643dab58572739d2b1f36f5c4ef32e6e0c1ebcc2
[linux-2.6.git] / 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/kernel.h"
7 #include "linux/sched.h"
8 #include "linux/slab.h"
9 #include "linux/types.h"
10 #include "asm/uaccess.h"
11 #include "asm/ptrace.h"
12 #include "asm/segment.h"
13 #include "asm/smp.h"
14 #include "asm/desc.h"
15 #include "choose-mode.h"
16 #include "kern.h"
17 #include "kern_util.h"
18 #include "mode_kern.h"
19 #include "os.h"
20 #include "mode.h"
21
22 #ifdef CONFIG_MODE_SKAS
23 #include "skas.h"
24 #endif
25
26 /* If needed we can detect when it's uninitialized. */
27 static int host_supports_tls = -1;
28 int host_gdt_entry_tls_min = -1;
29
30 #ifdef CONFIG_MODE_SKAS
31 int do_set_thread_area_skas(struct user_desc *info)
32 {
33         int ret;
34         u32 cpu;
35
36         cpu = get_cpu();
37         ret = os_set_thread_area(info, userspace_pid[cpu]);
38         put_cpu();
39         return ret;
40 }
41
42 int do_get_thread_area_skas(struct user_desc *info)
43 {
44         int ret;
45         u32 cpu;
46
47         cpu = get_cpu();
48         ret = os_get_thread_area(info, userspace_pid[cpu]);
49         put_cpu();
50         return ret;
51 }
52 #endif
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 dinamic 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         /* 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 = &to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];
97
98                 /* Actually, now if it wasn't flushed it gets cleared and
99                  * flushed to the host, which will clear it.*/
100                 if (!curr->present) {
101                         if (!curr->flushed) {
102                                 clear_user_desc(&curr->tls);
103                                 curr->tls.entry_number = idx;
104                         } else {
105                                 WARN_ON(!LDT_empty(&curr->tls));
106                                 continue;
107                         }
108                 }
109
110                 if (!(flags & O_FORCE) && curr->flushed)
111                         continue;
112
113                 ret = do_set_thread_area(&curr->tls);
114                 if (ret)
115                         goto out;
116
117                 curr->flushed = 1;
118         }
119 out:
120         return ret;
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 = &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
133
134                 /* Can't test curr->present, we may need to clear a descriptor
135                  * which had a value. */
136                 if (curr->flushed)
137                         continue;
138                 ret = 1;
139                 break;
140         }
141         return ret;
142 }
143
144 /* On a newly forked process, the TLS descriptors haven't yet been flushed. So
145  * we mark them as such and the first switch_to will do the job.
146  */
147 void clear_flushed_tls(struct task_struct *task)
148 {
149         int i;
150
151         for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
152                 struct uml_tls_struct* curr = &task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
153
154                 /* Still correct to do this, if it wasn't present on the host it
155                  * will remain as flushed as it was. */
156                 if (!curr->present)
157                         continue;
158
159                 curr->flushed = 0;
160         }
161 }
162
163 /* In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
164  * common host process. So this is needed in SKAS0 too.
165  *
166  * However, if each thread had a different host process (and this was discussed
167  * for SMP support) this won't be needed.
168  *
169  * And this will not need be used when (and if) we'll add support to the host
170  * SKAS patch. */
171
172 int arch_switch_tls_skas(struct task_struct *from, struct task_struct *to)
173 {
174         if (!host_supports_tls)
175                 return 0;
176
177         /* We have no need whatsoever to switch TLS for kernel threads; beyond
178          * that, that would also result in us calling os_set_thread_area with
179          * userspace_pid[cpu] == 0, which gives an error. */
180         if (likely(to->mm))
181                 return load_TLS(O_FORCE, to);
182
183         return 0;
184 }
185
186 int arch_switch_tls_tt(struct task_struct *from, struct task_struct *to)
187 {
188         if (!host_supports_tls)
189                 return 0;
190
191         if (needs_TLS_update(to))
192                 return load_TLS(0, 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_copy_tls(struct task_struct *new)
213 {
214         struct user_desc info;
215         int idx, ret = -EFAULT;
216
217         if (copy_from_user(&info,
218                            (void __user *) UPT_ESI(&new->thread.regs.regs),
219                            sizeof(info)))
220                 goto out;
221
222         ret = -EINVAL;
223         if (LDT_empty(&info))
224                 goto out;
225
226         idx = info.entry_number;
227
228         ret = set_tls_entry(new, &info, idx, 0);
229 out:
230         return ret;
231 }
232
233 /* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */
234 static int get_tls_entry(struct task_struct* task, struct user_desc *info, int idx)
235 {
236         struct thread_struct *t = &task->thread;
237
238         if (!t->arch.tls_array)
239                 goto clear;
240
241         if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
242                 return -EINVAL;
243
244         if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present)
245                 goto clear;
246
247         *info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls;
248
249 out:
250         /* Temporary debugging check, to make sure that things have been
251          * flushed. This could be triggered if load_TLS() failed.
