aboutsummaryrefslogtreecommitdiffstats
path: root/arch/um/sys-i386/tls.c
blob: c6c7131e563bcab77bf69cdfc1ef9160c8c6f9d4 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
/*
 * Copyright (C) 2005 Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
 * Licensed under the GPL
 */

#include "linux/percpu.h"
#include "linux/sched.h"
#include "asm/uaccess.h"
#include "os.h"
#include "skas.h"
#include "sysdep/tls.h"

/*
 * If needed we can detect when it's uninitialized.
 *
 * These are initialized in an initcall and unchanged thereafter.
 */
static int host_supports_tls = -1;
int host_gdt_entry_tls_min;

int do_set_thread_area(struct user_desc *info)
{
	int ret;
	u32 cpu;

	cpu = get_cpu();
	ret = os_set_thread_area(info, userspace_pid[cpu]);
	put_cpu();

	if (ret)
		printk(KERN_ERR "PTRACE_SET_THREAD_AREA failed, err = %d, "
		       "index = %d\n", ret, info->entry_number);

	return ret;
}

int do_get_thread_area(struct user_desc *info)
{
	int ret;
	u32 cpu;

	cpu = get_cpu();
	ret = os_get_thread_area(info, userspace_pid[cpu]);
	put_cpu();

	if (ret)
		printk(KERN_ERR "PTRACE_GET_THREAD_AREA failed, err = %d, "
		       "index = %d\n", ret, info->entry_number);

	return ret;
}

/*
 * sys_get_thread_area: get a yet unused TLS descriptor index.
 * XXX: Consider leaving one free slot for glibc usage at first place. This must
 * be done here (and by changing GDT_ENTRY_TLS_* macros) and nowhere else.
 *
 * Also, this must be tested when compiling in SKAS mode with dynamic linking
 * and running against NPTL.
 */
static int get_free_idx(struct task_struct* task)
{
	struct thread_struct *t = &task->thread;
	int idx;

	if (!t->arch.tls_array)
		return GDT_ENTRY_TLS_MIN;

	for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
		if (!t->arch.tls_array[idx].present)
			return idx + GDT_ENTRY_TLS_MIN;
	return -ESRCH;
}

static inline void clear_user_desc(struct user_desc* info)
{
	/* Postcondition: LDT_empty(info) returns true. */
	memset(info, 0, sizeof(*info));

	/*
	 * Check the LDT_empty or the i386 sys_get_thread_area code - we obtain
	 * indeed an empty user_desc.
	 */
	info->read_exec_only = 1;
	info->seg_not_present = 1;
}

#define O_FORCE 1

static int load_TLS(int flags, struct task_struct *to)
{
	int ret = 0;
	int idx;

	for (idx = GDT_ENTRY_TLS_MIN; idx < GDT_ENTRY_TLS_MAX; idx++) {
		struct uml_tls_struct* curr =
			&to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];

		/*
		 * Actually, now if it wasn't flushed it gets cleared and
		 * flushed to the host, which will clear it.
		 */
		if (!curr->present) {
			if (!curr->flushed) {
				clear_user_desc(&curr->tls);
				curr->tls.entry_number = idx;
			} else {
				WARN_ON(!LDT_empty(&curr->tls));
				continue;
			}
		}

		if (!(flags & O_FORCE) && curr->flushed)
			continue;

		ret = do_set_thread_area(&curr->tls);
		if (ret)
			goto out;

		curr->flushed = 1;
	}
out:
	return ret;
}

/*
 * Verify if we need to do a flush for the new process, i.e. if there are any
 * present desc's, only if they haven't been flushed.
 */
static inline int needs_TLS_update(struct task_struct *task)
{
	int i;
	int ret = 0;

	for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
		struct uml_tls_struct* curr =
			&task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];

		/*
		 * Can't test curr->present, we may need to clear a descriptor
		 * which had a value.
		 */
		if (curr->flushed)
			continue;
		ret = 1;
		break;
	}
	return ret;
}

/*
 * On a newly forked process, the TLS descriptors haven't yet been flushed. So
 * we mark them as such and the first switch_to will do the job.
 */
void clear_flushed_tls(struct task_struct *task)
{
	int i;

	for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
		struct uml_tls_struct* curr =
			&task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];

		/*
		 * Still correct to do this, if it wasn't present on the host it
		 * will remain as flushed as it was.
		 */
		if (!curr->present)
			continue;

		curr->flushed = 0;
	}
}

/*
 * In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
 * common host process. So this is needed in SKAS0 too.
 *
 * However, if each thread had a different host process (and this was discussed
 * for SMP support) this won't be needed.
 *
 * And this will not need be used when (and if) we'll add support to the host
 * SKAS patch.
 */

int arch_switch_tls(struct task_struct *to)
{
	if (!host_supports_tls)
		return 0;

