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Linux/arch/x86/um/tls_32.c

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  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 

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