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 <asm/uaccess.h>
10#include <asm/ptrace-abi.h>
11#include <os.h>
12#include <skas.h>
13#include <sysdep/tls.h>
14
15/*
16 * If needed we can detect when it's uninitialized.
17 *
18 * These are initialized in an initcall and unchanged thereafter.
19 */
20static int host_supports_tls = -1;
21int host_gdt_entry_tls_min;
22
23int do_set_thread_area(struct user_desc *info)
24{
25	int ret;
26	u32 cpu;
27
28	cpu = get_cpu();
29	ret = os_set_thread_area(info, userspace_pid[cpu]);
30	put_cpu();
31
32	if (ret)
33		printk(KERN_ERR "PTRACE_SET_THREAD_AREA failed, err = %d, "
34		       "index = %d\n", ret, info->entry_number);
35
36	return ret;
37}
38
39int do_get_thread_area(struct user_desc *info)
40{
41	int ret;
42	u32 cpu;
43
44	cpu = get_cpu();
45	ret = os_get_thread_area(info, userspace_pid[cpu]);
46	put_cpu();
47
48	if (ret)
49		printk(KERN_ERR "PTRACE_GET_THREAD_AREA failed, err = %d, "
50		       "index = %d\n", ret, info->entry_number);
51
52	return ret;
53}
54
55/*
56 * sys_get_thread_area: get a yet unused TLS descriptor index.
57 * XXX: Consider leaving one free slot for glibc usage at first place. This must
58 * be done here (and by changing GDT_ENTRY_TLS_* macros) and nowhere else.
59 *
60 * Also, this must be tested when compiling in SKAS mode with dynamic linking
61 * and running against NPTL.
62 */
63static int get_free_idx(struct task_struct* task)
64{
65	struct thread_struct *t = &task->thread;
66	int idx;
67
68	if (!t->arch.tls_array)
69		return GDT_ENTRY_TLS_MIN;
70
71	for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
72		if (!t->arch.tls_array[idx].present)
73			return idx + GDT_ENTRY_TLS_MIN;
74	return -ESRCH;
75}
76
77static inline void clear_user_desc(struct user_desc* info)
78{
79	/* Postcondition: LDT_empty(info) returns true. */
80	memset(info, 0, sizeof(*info));
81
82	/*
83	 * Check the LDT_empty or the i386 sys_get_thread_area code - we obtain
84	 * indeed an empty user_desc.
85	 */
86	info->read_exec_only = 1;
87	info->seg_not_present = 1;
88}
89
90#define O_FORCE 1
91
92static int load_TLS(int flags, struct task_struct *to)
93{
94	int ret = 0;
95	int idx;
96
97	for (idx = GDT_ENTRY_TLS_MIN; idx < GDT_ENTRY_TLS_MAX; idx++) {
98		struct uml_tls_struct* curr =
99			&to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];
100
101		/*
102		 * Actually, now if it wasn't flushed it gets cleared and
103		 * flushed to the host, which will clear it.
104		 */
105		if (!curr->present) {
106			if (!curr->flushed) {
107				clear_user_desc(&curr->tls);
108				curr->tls.entry_number = idx;
109			} else {
110				WARN_ON(!LDT_empty(&curr->tls));
111				continue;
112			}
113		}
114
115		if (!(flags & O_FORCE) && curr->flushed)
116			continue;
117
118		ret = do_set_thread_area(&curr->tls);
119		if (ret)
120			goto out;
121
122		curr->flushed = 1;
123	}
124out:
125	return ret;
126}
127
128/*
129 * Verify if we need to do a flush for the new process, i.e. if there are any
130 * present desc's, only if they haven't been flushed.
131 */
132static inline int needs_TLS_update(struct task_struct *task)
133{
134	int i;
135	int ret = 0;
136
137	for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
138		struct uml_tls_struct* curr =
139			&task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
140
141		/*
142		 * Can't test curr->present, we may need to clear a descriptor
143		 * which had a value.
144		 */
145		if (curr->flushed)
146			continue;
147		ret = 1;
148		break;
149	}
150	return ret;
151}
152
153/*
154 * On a newly forked process, the TLS descriptors haven't yet been flushed. So
155 * we mark them as such and the first switch_to will do the job.
156 */
157void clear_flushed_tls(struct task_struct *task)
158{
159	int i;
160
161	for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
162		struct uml_tls_struct* curr =
163			&task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
164
165		/*
166		 * Still correct to do this, if it wasn't present on the host it
167		 * will remain as flushed as it was.
168		 */
169		if (!curr->present)
170			continue;
171
172		curr->flushed = 0;
173	}
174}
175
176/*
177 * In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
178 * common host process. So this is needed in SKAS0 too.
179 *
180 * However, if each thread had a different host process (and this was discussed
181 * for SMP support) this won't be needed.
182 *
183 * And this will not need be used when (and if) we'll add support to the host
184 * SKAS patch.
185 */
186
187int arch_switch_tls(struct task_struct *to)
188{
189	if (!host_supports_tls)
190		return 0;
191
192	/*
193	 * We have no need whatsoever to switch TLS for kernel threads; beyond
194	 * that, that would also result in us calling os_set_thread_area with
195	 * userspace_pid[cpu] == 0, which gives an error.
