user_desc, sizeof(info))) 276 return -EFAULT; 277 278 idx = info.entry_number; 279 280 if (idx == -1) { 281 idx = get_free_idx(current); 282 if (idx < 0) 283 return idx; 284 info.entry_number = idx; 285 /* Tell the user which slot we chose for him.*/ 286 if (put_user(idx, &user_desc->entry_number)) 287 return -EFAULT; 288 } 289 290 ret = do_set_thread_area(current, &info); 291 if (ret) 292 return ret; 293 return set_tls_entry(current, &info, idx, 1); 294 } 295 296 /* 297 * Perform set_thread_area on behalf of the traced child. 298 * Note: error handling is not done on the deferred load, and this differ from 299 * i386. However the only possible error are caused by bugs. 300 */ 301 int ptrace_set_thread_area(struct task_struct *child, int idx, 302 struct user_desc __user *user_desc) 303 { 304 struct user_desc info; 305 306 if (!host_supports_tls) 307 return -EIO; 308 309 if (copy_from_user(&info, user_desc, sizeof(info))) 310 return -EFAULT; 311 312 return set_tls_entry(child, &info, idx, 0); 313 } 314 315 SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, user_desc) 316 { 317 struct user_desc info; 318 int idx, ret; 319 320 if (!host_supports_tls) 321 return -ENOSYS; 322 323 if (get_user(idx, &user_desc->entry_number)) 324 return -EFAULT; 325 326 ret = get_tls_entry(current, &info, idx); 327 if (ret < 0) 328 goto out; 329 330 if (copy_to_user(user_desc, &info, sizeof(info))) 331 ret = -EFAULT; 332 333 out: 334 return ret; 335 } 336 337 /* 338 * Perform get_thread_area on behalf of the traced child. 339 */ 340 int ptrace_get_thread_area(struct task_struct *child, int idx, 341 struct user_desc __user *user_desc) 342 { 343 struct user_desc info; 344 int ret; 345 346 if (!host_supports_tls) 347 return -EIO; 348 349 ret = get_tls_entry(child, &info, idx); 350 if (ret < 0) 351 goto out; 352 353 if (copy_to_user(user_desc, &info, sizeof(info))) 354 ret = -EFAULT; 355 out: 356 return ret; 357 } 358 359 /* 360 * This code is really i386-only, but it detects and logs x86_64 GDT indexes 361 * if a 32-bit UML is running on a 64-bit host. 362 */ 363 static int __init __setup_host_supports_tls(void) 364 { 365 check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min); 366 if (host_supports_tls) { 367 printk(KERN_INFO "Host TLS support detected\n"); 368 printk(KERN_INFO "Detected host type: "); 369 switch (host_gdt_entry_tls_min) { 370 case GDT_ENTRY_TLS_MIN_I386: 371 printk(KERN_CONT "i386"); 372 break; 373 case GDT_ENTRY_TLS_MIN_X86_64: 374 printk(KERN_CONT "x86_64"); 375 break; 376 } 377 printk(KERN_CONT " (GDT indexes %d to %d)\n", 378 host_gdt_entry_tls_min, 379 host_gdt_entry_tls_min + GDT_ENTRY_TLS_ENTRIES); 380 } else 381 printk(KERN_ERR " Host TLS support NOT detected! " 382 "TLS support inside UML will not work\n"); 383 return 0; 384 } 385 386 __initcall(__setup_host_supports_tls); 387