ldt.c revision 4dbf7af6442a9a882855bed0d999659ac413e3ac 
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 *null)
24{
25	if (current->active_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 + 511) & (~511);
39	if (mincount * LDT_ENTRY_SIZE > PAGE_SIZE)
40		newldt = vmalloc(mincount * LDT_ENTRY_SIZE);
41	else
42		newldt = (void *)__get_free_page(GFP_KERNEL);
43
44	if (!newldt)
45		return -ENOMEM;
46
47	if (oldsize)
48		memcpy(newldt, pc->ldt, oldsize * LDT_ENTRY_SIZE);
49	oldldt = pc->ldt;
50	memset(newldt + oldsize * LDT_ENTRY_SIZE, 0,
51	       (mincount - oldsize) * LDT_ENTRY_SIZE);
52
53#ifdef CONFIG_X86_64
54	/* CHECKME: Do we really need this ? */
55	wmb();
56#endif
57	pc->ldt = newldt;
58	wmb();
59	pc->size = mincount;
60	wmb();
61
62	if (reload) {
63#ifdef CONFIG_SMP
64		cpumask_t mask;
65
66		preempt_disable();
67		load_LDT(pc);
68		mask = cpumask_of_cpu(smp_processor_id());
69		if (!cpus_equal(current->mm->cpu_vm_mask, mask))
70			smp_call_function(flush_ldt, NULL, 1, 1);
71		preempt_enable();
72#else
73		load_LDT(pc);
74#endif
75	}
76	if (oldsize) {
77		if (oldsize * LDT_ENTRY_SIZE > PAGE_SIZE)
78			vfree(oldldt);
79		else
80			put_page(virt_to_page(oldldt));
81	}
82	return 0;
83}
84
85static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
86{
87	int err = alloc_ldt(new, old->size, 0);
88
89	if (err < 0)
90		return err;
91	memcpy(new->ldt, old->ldt, old->size * LDT_ENTRY_SIZE);
92	return 0;
93}
94
95/*
96 * we do not have to muck with descriptors here, that is
97 * done in switch_mm() as needed.
98 */
99int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
100{
101	struct mm_struct *old_mm;
102	int retval = 0;
103
104	mutex_init(&mm->context.lock);
105	mm->context.size = 0;
106	old_mm = current->mm;
107	if (old_mm && old_mm->context.size > 0) {
108		mutex_lock(&old_mm->context.lock);
109		retval = copy_ldt(&mm->context, &old_mm->context);
110		mutex_unlock(&old_mm->context.lock);
111	}
112	return retval;
113}
114
115/*
116 * No need to lock the MM as we are the last user
117 *
118 * 64bit: Don't touch the LDT register - we're already in the next thread.
119 */
120void destroy_context(struct mm_struct *mm)
121{
122	if (mm->context.size) {
123#ifdef CONFIG_X86_32
124		/* CHECKME: Can this ever happen ? */
125		if (mm == current->active_mm)
126			clear_LDT();
127#endif
128		if (mm->context.size * LDT_ENTRY_SIZE > PAGE_SIZE)
129			vfree(mm->context.ldt);
130		else
131			put_page(virt_to_page(mm->context.ldt));
132		mm->context.size = 0;
133	}
134}
135
136static int read_ldt(void __user *ptr, unsigned long bytecount)
137{
138	int err;
139	unsigned long size;
140	struct mm_struct *mm = current->mm;
141
142	if (!mm->context.size)
143		return 0;
144	if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
145		bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
146
147	mutex_lock(&mm->context.lock);
148	size = mm->context.size * LDT_ENTRY_SIZE;
149	if (size > bytecount)
150		size = bytecount;
151
152	err = 0;
153	if (copy_to_user(ptr, mm->context.ldt, size))
154		err = -EFAULT;
155	mutex_unlock(&mm->context.lock);
156	if (err < 0)
157		goto error_return;
158	if (size != bytecount) {
159		/* zero-fill the rest */
160		if (clear_user(ptr + size, bytecount - size) != 0) {
161			err = -EFAULT;
162			goto error_return;
163		}
164	}
165	return bytecount;
166error_return:
167	return err;
168}
169
170static int read_default_ldt(void __user *ptr, unsigned long bytecount)
171{
172	/* CHECKME: Can we use _one_ random number ? */
173#ifdef CONFIG_X86_32
174	unsigned long size = 5 * sizeof(struct desc_struct);
175#else
176	unsigned long size = 128;
177#endif
178	if (bytecount > size)
179		bytecount = size;
180	if (clear_user(ptr, bytecount))
181		return -EFAULT;
182	return bytecount;
183}
184
185static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
186{
187	struct mm_struct *mm = current->mm;
188	struct desc_struct ldt;
189	int error;
190	struct user_desc ldt_info;
191
192	error = -EINVAL;
193	if (bytecount != sizeof(ldt_info))
194		goto out;
195	error = -EFAULT;
196	if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
197		goto out;
198
199	error = -EINVAL;
200	if (ldt_info.entry_number >= LDT_ENTRIES)
201		goto out;
202	if (ldt_info.contents == 3) {
203		if (oldmode)
204			goto out;
205		if (ldt_info.seg_not_present == 0)
206			goto out;
207	}
208
209	mutex_lock(&mm->context.lock);
210	if (ldt_info.entry_number >= mm->context.size) {
211		error = alloc_ldt(&current->mm->context,
212				  ldt_info.entry_number + 1, 1);
213		if (error < 0)
214			goto out_unlock;
215	}
216
217	/* Allow LDTs to be cleared by the user. */
218	if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
219		if (oldmode || LDT_empty(&ldt_info)) {
220			memset(&ldt, 0, sizeof(ldt));
221			goto install;
222		}
223	}
224
225	fill_ldt(&ldt, &ldt_info);
226	if (oldmode)
227		ldt.avl = 0;
228
229	/* Install the new entry ...  */
230install:
231	write_ldt_entry(mm->context.ldt, ldt_info.entry_number, &ldt);
232	error = 0;
233
234out_unlock:
235	mutex_unlock(&mm->context.lock);
236out:
237	return error;
238}
239
240asmlinkage int sys_modify_ldt(int func, void __user *ptr,
241			      unsigned long bytecount)
242{
243	int ret = -ENOSYS;
244
245	switch (func) {
246	case 0:
247		ret = read_ldt(ptr, bytecount);
248		break;
249	case 1:
250		ret = write_ldt(ptr, bytecount, 1);
251		break;
252	case 2:
253		ret = read_default_ldt(ptr, bytecount);
254		break;
255	case 0x11:
256		ret = write_ldt(ptr, bytecount, 0);
257		break;
258	}
259	return ret;
260}
261