[mirror_ubuntu-bionic-kernel.git] / arch / x86 / um / tls_32.c

/*
 * Copyright (C) 2005 Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
 * Licensed under the GPL
 */

#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/syscalls.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_SI(&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;
}

SYSCALL_DEFINE1(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);
}

SYSCALL_DEFINE1(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);
Commit	Line	Data
aa6758d4 PBG	1	/*
	2	* Copyright (C) 2005 Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
	3	* Licensed under the GPL
	4	*/
	5
37185b33 AV	6	#include <linux/percpu.h>
37185b33 AV	7	#include <linux/sched.h>
2cf09666	8	#include <linux/syscalls.h>
37185b33 AV	9	#include <asm/uaccess.h>
	10	#include <os.h>
	11	#include <skas.h>
	12	#include <sysdep/tls.h>
aa6758d4	13
65a58ab0 JD	14	/*
	15	* If needed we can detect when it's uninitialized.
	16	*
	17	* These are initialized in an initcall and unchanged thereafter.
	18	*/
3feb8856	19	static int host_supports_tls = -1;
65a58ab0	20	int host_gdt_entry_tls_min;
3feb8856	21
6aa802ce	22	int do_set_thread_area(struct user_desc *info)
aa6758d4 PBG	23	{
	24	int ret;
	25	u32 cpu;
	26
	27	cpu = get_cpu();
	28	ret = os_set_thread_area(info, userspace_pid[cpu]);
	29	put_cpu();
b8bec829 JD	30
	31	if (ret)
	32	printk(KERN_ERR "PTRACE_SET_THREAD_AREA failed, err = %d, "
	33	"index = %d\n", ret, info->entry_number);
	34
aa6758d4 PBG	35	return ret;
	36	}
	37
6aa802ce	38	int do_get_thread_area(struct user_desc *info)
aa6758d4 PBG	39	{
	40	int ret;
	41	u32 cpu;
	42
	43	cpu = get_cpu();
	44	ret = os_get_thread_area(info, userspace_pid[cpu]);
	45	put_cpu();
b8bec829 JD	46
	47	if (ret)
	48	printk(KERN_ERR "PTRACE_GET_THREAD_AREA failed, err = %d, "
	49	"index = %d\n", ret, info->entry_number);
	50
aa6758d4 PBG	51	return ret;
aa6758d4 PBG	52	}
aa6758d4 PBG	53
	54	/*
	55	* sys_get_thread_area: get a yet unused TLS descriptor index.
	56	* XXX: Consider leaving one free slot for glibc usage at first place. This must
	57	* be done here (and by changing GDT_ENTRY_TLS_* macros) and nowhere else.
	58	*
b60745b9	59	* Also, this must be tested when compiling in SKAS mode with dynamic linking
aa6758d4 PBG	60	* and running against NPTL.
	61	*/
	62	static int get_free_idx(struct task_struct* task)
	63	{
	64	struct thread_struct *t = &task->thread;
	65	int idx;
	66
	67	if (!t->arch.tls_array)
	68	return GDT_ENTRY_TLS_MIN;
	69
	70	for (idx = 0; idx < GDT_ENTRY_TLS_ENTRIES; idx++)
	71	if (!t->arch.tls_array[idx].present)
	72	return idx + GDT_ENTRY_TLS_MIN;
	73	return -ESRCH;
	74	}
	75
aa6758d4 PBG	76	static inline void clear_user_desc(struct user_desc* info)
	77	{
	78	/* Postcondition: LDT_empty(info) returns true. */
	79	memset(info, 0, sizeof(*info));
	80
ba180fd4 JD	81	/*
ba180fd4 JD	82	* Check the LDT_empty or the i386 sys_get_thread_area code - we obtain
aa6758d4 PBG	83	* indeed an empty user_desc.
	84	*/
	85	info->read_exec_only = 1;
	86	info->seg_not_present = 1;
	87	}
	88
54d8d3b5 PBG	89	#define O_FORCE 1
54d8d3b5 PBG	90
aa6758d4 PBG	91	static int load_TLS(int flags, struct task_struct *to)
	92	{
	93	int ret = 0;
	94	int idx;
	95
	96	for (idx = GDT_ENTRY_TLS_MIN; idx < GDT_ENTRY_TLS_MAX; idx++) {
ba180fd4 JD	97	struct uml_tls_struct* curr =
ba180fd4 JD	98	&to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];
aa6758d4	99
ba180fd4 JD	100	/*
	101	* Actually, now if it wasn't flushed it gets cleared and
	102	* flushed to the host, which will clear it.
	103	*/
aa6758d4 PBG	104	if (!curr->present) {
	105	if (!curr->flushed) {
	106	clear_user_desc(&curr->tls);
	107	curr->tls.entry_number = idx;
	108	} else {
	109	WARN_ON(!LDT_empty(&curr->tls));
	110	continue;
	111	}
	112	}
	113
	114	if (!(flags & O_FORCE) && curr->flushed)
	115	continue;
	116
	117	ret = do_set_thread_area(&curr->tls);
	118	if (ret)
	119	goto out;
	120
	121	curr->flushed = 1;
	122	}
	123	out:
	124	return ret;
	125	}
	126
ba180fd4 JD	127	/*
ba180fd4 JD	128	* Verify if we need to do a flush for the new process, i.e. if there are any
aa6758d4 PBG	129	* present desc's, only if they haven't been flushed.
