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 static 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 /* 40 * sys_get_thread_area: get a yet unused TLS descriptor index. 41 * XXX: Consider leaving one free slot for glibc usage at first place. This must 42 * be done here (and by changing GDT_ENTRY_TLS_* macros) and nowhere else. 43 * 44 * Also, this must be tested when compiling in SKAS mode with dynamic linking 45 * and running against NPTL. 46 */ 47 static int get_free_idx(struct task_struct* task) 48 { 49 struct thread_struct *t = &task->thread; 50 int idx; 51 52 for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++) 53 if (!t->arch.tls_array[idx].present) 54 return idx + GDT_ENTRY_TLS_MIN; 55 return -ESRCH; 56 } 57 58 static inline void clear_user_desc(struct user_desc* info) 59 { 60 /* Postcondition: LDT_empty(info) returns true. */ 61 memset(info, 0, sizeof(*info)); 62 63 /* 64 * Check the LDT_empty or the i386 sys_get_thread_area code - we obtain 65 * indeed an empty user_desc. 66 */ 67 info->read_exec_only = 1; 68 info->seg_not_present = 1; 69 } 70 71 #define O_FORCE 1 72 73 static int load_TLS(int flags, struct task_struct *to) 74 { 75 int ret = 0; 76 int idx; 77 78 for (idx = GDT_ENTRY_TLS_MIN; idx < GDT_ENTRY_TLS_MAX; idx++) { 79 struct uml_tls_struct* curr = 80 &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN]; 81 82 /* 83 * Actually, now if it wasn't flushed it gets cleared and 84 * flushed to the host, which will clear it. 85 */ 86 if (!curr->present) { 87 if (!curr->flushed) { 88 clear_user_desc(&curr->tls); 89 curr->tls.entry_number = idx; 90 } else { 91 WARN_ON(!LDT_empty(&curr->tls)); 92 continue; 93 } 94 } 95 96 if (!(flags & O_FORCE) && curr->flushed) 97 continue; 98 99 ret = do_set_thread_area(&curr->tls); 100 if (ret) 101 goto out; 102 103 curr->flushed = 1; 104 } 105 out: 106 return ret; 107 } 108 109 /* 110 * Verify if we need to do a flush for the new process, i.e. if there are any 111 * present desc's, only if they haven't been flushed. 112 */ 113 static inline int needs_TLS_update(struct task_struct *task) 114 { 115 int i; 116 int ret = 0; 117 118 for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) { 119 struct uml_tls_struct* curr = 120 &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN]; 121 122 /* 123 * Can't test curr->present, we may need to clear a descriptor 124 * which had a value. 125 */ 126 if (curr->flushed) 127 continue; 128 ret = 1; 129 break; 130 } 131 return ret; 132 } 133 134 /* 135 * On a newly forked process, the TLS descriptors haven't yet been flushed. So 136 * we mark them as such and the first switch_to will do the job. 137 */ 138 void clear_flushed_tls(struct task_struct *task) 139 { 140 int i; 141 142 for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) { 143 struct uml_tls_struct* curr = 144 &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN]; 145 146 /* 147 * Still correct to do this, if it wasn't present on the host it 148 * will remain as flushed as it was. 149 */ 150 if (!curr->present) 151 continue; 152 153 curr->flushed = 0; 154 } 155 } 156 157 /* 158 * In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a 159 * common host process. So this is needed in SKAS0 too. 160 * 161 * However, if each thread had a different host process (and this was discussed 162 * for SMP support) this won't be needed. 163 * 164 * And this will not need be used when (and if) we'll add support to the host 165 * SKAS patch. 166 */ 167 168 int arch_switch_tls(struct task_struct *to) 169 { 170 if (!host_supports_tls) 171 return 0; 172 173 /* 174 * We have no need whatsoever to switch TLS for kernel threads; beyond 175 * that, that would also result in us calling os_set_thread_area with 176 * userspace_pid[cpu] == 0, which gives an error. 