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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 "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 */
18static int host_supports_tls = -1;
19int host_gdt_entry_tls_min;
20
21int 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
37int 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 */
61static 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
75static 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
90static 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 }
122out:
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 */
130static 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 */
155void 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
185int 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
201static 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
216int 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_SI(&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);
233out:
234 return ret;
235}
236
237/* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */
238static 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
254out:
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;
266clear:
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
277int 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 */
311int 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
325int 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
343out:
344 return ret;
345}
346
347/*
348 * Perform get_thread_area on behalf of the traced child.
349 */
350int 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;
365out:
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 */
373static 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);