[mirror_ubuntu-focal-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 <linux/uaccess.h>
#include <asm/ptrace-abi.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_set_tls(struct task_struct *new, unsigned long tls)
{
	struct user_desc info;
	int idx, ret = -EFAULT;

	if (copy_from_user(&info, (void __user *) tls, 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>
7c0f6ba6	9	#include <linux/uaccess.h>
da028d5e	10	#include <asm/ptrace-abi.h>
37185b33 AV	11	#include <os.h>
	12	#include <skas.h>
	13	#include <sysdep/tls.h>
aa6758d4	14
65a58ab0 JD	15	/*
	16	* If needed we can detect when it's uninitialized.
	17	*
	18	* These are initialized in an initcall and unchanged thereafter.
	19	*/
3feb8856	20	static int host_supports_tls = -1;
65a58ab0	21	int host_gdt_entry_tls_min;
3feb8856	22
6aa802ce	23	int do_set_thread_area(struct user_desc *info)
aa6758d4 PBG	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();
b8bec829 JD	31
	32	if (ret)
	33	printk(KERN_ERR "PTRACE_SET_THREAD_AREA failed, err = %d, "
	34	"index = %d\n", ret, info->entry_number);
	35
aa6758d4 PBG	36	return ret;
	37	}
	38
6aa802ce	39	int do_get_thread_area(struct user_desc *info)
aa6758d4 PBG	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();
b8bec829 JD	47
	48	if (ret)
	49	printk(KERN_ERR "PTRACE_GET_THREAD_AREA failed, err = %d, "
	50	"index = %d\n", ret, info->entry_number);
	51
aa6758d4 PBG	52	return ret;
aa6758d4 PBG	53	}
aa6758d4 PBG	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	*
b60745b9	60	* Also, this must be tested when compiling in SKAS mode with dynamic linking
aa6758d4 PBG	61	* and running against NPTL.
	62	*/
	63	static 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
aa6758d4 PBG	77	static inline void clear_user_desc(struct user_desc* info)
	78	{
	79	/* Postcondition: LDT_empty(info) returns true. */
	80	memset(info, 0, sizeof(*info));
	81
ba180fd4 JD	82	/*
ba180fd4 JD	83	* Check the LDT_empty or the i386 sys_get_thread_area code - we obtain
aa6758d4 PBG	84	* indeed an empty user_desc.
	85	*/
	86	info->read_exec_only = 1;
	87	info->seg_not_present = 1;
	88	}
	89
54d8d3b5 PBG	90	#define O_FORCE 1
54d8d3b5 PBG	91
aa6758d4 PBG	92	static 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++) {
ba180fd4 JD	98	struct uml_tls_struct* curr =
ba180fd4 JD	99	&to->thread.arch.tls_array[idx - GDT_ENTRY_TLS_MIN];
aa6758d4	100
ba180fd4 JD	101	/*
	102	* Actually, now if it wasn't flushed it gets cleared and
	103	* flushed to the host, which will clear it.
	104	*/
aa6758d4 PBG	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	}
	124	out:
	125	return ret;
	126	}
	127
ba180fd4 JD	128	/*
ba180fd4 JD	129	* Verify if we need to do a flush for the new process, i.e. if there are any
aa6758d4 PBG	130	* present desc's, only if they haven't been flushed.
	131	*/
	132	static 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++) {
ba180fd4 JD	138	struct uml_tls_struct* curr =
ba180fd4 JD	139	&task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
aa6758d4	140
ba180fd4 JD	141	/*
	142	* Can't test curr->present, we may need to clear a descriptor
	143	* which had a value.
	144	*/
aa6758d4 PBG	145	if (curr->flushed)
	146	continue;
	147	ret = 1;
	148	break;
	149	}
	150	return ret;
	151	}
	152
ba180fd4 JD	153	/*
ba180fd4 JD	154	* On a newly forked process, the TLS descriptors haven't yet been flushed. So
aa6758d4 PBG	155	* we mark them as such and the first switch_to will do the job.