	/*
	 * We have no need whatsoever to switch TLS for kernel threads; beyond
	 * that, that would also result in us calling os_set_thread_area with
	 * userspace_pid[cpu] == 0, which gives an error.
	 */
	if (likely(to->mm))
		return load_TLS(O_FORCE, to);

	return 0;
}

static int set_tls_entry(struct task_struct* task, struct user_desc *info,
			 int idx, int flushed)
{
	struct thread_struct *t = &task->thread;

	if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
		return -EINVAL;

	t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info;
	t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1;
	t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed;

	return 0;
}

int arch_copy_tls(struct task_struct *new)
{
	struct user_desc info;
	int idx, ret = -EFAULT;

	if (copy_from_user(&info,
			   (void __user *) UPT_ESI(&new->thread.regs.regs),
			   sizeof(info)))
		goto out;

	ret = -EINVAL;
	if (LDT_empty(&info))
		goto out;

	idx = info.entry_number;

	ret = set_tls_entry(new, &info, idx, 0);
out:
	return ret;
}

/* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */
static int get_tls_entry(struct task_struct *task, struct user_desc *info,
			 int idx)
{
	struct thread_struct *t = &task->thread;

	if (!t->arch.tls_array)
		goto clear;

	if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
		return -EINVAL;

	if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present)
		goto clear;

	*info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls;

out:
	/*
	 * Temporary debugging check, to make sure that things have been
	 * flushed. This could be triggered if load_TLS() failed.
	 */
	if (unlikely(task == current &&
		     !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) {
		printk(KERN_ERR "get_tls_entry: task with pid %d got here "
				"without flushed TLS.", current->pid);
	}

	return 0;
clear:
	/*
	 * When the TLS entry has not been set, the values read to user in the
	 * tls_array are 0 (because it's cleared at boot, see
	 * arch/i386/kernel/head.S:cpu_gdt_table). Emulate that.
	 */
	clear_user_desc(info);
	info->entry_number = idx;
	goto out;
}

int sys_set_thread_area(struct user_desc __user *user_desc)
{
	struct user_desc info;
	int idx, ret;

	if (!host_supports_tls)
		return -ENOSYS;

	if (copy_from_user(&info, user_desc, sizeof(info)))
		return -EFAULT;

	idx = info.entry_number;

	if (idx == -1) {
		idx = get_free_idx(current);
		if (idx < 0)
			return idx;
		info.entry_number = idx;
		/* Tell the user which slot we chose for him.*/
		if (put_user(idx, &user_desc->entry_number))
			return -EFAULT;
	}

	ret = do_set_thread_area(&info);
	if (ret)
		return ret;
	return set_tls_entry(current, &info, idx, 1);
}

/*
 * Perform set_thread_area on behalf of the traced child.
 * Note: error handling is not done on the deferred load, and this differ from
 * i386. However the only possible error are caused by bugs.
 */
int ptrace_set_thread_area(struct task_struct *child, int idx,
			   struct user_desc __user *user_desc)
{
	struct user_desc info;

	if (!host_supports_tls)
		return -EIO;

	if (copy_from_user(&info, user_desc, sizeof(info)))
		return -EFAULT;

	return set_tls_entry(child, &info, idx, 0);
}

int sys_get_thread_area(struct user_desc __user *user_desc)
{
	struct user_desc info;
	int idx, ret;

	if (!host_supports_tls)
		return -ENOSYS;

	if (get_user(idx, &user_desc->entry_number))
		return -EFAULT;

	ret = get_tls_entry(current, &info, idx);
	if (ret < 0)
		goto out;

	if (copy_to_user(user_desc, &info, sizeof(info)))
		ret = -EFAULT;

out:
	return ret;
}

/*
 * Perform get_thread_area on behalf of the traced child.
 */
int ptrace_get_thread_area(struct task_struct *child, int idx,
		struct user_desc __user *user_desc)
{
	struct user_desc info;
	int ret;

	if (!host_supports_tls)
		return -EIO;

	ret = get_tls_entry(child, &info, idx);
	if (ret < 0)
		goto out;

	if (copy_to_user(user_desc, &info, sizeof(info)))
		ret = -EFAULT;
out:
	return ret;
}

/*
 * This code is really i386-only, but it detects and logs x86_64 GDT indexes
 * if a 32-bit UML is running on a 64-bit host.
 */
static int __init __setup_host_supports_tls(void)
{
	check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
	if (host_supports_tls) {
		printk(KERN_INFO "Host TLS support detected\n");
		printk(KERN_INFO "Detected host type: ");
		switch (host_gdt_entry_tls_min) {
		case GDT_ENTRY_TLS_MIN_I386:
			printk(KERN_CONT "i386");
			break;
		case GDT_ENTRY_TLS_MIN_X86_64:
			printk(KERN_CONT "x86_64");
			break;
		}
		printk(KERN_CONT " (GDT indexes %d to %d)\n",
		       host_gdt_entry_tls_min,
		       host_gdt_entry_tls_min + GDT_ENTRY_TLS_ENTRIES);
	} else
		printk(KERN_ERR "  Host TLS support NOT detected! "
				"TLS support inside UML will not work\n");
	return 0;
}

__initcall(__setup_host_supports_tls);