252          */
253         if (unlikely(task == current && !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) {
254                 printk(KERN_ERR "get_tls_entry: task with pid %d got here "
255                                 "without flushed TLS.", current->pid);
256         }
257
258         return 0;
259 clear:
260         /* When the TLS entry has not been set, the values read to user in the
261          * tls_array are 0 (because it's cleared at boot, see
262          * arch/i386/kernel/head.S:cpu_gdt_table). Emulate that.
263          */
264         clear_user_desc(info);
265         info->entry_number = idx;
266         goto out;
267 }
268
269 asmlinkage int sys_set_thread_area(struct user_desc __user *user_desc)
270 {
271         struct user_desc info;
272         int idx, ret;
273
274         if (!host_supports_tls)
275                 return -ENOSYS;
276
277         if (copy_from_user(&info, user_desc, sizeof(info)))
278                 return -EFAULT;
279
280         idx = info.entry_number;
281
282         if (idx == -1) {
283                 idx = get_free_idx(current);
284                 if (idx < 0)
285                         return idx;
286                 info.entry_number = idx;
287                 /* Tell the user which slot we chose for him.*/
288                 if (put_user(idx, &user_desc->entry_number))
289                         return -EFAULT;
290         }
291
292         ret = CHOOSE_MODE_PROC(do_set_thread_area_tt, do_set_thread_area_skas, &info);
293         if (ret)
294                 return ret;
295         return set_tls_entry(current, &info, idx, 1);
296 }
297
298 /*
299  * Perform set_thread_area on behalf of the traced child.
300  * Note: error handling is not done on the deferred load, and this differ from
301  * i386. However the only possible error are caused by bugs.
302  */
303 int ptrace_set_thread_area(struct task_struct *child, int idx,
304                 struct user_desc __user *user_desc)
305 {
306         struct user_desc info;
307
308         if (!host_supports_tls)
309                 return -EIO;
310
311         if (copy_from_user(&info, user_desc, sizeof(info)))
312                 return -EFAULT;
313
314         return set_tls_entry(child, &info, idx, 0);
315 }
316
317 asmlinkage int sys_get_thread_area(struct user_desc __user *user_desc)
318 {
319         struct user_desc info;
320         int idx, ret;
321
322         if (!host_supports_tls)
323                 return -ENOSYS;
324
325         if (get_user(idx, &user_desc->entry_number))
326                 return -EFAULT;
327
328         ret = get_tls_entry(current, &info, idx);
329         if (ret < 0)
330                 goto out;
331
332         if (copy_to_user(user_desc, &info, sizeof(info)))
333                 ret = -EFAULT;
334
335 out:
336         return ret;
337 }
338
339 /*
340  * Perform get_thread_area on behalf of the traced child.
341  */
342 int ptrace_get_thread_area(struct task_struct *child, int idx,
343                 struct user_desc __user *user_desc)
344 {
345         struct user_desc info;
346         int ret;
347
348         if (!host_supports_tls)
349                 return -EIO;
350
351         ret = get_tls_entry(child, &info, idx);
352         if (ret < 0)
353                 goto out;
354
355         if (copy_to_user(user_desc, &info, sizeof(info)))
356                 ret = -EFAULT;
357 out:
358         return ret;
359 }
360
361
362 /* XXX: This part is probably common to i386 and x86-64. Don't create a common
363  * file for now, do that when implementing x86-64 support.*/
364 static int __init __setup_host_supports_tls(void) {
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("i386\n");
372                                 break;
373                         case GDT_ENTRY_TLS_MIN_X86_64:
374                                 printk("x86_64\n");
375                                 break;
376                 }
377         } else
378                 printk(KERN_ERR "  Host TLS support NOT detected! "
379                                 "TLS support inside UML will not work\n");
380         return 0;
381 }
382
383 __initcall(__setup_host_supports_tls);