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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 <asm/uaccess.h>
 10 #include <os.h>
 11 #include <skas.h>
 12 #include <sysdep/tls.h>
 13 
 14 /*
 15  * If needed we can detect when it's uninitialized.
 16  *
 17  * These are initialized in an initcall and unchanged thereafter.
 18  */
 19 static int host_supports_tls = -1;
 20 int host_gdt_entry_tls_min;
 21 
 22 int do_set_thread_area(struct user_desc *info)
 23 {
 24         int ret;
 25         u32 cpu;
 26 
 27         cpu = get_cpu();
 28         ret = os_set_thread_area(info, userspace_pid[cpu]);
 29         put_cpu();
 30 
 31         if (ret)
 32                 printk(KERN_ERR "PTRACE_SET_THREAD_AREA failed, err = %d, "
 33                        "index = %d\n", ret, info->entry_number);
 34 
 35         return ret;
 36 }
 37 
 38 int do_get_thread_area(struct user_desc *info)
 39 {
 40         int ret;
 41         u32 cpu;
 42 
 43         cpu = get_cpu();
 44         ret = os_get_thread_area(info, userspace_pid[cpu]);
 45         put_cpu();
 46 
 47         if (ret)
 48                 printk(KERN_ERR "PTRACE_GET_THREAD_AREA failed, err = %d, "
 49                        "index = %d\n", ret, info->entry_number);
 50 
 51         return ret;
 52 }
 53 
 54 /*
 55  * sys_get_thread_area: get a yet unused TLS descriptor index.
 56  * XXX: Consider leaving one free slot for glibc usage at first place. This must
 57  * be done here (and by changing GDT_ENTRY_TLS_* macros) and nowhere else.
 58  *
 59  * Also, this must be tested when compiling in SKAS mode with dynamic linking
 60  * and running against NPTL.
 61  */
 62 static int get_free_idx(struct task_struct* task)
 63 {
 64         struct thread_struct *t = &task->thread;
 65         int idx;
 66 
 67         if (!t->arch.tls_array)
 68                 return GDT_ENTRY_TLS_MIN;
 69 
 70         for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
 71                 if (!t->arch.tls_array[idx].present)
 72                         return idx + GDT_ENTRY_TLS_MIN;
 73         return -ESRCH;
 74 }
 75 
 76 static inline void clear_user_desc(struct user_desc* info)
 77 {
 78         /* Postcondition: LDT_empty(info) returns true. */
 79         memset(info, 0, sizeof(*info));
 80 
 81         /*
 82          * Check the LDT_empty or the i386 sys_get_thread_area code - we obtain
 83          * indeed an empty user_desc.
 84          */
 85         info->read_exec_only = 1;
 86         info->seg_not_present = 1;
 87 }
 88 
 89 #define O_FORCE 1
 90 
 91 static int load_TLS(int flags, struct task_struct *to)
 92 {
 93         int ret = 0;
 94         int idx;
 95 
 96         for (idx = GDT_ENTRY_TLS_MIN; idx < GDT_ENTRY_TLS_MAX; idx++) {
 97                 struct uml_tls_struct* curr =
 98                         &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];
 99 
100                 /*
101                  * Actually, now if it wasn't flushed it gets cleared and
102                  * flushed to the host, which will clear it.
103                  */
104                 if (!curr->present) {
105                         if (!curr->flushed) {
106                                 clear_user_desc(&curr->tls);
107                                 curr->tls.entry_number = idx;
108                         } else {
109                                 WARN_ON(!LDT_empty(&curr->tls));
110                                 continue;
111                         }
112                 }
113 
114                 if (!(flags & O_FORCE) && curr->flushed)
115                         continue;
116 
117                 ret = do_set_thread_area(&curr->tls);
118                 if (ret)
119                         goto out;
120 
121                 curr->flushed = 1;
122         }
123 out:
124         return ret;
125 }
126 
127 /*
128  * Verify if we need to do a flush for the new process, i.e. if there are any
129  * present desc's, only if they haven't been flushed.
130  */
131 static inline int needs_TLS_update(struct task_struct *task)
132 {
133         int i;
134         int ret = 0;
135 
136         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
137                 struct uml_tls_struct* curr =
138                         &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
139 
140                 /*
141                  * Can't test curr->present, we may need to clear a descriptor
142                  * which had a value.
143                  */
144                 if (curr->flushed)
145                         continue;
146                 ret = 1;
147                 break;
148         }
149         return ret;
150 }
151 
152 /*
153  * On a newly forked process, the TLS descriptors haven't yet been flushed. So
154  * we mark them as such and the first switch_to will do the job.
155  */
156 void clear_flushed_tls(struct task_struct *task)
157 {
158         int i;
159 
160         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
161                 struct uml_tls_struct* curr =
162                         &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
163 
164                 /*
165                  * Still correct to do this, if it wasn't present on the host it
166                  * will remain as flushed as it was.
167                  */
168                 if (!curr->present)
169                         continue;
170 
171                 curr->flushed = 0;
172         }
173 }
174 
175 /*
176  * In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
177  * common host process. So this is needed in SKAS0 too.
178  *
179  * However, if each thread had a different host process (and this was discussed
180  * for SMP support) this won't be needed.
181  *
182  * And this will not need be used when (and if) we'll add support to the host
183  * SKAS patch.
184  */
185 
186 int arch_switch_tls(struct task_struct *to)
187 {
188         if (!host_supports_tls)
189                 return 0;
190 
191         /*
192          * We have no need whatsoever to switch TLS for kernel threads; beyond
193          * that, that would also result in us calling os_set_thread_area with
194          * userspace_pid[cpu] == 0, which gives an error.
