Merge Btrfs into fs/btrfs
[linux-2.6] / arch / um / sys-i386 / tls.c
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 "asm/uaccess.h"
9 #include "os.h"
10 #include "skas.h"
11 #include "sysdep/tls.h"
12
13 /*
14  * If needed we can detect when it's uninitialized.
15  *
16  * These are initialized in an initcall and unchanged thereafter.
17  */
18 static int host_supports_tls = -1;
19 int host_gdt_entry_tls_min;
20
21 int do_set_thread_area(struct user_desc *info)
22 {
23         int ret;
24         u32 cpu;
25
26         cpu = get_cpu();
27         ret = os_set_thread_area(info, userspace_pid[cpu]);
28         put_cpu();
29
30         if (ret)
31                 printk(KERN_ERR "PTRACE_SET_THREAD_AREA failed, err = %d, "
32                        "index = %d\n", ret, info->entry_number);
33
34         return ret;
35 }
36
37 int do_get_thread_area(struct user_desc *info)
38 {
39         int ret;
40         u32 cpu;
41
42         cpu = get_cpu();
43         ret = os_get_thread_area(info, userspace_pid[cpu]);
44         put_cpu();
45
46         if (ret)
47                 printk(KERN_ERR "PTRACE_GET_THREAD_AREA failed, err = %d, "
48                        "index = %d\n", ret, info->entry_number);
49
50         return ret;
51 }
52
53 /*
54  * sys_get_thread_area: get a yet unused TLS descriptor index.
55  * XXX: Consider leaving one free slot for glibc usage at first place. This must
56  * be done here (and by changing GDT_ENTRY_TLS_* macros) and nowhere else.
57  *
58  * Also, this must be tested when compiling in SKAS mode with dynamic linking
59  * and running against NPTL.
60  */
61 static int get_free_idx(struct task_struct* task)
62 {
63         struct thread_struct *t = &task->thread;
64         int idx;
65
66         if (!t->arch.tls_array)
67                 return GDT_ENTRY_TLS_MIN;
68
69         for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
70                 if (!t->arch.tls_array[idx].present)
71                         return idx + GDT_ENTRY_TLS_MIN;
72         return -ESRCH;
73 }
74
75 static inline void clear_user_desc(struct user_desc* info)
76 {
77         /* Postcondition: LDT_empty(info) returns true. */
78         memset(info, 0, sizeof(*info));
79
80         /*
81          * Check the LDT_empty or the i386 sys_get_thread_area code - we obtain
82          * indeed an empty user_desc.
83          */
84         info->read_exec_only = 1;
85         info->seg_not_present = 1;
86 }
87
88 #define O_FORCE 1
89
90 static int load_TLS(int flags, struct task_struct *to)
91 {
92         int ret = 0;
93         int idx;
94
95         for (idx = GDT_ENTRY_TLS_MIN; idx < GDT_ENTRY_TLS_MAX; idx++) {
96                 struct uml_tls_struct* curr =
97                         &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];
98
99                 /*
100                  * Actually, now if it wasn't flushed it gets cleared and
101                  * flushed to the host, which will clear it.
102                  */
103                 if (!curr->present) {
104                         if (!curr->flushed) {
105                                 clear_user_desc(&curr->tls);
106                                 curr->tls.entry_number = idx;
107                         } else {
108                                 WARN_ON(!LDT_empty(&curr->tls));
109                                 continue;
110                         }
111                 }
112
113                 if (!(flags & O_FORCE) && curr->flushed)
114                         continue;
115
116                 ret = do_set_thread_area(&curr->tls);
117                 if (ret)
118                         goto out;
119
120                 curr->flushed = 1;
121         }
122 out:
123         return ret;
124 }
125
126 /*
127  * Verify if we need to do a flush for the new process, i.e. if there are any
128  * present desc's, only if they haven't been flushed.
129  */
130 static inline int needs_TLS_update(struct task_struct *task)
131 {
132         int i;
133         int ret = 0;
134
135         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
136                 struct uml_tls_struct* curr =
137                         &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
138
139                 /*
140                  * Can't test curr->present, we may need to clear a descriptor
141                  * which had a value.
142                  */
143                 if (curr->flushed)
144                         continue;
145                 ret = 1;
146                 break;
147         }
148         return ret;
149 }
150
151 /*
152  * On a newly forked process, the TLS descriptors haven't yet been flushed. So
153  * we mark them as such and the first switch_to will do the job.
154  */
155 void clear_flushed_tls(struct task_struct *task)
156 {
157         int i;
158
159         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
160                 struct uml_tls_struct* curr =
161                         &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
162
163                 /*
164                  * Still correct to do this, if it wasn't present on the host it
165                  * will remain as flushed as it was.
166                  */
167                 if (!curr->present)
168                         continue;
169
170                 curr->flushed = 0;
171         }
172 }
173
174 /*
175  * In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
176  * common host process. So this is needed in SKAS0 too.
177  *
178  * However, if each thread had a different host process (and this was discussed
179  * for SMP support) this won't be needed.
180  *
181  * And this will not need be used when (and if) we'll add support to the host
182  * SKAS patch.
183  */
184
185 int arch_switch_tls(struct task_struct *to)
186 {
187         if (!host_supports_tls)
188                 return 0;
189
190         /*
191          * We have no need whatsoever to switch TLS for kernel threads; beyond
192          * that, that would also result in us calling os_set_thread_area with
193          * userspace_pid[cpu] == 0, which gives an error.
194          */
195         if (likely(to->mm))
196                 return load_TLS(O_FORCE, to);
197
198         return 0;
199 }
200
201 static int set_tls_entry(struct task_struct* task, struct user_desc *info,
202                          int idx, int flushed)
203 {
204         struct thread_struct *t = &task->thread;
205
206         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
207                 return -EINVAL;
208
209         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info;
210         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1;
211         t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed;
212
213         return 0;
214 }
215
216 int arch_copy_tls(struct task_struct *new)
217 {
218         struct user_desc info;
219         int idx, ret = -EFAULT;
220
221         if (copy_from_user(&info,
222                            (void __user *) UPT_ESI(&new->thread.regs.regs),
223                            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 int sys_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 int sys_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);