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