195          */
196         if (likely(to->mm))
197                 return load_TLS(O_FORCE, to);
198 
199         return 0;
200 }
201 
202 static int set_tls_entry(struct task_struct* task, struct user_desc *info,
203                          int idx, int flushed)
204 {
205         struct thread_struct *t = &task->thread;
206 
207         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
208                 return -EINVAL;
209 
210         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info;
211         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1;
212         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed;
213 
214         return 0;
215 }
216 
217 int arch_copy_tls(struct task_struct *new)
218 {
219         struct user_desc info;
220         int idx, ret = -EFAULT;
221 
222         if (copy_from_user(&info,
223                            (void __user *) UPT_SI(&new->thread.regs.regs),
224                            sizeof(info)))
225                 goto out;
226 
227         ret = -EINVAL;
228         if (LDT_empty(&info))
229                 goto out;
230 
231         idx = info.entry_number;
232 
233         ret = set_tls_entry(new, &info, idx, 0);
234 out:
235         return ret;
236 }
237 
238 /* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */
239 static int get_tls_entry(struct task_struct *task, struct user_desc *info,
240                          int idx)
241 {
242         struct thread_struct *t = &task->thread;
243 
244         if (!t->arch.tls_array)
245                 goto clear;
246 
247         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
248                 return -EINVAL;
249 
250         if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present)
251                 goto clear;
252 
253         *info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls;
254 
255 out:
256         /*
257          * Temporary debugging check, to make sure that things have been
258          * flushed. This could be triggered if load_TLS() failed.
259          */
260         if (unlikely(task == current &&
261                      !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) {
262                 printk(KERN_ERR "get_tls_entry: task with pid %d got here "
263                                 "without flushed TLS.", current->pid);
264         }
265 
266         return 0;
267 clear:
268         /*
269          * When the TLS entry has not been set, the values read to user in the
270          * tls_array are 0 (because it's cleared at boot, see
271          * arch/i386/kernel/head.S:cpu_gdt_table). Emulate that.
272          */
273         clear_user_desc(info);
274         info->entry_number = idx;
275         goto out;
276 }
277 
278 SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, user_desc)
279 {
280         struct user_desc info;
281         int idx, ret;
282 
283         if (!host_supports_tls)
284                 return -ENOSYS;
285 
286         if (copy_from_user(&info, user_desc, sizeof(info)))
287                 return -EFAULT;
288 
289         idx = info.entry_number;
290 
291         if (idx == -1) {
292                 idx = get_free_idx(current);
293                 if (idx < 0)
294                         return idx;
295                 info.entry_number = idx;
296                 /* Tell the user which slot we chose for him.*/
297                 if (put_user(idx, &user_desc->entry_number))
298                         return -EFAULT;
299         }
300 
301         ret = do_set_thread_area(&info);
302         if (ret)
303                 return ret;
304         return set_tls_entry(current, &info, idx, 1);
305 }
306 
307 /*
308  * Perform set_thread_area on behalf of the traced child.
309  * Note: error handling is not done on the deferred load, and this differ from
310  * i386. However the only possible error are caused by bugs.
311  */
312 int ptrace_set_thread_area(struct task_struct *child, int idx,
313                            struct user_desc __user *user_desc)
314 {
315         struct user_desc info;
316 
317         if (!host_supports_tls)
318                 return -EIO;
319 
320         if (copy_from_user(&info, user_desc, sizeof(info)))
321                 return -EFAULT;
322 
323         return set_tls_entry(child, &info, idx, 0);
324 }
325 
326 SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, user_desc)
327 {
328         struct user_desc info;
329         int idx, ret;
330 
331         if (!host_supports_tls)
332                 return -ENOSYS;
333 
334         if (get_user(idx, &user_desc->entry_number))
335                 return -EFAULT;
336 
337         ret = get_tls_entry(current, &info, idx);
338         if (ret < 0)
339                 goto out;
340 
341         if (copy_to_user(user_desc, &info, sizeof(info)))
342                 ret = -EFAULT;
343 
344 out:
345         return ret;
346 }
347 
348 /*
349  * Perform get_thread_area on behalf of the traced child.
350  */
351 int ptrace_get_thread_area(struct task_struct *child, int idx,
352                 struct user_desc __user *user_desc)
353 {
354         struct user_desc info;
355         int ret;
356 
357         if (!host_supports_tls)
358                 return -EIO;
359 
360         ret = get_tls_entry(child, &info, idx);
361         if (ret < 0)
362                 goto out;
363 
364         if (copy_to_user(user_desc, &info, sizeof(info)))
365                 ret = -EFAULT;
366 out:
367         return ret;
368 }
369 
370 /*
371  * This code is really i386-only, but it detects and logs x86_64 GDT indexes
372  * if a 32-bit UML is running on a 64-bit host.
373  */
374 static int __init __setup_host_supports_tls(void)
375 {
376         check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
377         if (host_supports_tls) {
378                 printk(KERN_INFO "Host TLS support detected\n");
379                 printk(KERN_INFO "Detected host type: ");
380                 switch (host_gdt_entry_tls_min) {
381                 case GDT_ENTRY_TLS_MIN_I386:
382                         printk(KERN_CONT "i386");
383                         break;
384                 case GDT_ENTRY_TLS_MIN_X86_64:
385                         printk(KERN_CONT "x86_64");
386                         break;
387                 }
388                 printk(KERN_CONT " (GDT indexes %d to %d)\n",
389                        host_gdt_entry_tls_min,
390                        host_gdt_entry_tls_min + GDT_ENTRY_TLS_ENTRIES);
391         } else
392                 printk(KERN_ERR "  Host TLS support NOT detected! "
393                                 "TLS support inside UML will not work\n");
394         return 0;
395 }
396 
397 __initcall(__setup_host_supports_tls);
398 

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