ldt.c revision b478458aeebfc55fe409abec43794ac72a623c79 
1/*
2 * Copyright (C) 1992 Krishna Balasubramanian and Linus Torvalds
3 * Copyright (C) 1999 Ingo Molnar <mingo@redhat.com>
4 * Copyright (C) 2002 Andi Kleen
5 *
6 * This handles calls from both 32bit and 64bit mode.
7 */
8
9#include <linux/errno.h>
10#include <linux/sched.h>
11#include <linux/string.h>
12#include <linux/mm.h>
13#include <linux/smp.h>
14#include <linux/vmalloc.h>
15
16#include <asm/uaccess.h>
17#include <asm/system.h>
18#include <asm/ldt.h>
19#include <asm/desc.h>
20#include <asm/mmu_context.h>
21
22#ifdef CONFIG_SMP
23static void flush_ldt(void *current_mm)
24{
25	if (current->active_mm == current_mm)
26		load_LDT(&current->active_mm->context);
27}
28#endif
29
30static int alloc_ldt(mm_context_t *pc, int mincount, int reload)
31{
32	void *oldldt, *newldt;
33	int oldsize;
34
35	if (mincount <= pc->size)
36		return 0;
37	oldsize = pc->size;
38	mincount = (mincount + (PAGE_SIZE / LDT_ENTRY_SIZE - 1)) &
39			(~(PAGE_SIZE / LDT_ENTRY_SIZE - 1));
40	if (mincount * LDT_ENTRY_SIZE > PAGE_SIZE)
41		newldt = vmalloc(mincount * LDT_ENTRY_SIZE);
42	else
43		newldt = (void *)__get_free_page(GFP_KERNEL);
44
45	if (!newldt)
46		return -ENOMEM;
47
48	if (oldsize)
49		memcpy(newldt, pc->ldt, oldsize * LDT_ENTRY_SIZE);
50	oldldt = pc->ldt;
51	memset(newldt + oldsize * LDT_ENTRY_SIZE, 0,
52	       (mincount - oldsize) * LDT_ENTRY_SIZE);
53
54#ifdef CONFIG_X86_64
55	/* CHECKME: Do we really need this ? */
56	wmb();
57#endif
58	pc->ldt = newldt;
59	wmb();
60	pc->size = mincount;
61	wmb();
62
63	if (reload) {
64#ifdef CONFIG_SMP
65		cpumask_t mask;
66
67		preempt_disable();
68		load_LDT(pc);
69		mask = cpumask_of_cpu(smp_processor_id());
70		if (!cpus_equal(current->mm->cpu_vm_mask, mask))
71			smp_call_function(flush_ldt, current->mm, 1, 1);
72		preempt_enable();
73#else
74		load_LDT(pc);
75#endif
76	}
77	if (oldsize) {
78		if (oldsize * LDT_ENTRY_SIZE > PAGE_SIZE)
79			vfree(oldldt);
80		else
81			put_page(virt_to_page(oldldt));
82	}
83	return 0;
84}
85
86static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
87{
88	int err = alloc_ldt(new, old->size, 0);
89
90	if (err < 0)
91		return err;
92	memcpy(new->ldt, old->ldt, old->size * LDT_ENTRY_SIZE);
93	return 0;
94}
95
96/*
97 * we do not have to muck with descriptors here, that is
98 * done in switch_mm() as needed.
99 */
100int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
101{
102	struct mm_struct *old_mm;
103	int retval = 0;
104
105	mutex_init(&mm->context.lock);
106	mm->context.size = 0;
107	old_mm = current->mm;
108	if (old_mm && old_mm->context.size > 0) {
109		mutex_lock(&old_mm->context.lock);
110		retval = copy_ldt(&mm->context, &old_mm->context);
111		mutex_unlock(&old_mm->context.lock);
112	}
113	return retval;
114}
115
116/*
117 * No need to lock the MM as we are the last user
118 *
119 * 64bit: Don't touch the LDT register - we're already in the next thread.