	130	*/
	131	static inline int needs_TLS_update(struct task_struct *task)
	132	{
	133	int i;
	134	int ret = 0;
	135
	136	for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
ba180fd4 JD	137	struct uml_tls_struct* curr =
ba180fd4 JD	138	&task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
aa6758d4	139
ba180fd4 JD	140	/*
	141	* Can't test curr->present, we may need to clear a descriptor
	142	* which had a value.
	143	*/
aa6758d4 PBG	144	if (curr->flushed)
	145	continue;
	146	ret = 1;
	147	break;
	148	}
	149	return ret;
	150	}
	151
ba180fd4 JD	152	/*
ba180fd4 JD	153	* On a newly forked process, the TLS descriptors haven't yet been flushed. So
aa6758d4 PBG	154	* we mark them as such and the first switch_to will do the job.
	155	*/
	156	void clear_flushed_tls(struct task_struct *task)
	157	{
	158	int i;
	159
	160	for (i = GDT_ENTRY_TLS_MIN; i < GDT_ENTRY_TLS_MAX; i++) {
ba180fd4 JD	161	struct uml_tls_struct* curr =
ba180fd4 JD	162	&task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
aa6758d4	163
ba180fd4 JD	164	/*
	165	* Still correct to do this, if it wasn't present on the host it
	166	* will remain as flushed as it was.
	167	*/
aa6758d4 PBG	168	if (!curr->present)
	169	continue;
	170
	171	curr->flushed = 0;
	172	}
	173	}
	174
ba180fd4 JD	175	/*
ba180fd4 JD	176	* In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
3feb8856 PBG	177	* common host process. So this is needed in SKAS0 too.
	178	*
	179	* However, if each thread had a different host process (and this was discussed
	180	* for SMP support) this won't be needed.
	181	*
	182	* And this will not need be used when (and if) we'll add support to the host
ba180fd4 JD	183	* SKAS patch.
ba180fd4 JD	184	*/
3feb8856	185
291248fd	186	int arch_switch_tls(struct task_struct *to)
aa6758d4	187	{
3feb8856 PBG	188	if (!host_supports_tls)
	189	return 0;
	190
ba180fd4 JD	191	/*
ba180fd4 JD	192	* We have no need whatsoever to switch TLS for kernel threads; beyond
54d8d3b5	193	* that, that would also result in us calling os_set_thread_area with
ba180fd4 JD	194	* userspace_pid[cpu] == 0, which gives an error.
ba180fd4 JD	195	*/
54d8d3b5 PBG	196	if (likely(to->mm))
	197	return load_TLS(O_FORCE, to);
	198
	199	return 0;
aa6758d4 PBG	200	}
aa6758d4 PBG	201
aa6758d4 PBG	202	static int set_tls_entry(struct task_struct* task, struct user_desc *info,
	203	int idx, int flushed)
	204	{
	205	struct thread_struct *t = &task->thread;
	206
	207	if (idx < GDT_ENTRY_TLS_MIN \|\| idx > GDT_ENTRY_TLS_MAX)
	208	return -EINVAL;
	209
	210	t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls = *info;
	211	t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present = 1;
	212	t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed = flushed;
	213
	214	return 0;
	215	}
	216
	217	int arch_copy_tls(struct task_struct *new)
	218	{
	219	struct user_desc info;
	220	int idx, ret = -EFAULT;
	221
	222	if (copy_from_user(&info,
243412be	223	(void __user *) UPT_SI(&new->thread.regs.regs),
aa6758d4 PBG	224	sizeof(info)))
	225	goto out;
	226
	227	ret = -EINVAL;
	228	if (LDT_empty(&info))
	229	goto out;
	230
	231	idx = info.entry_number;
	232
	233	ret = set_tls_entry(new, &info, idx, 0);
	234	out:
	235	return ret;
	236	}
	237
	238	/* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */
b2cf7707 JD	239	static int get_tls_entry(struct task_struct task, struct user_desc info,
b2cf7707 JD	240	int idx)
aa6758d4 PBG	241	{
	242	struct thread_struct *t = &task->thread;
	243
	244	if (!t->arch.tls_array)
	245	goto clear;
	246
	247	if (idx < GDT_ENTRY_TLS_MIN \|\| idx > GDT_ENTRY_TLS_MAX)
	248	return -EINVAL;
	249
	250	if (!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].present)
	251	goto clear;
	252
	253	*info = t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].tls;
	254
	255	out:
ba180fd4 JD	256	/*
ba180fd4 JD	257	* Temporary debugging check, to make sure that things have been
aa6758d4 PBG	258	* flushed. This could be triggered if load_TLS() failed.
aa6758d4 PBG	259	*/
ba180fd4 JD	260	if (unlikely(task == current &&
ba180fd4 JD	261	!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) {
aa6758d4 PBG	262	printk(KERN_ERR "get_tls_entry: task with pid %d got here "
	263	"without flushed TLS.", current->pid);
	264	}
	265
	266	return 0;
	267	clear:
ba180fd4 JD	268	/*
ba180fd4 JD	269	* When the TLS entry has not been set, the values read to user in the
aa6758d4 PBG	270	* tls_array are 0 (because it's cleared at boot, see
	271	* arch/i386/kernel/head.S:cpu_gdt_table). Emulate that.
