aboutsummaryrefslogtreecommitdiffstats
path: root/arch/x86/kernel/ldt.c
blob: 3fee2aa50f3f63d594304611090338d36f3fcc01 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
/*
 * Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
 * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
 * Copyright (C) 2002 Andi Kleen
 *
 * This handles calls from both 32bit and 64bit mode.
 */

#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/vmalloc.h>

#include <asm/uaccess.h>
#include <asm/system.h>
#include <asm/ldt.h>
#include <asm/desc.h>
#include <asm/mmu_context.h>

#ifdef CONFIG_SMP
static void flush_ldt(void *current_mm)
{
	if (current->active_mm == current_mm)
		load_LDT(&current->active_mm->context);
}
#endif

static int alloc_ldt(mm_context_t *pc, int mincount, int reload)
{
	void *oldldt, *newldt;
	int oldsize;

	if (mincount <= pc->size)
		return 0;
	oldsize = pc->size;
	mincount = (mincount + (PAGE_SIZE / LDT_ENTRY_SIZE - 1)) &
			(~(PAGE_SIZE / LDT_ENTRY_SIZE - 1));
	if (mincount * LDT_ENTRY_SIZE > PAGE_SIZE)
		newldt = vmalloc(mincount * LDT_ENTRY_SIZE);
	else
		newldt = (void *)__get_free_page(GFP_KERNEL);

	if (!newldt)
		return -ENOMEM;

	if (oldsize)
		memcpy(newldt, pc->ldt, oldsize * LDT_ENTRY_SIZE);
	oldldt = pc->ldt;
	memset(newldt + oldsize * LDT_ENTRY_SIZE, 0,
	       (mincount - oldsize) * LDT_ENTRY_SIZE);

#ifdef CONFIG_X86_64
	/* CHECKME: Do we really need this ? */
	wmb();
#endif
	pc->ldt = newldt;
	wmb();
	pc->size = mincount;
	wmb();

	if (reload) {
#ifdef CONFIG_SMP
		cpumask_of_cpu_ptr_declare(mask);

		preempt_disable();
		load_LDT(pc);
		cpumask_of_cpu_ptr_next(mask, smp_processor_id());
		if (!cpus_equal(current->mm->cpu_vm_mask, *mask))
			smp_call_function(flush_ldt, current->mm, 1);
		preempt_enable();
#else
		load_LDT(pc);
#endif
	}
	if (oldsize) {
		if (oldsize * LDT_ENTRY_SIZE > PAGE_SIZE)
			vfree(oldldt);
		else
			put_page(virt_to_page(oldldt));
	}
	return 0;
}

static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
{
	int err = alloc_ldt(new, old->size, 0);

	if (err < 0)
		return err;
	memcpy(new->ldt, old->ldt, old->size * LDT_ENTRY_SIZE);
	return 0;
}

/*
 * we do not have to muck with descriptors here, that is
 * done in switch_mm() as needed.
 */
int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
{
	struct mm_struct *old_mm;
	int retval = 0;

	mutex_init(&mm->context.lock);
	mm->context.size = 0;
	old_mm = current->mm;
	if (old_mm && old_mm->context.size > 0) {
		mutex_lock(&old_mm->context.lock);
		retval = copy_ldt(&mm->context, &old_mm->context);
		mutex_unlock(&old_mm->context.lock);
	}
	return retval;
}

/*
 * No need to lock the MM as we are the last user
 *
 * 64bit: Don't touch the LDT register - we're already in the next thread.
 */
void destroy_context(struct mm_struct *mm)
{
	if (mm->context.size) {
#ifdef CONFIG_X86_32
		/* CHECKME: Can this ever happen ? */
		if (mm == current->active_mm)
			clear_LDT();
#endif
		if (mm->context.size * LDT_ENTRY_SIZE > PAGE_SIZE)
			vfree(mm->context.ldt);
		else
			put_page(virt_to_page(mm->context.ldt));
		mm->context.size = 0;
	}
}

static int read_ldt(void __user *ptr, unsigned long bytecount)
{
	int err;
	unsigned long size;
	struct mm_struct *mm = current->mm;

	if (!mm->context.size)
		return 0;
	if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
		bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;

	mutex_lock(&mm->context.lock);
	size = mm->context.size * LDT_ENTRY_SIZE;
	if (size > bytecount)
		size = bytecount;

	err = 0;
	if (copy_to_user(ptr, mm->context.ldt, size))
		err = -EFAULT;
	mutex_unlock(&mm->context.lock);
	if (err < 0)
		goto error_return;
	if (size != bytecount) {
		/* zero-fill the rest */
		if (clear_user(ptr + size, bytecount - size) != 0) {
			err = -EFAULT;
			goto error_return;
		}
	}
	return bytecount;
error_return:
	return err;
}

static int read_default_ldt(void __user *ptr, unsigned long bytecount)
{
	/* CHECKME: Can we use _one_ random number ? */
#ifdef CONFIG_X86_32
	unsigned long size = 5 * sizeof(struct desc_struct);
#else
	unsigned long size = 128;
#endif
	if (bytecount > size)
		bytecount = size;
	if (clear_user(ptr, bytecount))
		return -EFAULT;
	return bytecount;
}

static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
{
	struct mm_struct *mm = current->mm;
	struct desc_struct ldt;
	int error;
	struct user_desc ldt_info;

	error = -EINVAL;
	if (bytecount != sizeof(ldt_info))
		goto out;
	error = -EFAULT;
	if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
		goto out;

	error = -EINVAL;
	if (ldt_info.entry_number >= LDT_ENTRIES)
		goto out;
	if (ldt_info.contents == 3) {
		if (oldmode)
			goto out;
		if (ldt_info.seg_not_present == 0)
			goto out;
	}

	mutex_lock(&mm->context.lock);
	if (ldt_info.entry_number >= mm->context.size) {
		error = alloc_ldt(&current->mm->context,
				  ldt_info.entry_number + 1, 1);
		if (error < 0)
			goto out_unlock;
	}

	/* Allow LDTs to be cleared by the user. */
	if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
		if (oldmode || LDT_empty(&ldt_info)) {
			memset(&ldt, 0, sizeof(ldt));
			goto install;
		}
	}

	fill_ldt(&ldt, &ldt_info);
	if (oldmode)
		ldt.avl = 0;

	/* Install the new entry ...  */
install:
	write_ldt_entry(mm->context.ldt, ldt_info.entry_number, &ldt);
	error = 0;

out_unlock:
	mutex_unlock(&mm->context.lock);
out:
	return error;
}

asmlinkage int sys_modify_ldt(int func, void __user *ptr,
			      unsigned long bytecount)
{
	int ret = -ENOSYS;

	switch (func) {
	case 0:
		ret = read_ldt(ptr, bytecount);
		break;
	case 1:
		ret = write_ldt(ptr, bytecount, 1);
		break;
	case 2:
		ret = read_default_ldt(ptr, bytecount);
		break;
	case 0x11:
		ret = write_ldt(ptr, bytecount, 0);
		break;
	}
	return ret;
}

Privacy Policy