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

source code of linux/arch/x86/um/tls_32.c