	272	*/
	273	clear_user_desc(info);
	274	info->entry_number = idx;
	275	goto out;
	276	}
	277
2cf09666	278	SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, user_desc)
aa6758d4 PBG	279	{
	280	struct user_desc info;
	281	int idx, ret;
	282
3feb8856 PBG	283	if (!host_supports_tls)
	284	return -ENOSYS;
	285
aa6758d4 PBG	286	if (copy_from_user(&info, user_desc, sizeof(info)))
	287	return -EFAULT;
	288
	289	idx = info.entry_number;
	290
	291	if (idx == -1) {
	292	idx = get_free_idx(current);
	293	if (idx < 0)
	294	return idx;
	295	info.entry_number = idx;
	296	/* Tell the user which slot we chose for him.*/
	297	if (put_user(idx, &user_desc->entry_number))
	298	return -EFAULT;
	299	}
	300
6aa802ce	301	ret = do_set_thread_area(&info);
aa6758d4 PBG	302	if (ret)
	303	return ret;
	304	return set_tls_entry(current, &info, idx, 1);
	305	}
	306
	307	/*
	308	* Perform set_thread_area on behalf of the traced child.
	309	* Note: error handling is not done on the deferred load, and this differ from
	310	* i386. However the only possible error are caused by bugs.
	311	*/
	312	int ptrace_set_thread_area(struct task_struct *child, int idx,
b2cf7707	313	struct user_desc __user *user_desc)
aa6758d4 PBG	314	{
	315	struct user_desc info;
	316
3feb8856 PBG	317	if (!host_supports_tls)
	318	return -EIO;
	319
aa6758d4 PBG	320	if (copy_from_user(&info, user_desc, sizeof(info)))
	321	return -EFAULT;
	322
	323	return set_tls_entry(child, &info, idx, 0);
	324	}
	325
2cf09666	326	SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, user_desc)
aa6758d4 PBG	327	{
	328	struct user_desc info;
	329	int idx, ret;
	330
3feb8856 PBG	331	if (!host_supports_tls)
	332	return -ENOSYS;
	333
aa6758d4 PBG	334	if (get_user(idx, &user_desc->entry_number))
	335	return -EFAULT;
	336
	337	ret = get_tls_entry(current, &info, idx);
	338	if (ret < 0)
	339	goto out;
	340
	341	if (copy_to_user(user_desc, &info, sizeof(info)))
	342	ret = -EFAULT;
	343
	344	out:
	345	return ret;
	346	}
	347
	348	/*
	349	* Perform get_thread_area on behalf of the traced child.
	350	*/
	351	int ptrace_get_thread_area(struct task_struct *child, int idx,
	352	struct user_desc __user *user_desc)
	353	{
	354	struct user_desc info;
	355	int ret;
	356
3feb8856 PBG	357	if (!host_supports_tls)
	358	return -EIO;
	359
aa6758d4 PBG	360	ret = get_tls_entry(child, &info, idx);
	361	if (ret < 0)
	362	goto out;
	363
	364	if (copy_to_user(user_desc, &info, sizeof(info)))
	365	ret = -EFAULT;
	366	out:
	367	return ret;
	368	}
54d8d3b5	369
ba180fd4	370	/*
b8bec829 JD	371	* This code is really i386-only, but it detects and logs x86_64 GDT indexes
b8bec829 JD	372	* if a 32-bit UML is running on a 64-bit host.
ba180fd4	373	*/
65a58ab0 JD	374	static int __init __setup_host_supports_tls(void)
65a58ab0 JD	375	{
3feb8856 PBG	376	check_host_supports_tls(&host_supports_tls, &host_gdt_entry_tls_min);
	377	if (host_supports_tls) {
	378	printk(KERN_INFO "Host TLS support detected\n");
	379	printk(KERN_INFO "Detected host type: ");
	380	switch (host_gdt_entry_tls_min) {
b8bec829 JD	381	case GDT_ENTRY_TLS_MIN_I386:
	382	printk(KERN_CONT "i386");
	383	break;
	384	case GDT_ENTRY_TLS_MIN_X86_64:
	385	printk(KERN_CONT "x86_64");
	386	break;
3feb8856	387	}
b8bec829 JD	388	printk(KERN_CONT " (GDT indexes %d to %d)\n",
	389	host_gdt_entry_tls_min,
	390	host_gdt_entry_tls_min + GDT_ENTRY_TLS_ENTRIES);
3feb8856 PBG	391	} else
	392	printk(KERN_ERR " Host TLS support NOT detected! "
	393	"TLS support inside UML will not work\n");
a5d2f46a	394	return 0;
3feb8856 PBG	395	}
	396
	397	__initcall(__setup_host_supports_tls);