177 */ 178 if (likely(to->mm)) 179 return load_TLS(O_FORCE, to); 180 181 return 0; 182 } 183 184 static int set_tls_entry(struct task_struct* task, struct user_desc *info, 185 int idx, int flushed) 186 { 187 struct thread_struct *t = &task->thread; 188 189 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX) 190 return -EINVAL; 191 192 t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info; 193 t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1; 194 t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed; 195 196 return 0; 197 } 198 199 int arch_set_tls(struct task_struct *new, unsigned long tls) 200 { 201 struct user_desc info; 202 int idx, ret = -EFAULT; 203 204 if (copy_from_user(&info, (void __user *) tls, 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 static int get_tls_entry(struct task_struct *task, struct user_desc *info, 219 int idx) 220 { 221 struct thread_struct *t = &task->thread; 222 223 if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX) 224 return -EINVAL; 225 226 if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present) 227 goto clear; 228 229 *info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls; 230 231 out: 232 /* 233 * Temporary debugging check, to make sure that things have been 234 * flushed. This could be triggered if load_TLS() failed. 235 */ 236 if (unlikely(task == current && 237 !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) { 238 printk(KERN_ERR "get_tls_entry: task with pid %d got here " 239 "without flushed TLS.", current->pid); 240 } 241 242 return 0; 243 clear: 244 /* 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 SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, user_desc) 255 { 256 struct user_desc info; 257 int idx, ret; 258 259 if (!host_supports_tls) 260 return -ENOSYS; 261 262 if (copy_from_user(&info, user_desc, sizeof(info))) 263 return -EFAULT; 264 265 idx = info.entry_number; 266 267 if (idx == -1) { 268 idx = get_free_idx(current); 269 if (idx < 0) 270 return idx; 271 info.entry_number = idx; 272 /* Tell the user which slot we chose for him.*/ 273 if (put_user(idx, &user_desc->entry_number)) 274 return -EFAULT; 275 } 276 277 ret = do_set_thread_area(&info); 278 if (ret) 279 return ret; 280 return set_tls_entry(current, &info, idx, 1); 281 } 282 283 /* 284 * Perform set_thread_area on behalf of the traced child. 285 * Note: error handling is not done on the deferred load, and this differ from 286 * i386. However the only possible error are caused by bugs. 287 */ 288 int ptrace_set_thread_area(struct task_struct *child, int idx, 289 struct user_desc __user *user_desc) 290 { 291 struct user_desc info; 292 293 if (!host_supports_tls) 294 return -EIO; 295 296 if (copy_from_user(&info, user_desc, sizeof(info))) 297 return -EFAULT; 298 299 return set_tls_entry(child, &info, idx, 0); 300 } 301 302 SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, user_desc) 303 { 304 struct user_desc info; 305 int idx, ret; 306 307 if (!host_supports_tls) 308 return -ENOSYS; 309 310 if (get_user(idx, &user_desc->entry_number)) 311 return -EFAULT; 312 313 ret = get_tls_entry(current, &info, idx); 314 if (ret < 0) 315 goto out; 316 317 if (copy_to_user(user_desc, &info, sizeof(info))) 318 ret = -EFAULT; 319 320 out: 321 return ret; 322 } 323 324 /* 325 * Perform get_thread_area on behalf of the traced child. 326 */ 327 int ptrace_get_thread_area(struct task_struct *child, int idx, 328 struct user_desc __user *user_desc) 329 { 330 struct user_desc info; 331 int ret; 332 333 if (!host_supports_tls) 334 return -EIO; 335 336 ret = get_tls_entry(child, &info, idx); 337 if (ret < 0) 338 goto out; 339 340 if (copy_to_user(user_desc, &info, sizeof(info))) 341 ret = -EFAULT; 342 out: 343 return ret; 344 } 345 346 /* 347 * This code is really i386-only, but it detects and logs x86_64 GDT indexes 348 * if a 32-bit UML is running on a 64-bit host. 349 */ 350 static int __init __setup_host_supports_tls(void) 351 { 352 check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min); 353 if (host_supports_tls) { 354 printk(KERN_INFO "Host TLS support detected\n"); 355 printk(KERN_INFO "Detected host type: "); 356 switch (host_gdt_entry_tls_min) { 357 case GDT_ENTRY_TLS_MIN_I386: 358 printk(KERN_CONT "i386"); 359 break; 360 case GDT_ENTRY_TLS_MIN_X86_64: 361 printk(KERN_CONT "x86_64"); 362 break; 363 } 364 printk(KERN_CONT " (GDT indexes %d to %d)\n", 365 host_gdt_entry_tls_min, 366 host_gdt_entry_tls_min + GDT_ENTRY_TLS_ENTRIES); 367 } else 368 printk(KERN_ERR " Host TLS support NOT detected! " 369 "TLS support inside UML will not work\n"); 370 return 0; 371 } 372 373 __initcall(__setup_host_supports_tls); 374