120 */
121void destroy_context(struct mm_struct *mm)
122{
123	if (mm->context.size) {
124#ifdef CONFIG_X86_32
125		/* CHECKME: Can this ever happen ? */
126		if (mm == current->active_mm)
127			clear_LDT();
128#endif
129		if (mm->context.size * LDT_ENTRY_SIZE > PAGE_SIZE)
130			vfree(mm->context.ldt);
131		else
132			put_page(virt_to_page(mm->context.ldt));
133		mm->context.size = 0;
134	}
135}
136
137static int read_ldt(void __user *ptr, unsigned long bytecount)
138{
139	int err;
140	unsigned long size;
141	struct mm_struct *mm = current->mm;
142
143	if (!mm->context.size)
144		return 0;
145	if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
146		bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
147
148	mutex_lock(&mm->context.lock);
149	size = mm->context.size * LDT_ENTRY_SIZE;
150	if (size > bytecount)
151		size = bytecount;
152
153	err = 0;
154	if (copy_to_user(ptr, mm->context.ldt, size))
155		err = -EFAULT;
156	mutex_unlock(&mm->context.lock);
157	if (err < 0)
158		goto error_return;
159	if (size != bytecount) {
160		/* zero-fill the rest */
161		if (clear_user(ptr + size, bytecount - size) != 0) {
162			err = -EFAULT;
163			goto error_return;
164		}
165	}
166	return bytecount;
167error_return:
168	return err;
169}
170
171static int read_default_ldt(void __user *ptr, unsigned long bytecount)
172{
173	/* CHECKME: Can we use _one_ random number ? */
174#ifdef CONFIG_X86_32
175	unsigned long size = 5 * sizeof(struct desc_struct);
176#else
177	unsigned long size = 128;
178#endif
179	if (bytecount > size)
180		bytecount = size;
181	if (clear_user(ptr, bytecount))
182		return -EFAULT;
183	return bytecount;
184}
185
186static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
187{
188	struct mm_struct *mm = current->mm;
189	struct desc_struct ldt;
190	int error;
191	struct user_desc ldt_info;
192
193	error = -EINVAL;
194	if (bytecount != sizeof(ldt_info))
195		goto out;
196	error = -EFAULT;
197	if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
198		goto out;
199
200	error = -EINVAL;
201	if (ldt_info.entry_number >= LDT_ENTRIES)
202		goto out;
203	if (ldt_info.contents == 3) {
204		if (oldmode)
205			goto out;
206		if (ldt_info.seg_not_present == 0)
207			goto out;
208	}
209
210	mutex_lock(&mm->context.lock);
211	if (ldt_info.entry_number >= mm->context.size) {
212		error = alloc_ldt(&current->mm->context,
213				  ldt_info.entry_number + 1, 1);
214		if (error < 0)
215			goto out_unlock;
216	}
217
218	/* Allow LDTs to be cleared by the user. */
219	if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
220		if (oldmode || LDT_empty(&ldt_info)) {
221			memset(&ldt, 0, sizeof(ldt));
222			goto install;
223		}
224	}
225
226	fill_ldt(&ldt, &ldt_info);
227	if (oldmode)
228		ldt.avl = 0;
229
230	/* Install the new entry ...  */
231install:
232	write_ldt_entry(mm->context.ldt, ldt_info.entry_number, &ldt);
233	error = 0;
234
235out_unlock:
236	mutex_unlock(&mm->context.lock);
237out:
238	return error;
239}
240
241asmlinkage int sys_modify_ldt(int func, void __user *ptr,
242			      unsigned long bytecount)
243{
244	int ret = -ENOSYS;
245
246	switch (func) {
247	case 0:
248		ret = read_ldt(ptr, bytecount);
249		break;
250	case 1:
251		ret = write_ldt(ptr, bytecount, 1);
252		break;
253	case 2:
254		ret = read_default_ldt(ptr, bytecount);
255		break;
256	case 0x11:
257		ret = write_ldt(ptr, bytecount, 0);
258		break;
259	}
260	return ret;
261}
262