tls_32.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 <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(&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, &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, 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(&info, (void __user *) tls, 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(new, &info, idx, 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(&info, user_desc, 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, idx, 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(&info, user_desc, sizeof(info)))
310		return -EFAULT;
311
312	return set_tls_entry(child, &info, idx, 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, idx);
327	if (ret < 0)
328		goto out;
329
330	if (copy_to_user(user_desc, &info, 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(child, &info, idx);
350	if (ret < 0)
351		goto out;
352
353	if (copy_to_user(user_desc, &info, 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);