	156	*/
	157	void 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++) {
ba180fd4 JD	162	struct uml_tls_struct* curr =
ba180fd4 JD	163	&task->thread.arch.tls_array[i - GDT_ENTRY_TLS_MIN];
aa6758d4	164
ba180fd4 JD	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	*/
aa6758d4 PBG	169	if (!curr->present)
	170	continue;
	171
	172	curr->flushed = 0;
	173	}
	174	}
	175
ba180fd4 JD	176	/*
ba180fd4 JD	177	* In SKAS0 mode, currently, multiple guest threads sharing the same ->mm have a
3feb8856 PBG	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
ba180fd4 JD	184	* SKAS patch.
ba180fd4 JD	185	*/
3feb8856	186
291248fd	187	int arch_switch_tls(struct task_struct *to)
aa6758d4	188	{
3feb8856 PBG	189	if (!host_supports_tls)
	190	return 0;
	191
ba180fd4 JD	192	/*
ba180fd4 JD	193	* We have no need whatsoever to switch TLS for kernel threads; beyond
54d8d3b5	194	* that, that would also result in us calling os_set_thread_area with
ba180fd4 JD	195	* userspace_pid[cpu] == 0, which gives an error.
ba180fd4 JD	196	*/
54d8d3b5 PBG	197	if (likely(to->mm))
	198	return load_TLS(O_FORCE, to);
	199
	200	return 0;
aa6758d4 PBG	201	}
aa6758d4 PBG	202
aa6758d4 PBG	203	static 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
89d8047b	218	int arch_set_tls(struct task_struct *new, unsigned long tls)
aa6758d4 PBG	219	{
	220	struct user_desc info;
	221	int idx, ret = -EFAULT;
	222
89d8047b	223	if (copy_from_user(&info, (void __user *) tls, sizeof(info)))
aa6758d4 PBG	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);
	233	out:
	234	return ret;
	235	}
	236
	237	/* XXX: use do_get_thread_area to read the host value? I'm not at all sure! */
b2cf7707 JD	238	static int get_tls_entry(struct task_struct task, struct user_desc info,
b2cf7707 JD	239	int idx)
aa6758d4 PBG	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
	254	out:
ba180fd4 JD	255	/*
ba180fd4 JD	256	* Temporary debugging check, to make sure that things have been
aa6758d4 PBG	257	* flushed. This could be triggered if load_TLS() failed.
aa6758d4 PBG	258	*/
ba180fd4 JD	259	if (unlikely(task == current &&
ba180fd4 JD	260	!t->arch.tls_array[idx - GDT_ENTRY_TLS_MIN].flushed)) {
aa6758d4 PBG	261	printk(KERN_ERR "get_tls_entry: task with pid %d got here "
	262	"without flushed TLS.", current->pid);
	263	}
	264
	265	return 0;
	266	clear:
ba180fd4 JD	267	/*
ba180fd4 JD	268	* When the TLS entry has not been set, the values read to user in the
aa6758d4 PBG	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
2cf09666	277	SYSCALL_DEFINE1(set_thread_area, struct user_desc __user *, user_desc)
aa6758d4 PBG	278	{
	279	struct user_desc info;
	280	int idx, ret;
	281
3feb8856 PBG	282	if (!host_supports_tls)
	283	return -ENOSYS;
	284
aa6758d4 PBG	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
6aa802ce	300	ret = do_set_thread_area(&info);
aa6758d4 PBG	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	*/
	311	int ptrace_set_thread_area(struct task_struct *child, int idx,
b2cf7707	312	struct user_desc __user *user_desc)
aa6758d4 PBG	313	{
	314	struct user_desc info;
	315
3feb8856 PBG	316	if (!host_supports_tls)
	317	return -EIO;
	318
aa6758d4 PBG	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
2cf09666	325	SYSCALL_DEFINE1(get_thread_area, struct user_desc __user *, user_desc)
aa6758d4 PBG	326	{
	327	struct user_desc info;
	328	int idx, ret;
	329
3feb8856 PBG	330	if (!host_supports_tls)
	331	return -ENOSYS;
	332
aa6758d4 PBG	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
	343	out:
	344	return ret;
	345	}
	346
	347	/*
	348	* Perform get_thread_area on behalf of the traced child.
	349	*/
	350	int 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
3feb8856 PBG	356	if (!host_supports_tls)
	357	return -EIO;
	358
aa6758d4 PBG	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;
	365	out:
	366	return ret;
	367	}
54d8d3b5	368
ba180fd4	369	/*
b8bec829 JD	370	* This code is really i386-only, but it detects and logs x86_64 GDT indexes
b8bec829 JD	371	* if a 32-bit UML is running on a 64-bit host.
ba180fd4	372	*/
65a58ab0 JD	373	static int __init __setup_host_supports_tls(void)
65a58ab0 JD	374	{
3feb8856 PBG	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) {
b8bec829 JD	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;
3feb8856	386	}
b8bec829 JD	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);
3feb8856 PBG	390	} else
	391	printk(KERN_ERR " Host TLS support NOT detected! "
	392	"TLS support inside UML will not work\n");
a5d2f46a	393	return 0;
3feb8856 PBG	394	}
	395
	396	__initcall(__setup_host_supports_tls);