196	 */
197	if (likely(to->mm))
198		return load_TLS(O_FORCE, to);
199
200	return 0;
201}
202
203static int set_tls_entry(struct task_struct* task, struct user_desc *info,
204			 int idx, int flushed)
205{
206	struct thread_struct *t = &task->thread;
207
208	if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
209		return -EINVAL;
210
211	t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info;
212	t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1;
213	t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed;
214
215	return 0;
216}
217
218int arch_copy_tls(struct task_struct *new)
219{
220	struct user_desc info;
221	int idx, ret = -EFAULT;
222
223	if (copy_from_user(&info,
224			   (void __user *) UPT_SI(&new->thread.regs.regs),
225			   sizeof(info)))
226		goto out;
227
228	ret = -EINVAL;
229	if (LDT_empty(&info))
230		goto out;
231
232	idx = info.entry_number;
233
234	ret = set_tls_entry(new, &info, idx, 0);
235out:
236	return ret;
237}
238
239/* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */
240static int get_tls_entry(struct task_struct *task, struct user_desc *info,
241			 int idx)
242{
243	struct thread_struct *t = &task->thread;
244
245	if (!t->arch.tls_array)
246		goto clear;
247
248	if (idx < GDT_ENTRY_TLS_MIN || idx > GDT_ENTRY_TLS_MAX)
249		return -EINVAL;
250
251	if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present)
252		goto clear;
253
254	*info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls;
255
256out:
257	/*
258	 * Temporary debugging check, to make sure that things have been
259	 * flushed. This could be triggered if load_TLS() failed.
260	 */
261	if (unlikely(task == current &&
262		     !t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) {
263		printk(KERN_ERR "get_tls_entry: task with pid %d got here "
264				"without flushed TLS.", current->pid);
265	}
266
267	return 0;
268clear:
269	/*
270	 * When the TLS entry has not been set, the values read to user in the
271	 * tls_array are 0 (because it's cleared at boot, see
272	 * arch/i386/kernel/head.S:cpu_gdt_table). Emulate that.
273	 */
274	clear_user_desc(info);
275	info->entry_number = idx;
276	goto out;
277}
278
279SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, user_desc)
280{
281	struct user_desc info;
282	int idx, ret;
283
284	if (!host_supports_tls)
285		return -ENOSYS;
286
287	if (copy_from_user(&info, user_desc, sizeof(info)))
288		return -EFAULT;
289
290	idx = info.entry_number;
291
292	if (idx == -1) {
293		idx = get_free_idx(current);
294		if (idx < 0)
295			return idx;
296		info.entry_number = idx;
297		/* Tell the user which slot we chose for him.*/
298		if (put_user(idx, &user_desc->entry_number))
299			return -EFAULT;
300	}
301
302	ret = do_set_thread_area(&info);
303	if (ret)
304		return ret;
305	return set_tls_entry(current, &info, idx, 1);
306}
307
308/*
309 * Perform set_thread_area on behalf of the traced child.
310 * Note: error handling is not done on the deferred load, and this differ from
311 * i386. However the only possible error are caused by bugs.
312 */
313int ptrace_set_thread_area(struct task_struct *child, int idx,
314			   struct user_desc __user *user_desc)
315{
316	struct user_desc info;
317
318	if (!host_supports_tls)
319		return -EIO;
320
321	if (copy_from_user(&info, user_desc, sizeof(info)))
322		return -EFAULT;
323
324	return set_tls_entry(child, &info, idx, 0);
325}
326
327SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, user_desc)
328{
329	struct user_desc info;
330	int idx, ret;
331
332	if (!host_supports_tls)
333		return -ENOSYS;
334
335	if (get_user(idx, &user_desc->entry_number))
336		return -EFAULT;
337
338	ret = get_tls_entry(current, &info, idx);
339	if (ret < 0)
340		goto out;
341
342	if (copy_to_user(user_desc, &info, sizeof(info)))
343		ret = -EFAULT;
344
345out:
346	return ret;
347}
348
349/*
350 * Perform get_thread_area on behalf of the traced child.
351 */
352int ptrace_get_thread_area(struct task_struct *child, int idx,
353		struct user_desc __user *user_desc)
354{
355	struct user_desc info;
356	int ret;
357
358	if (!host_supports_tls)
359		return -EIO;
360
361	ret = get_tls_entry(child, &info, idx);
362	if (ret < 0)
363		goto out;
364
365	if (copy_to_user(user_desc, &info, sizeof(info)))
366		ret = -EFAULT;
367out:
368	return ret;
369}
370
371/*
372 * This code is really i386-only, but it detects and logs x86_64 GDT indexes
373 * if a 32-bit UML is running on a 64-bit host.
374 */
375static int __init __setup_host_supports_tls(void)
376{
377	check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
378	if (host_supports_tls) {
379		printk(KERN_INFO "Host TLS support detected\n");
380		printk(KERN_INFO "Detected host type: ");
381		switch (host_gdt_entry_tls_min) {
382		case GDT_ENTRY_TLS_MIN_I386:
383			printk(KERN_CONT "i386");
384			break;
385		case GDT_ENTRY_TLS_MIN_X86_64:
386			printk(KERN_CONT "x86_64");
387			break;
388		}
389		printk(KERN_CONT " (GDT indexes %d to %d)\n",
390		       host_gdt_entry_tls_min,
391		       host_gdt_entry_tls_min + GDT_ENTRY_TLS_ENTRIES);
392	} else
393		printk(KERN_ERR "  Host TLS support NOT detected! "
394				"TLS support inside UML will not work\n");
395	return 0;
396}
397
398__initcall(__setup_host_supports_tls);
399