/arch/um/sys-i386/tls.c

  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_ESI(&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);