ldt.c revision fa81511bb0bbb2b1aace3695ce869da9762624ff 
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/gfp.h>
11#include <linux/sched.h>
12#include <linux/string.h>
13#include <linux/mm.h>
14#include <linux/smp.h>
15#include <linux/vmalloc.h>
16#include <linux/uaccess.h>
17
18#include <asm/ldt.h>
19#include <asm/desc.h>
20#include <asm/mmu_context.h>
21#include <asm/syscalls.h>
22
23int sysctl_ldt16 = 0;
24
25#ifdef CONFIG_SMP
26static void flush_ldt(void *current_mm)
27{
28	if (current->active_mm == current_mm)
29		load_LDT(&current->active_mm->context);
30}
31#endif
32
33static int alloc_ldt(mm_context_t *pc, int mincount, int reload)
34{
35	void *oldldt, *newldt;
36	int oldsize;
37
38	if (mincount <= pc->size)
39		return 0;
40	oldsize = pc->size;
41	mincount = (mincount + (PAGE_SIZE / LDT_ENTRY_SIZE - 1)) &
42			(~(PAGE_SIZE / LDT_ENTRY_SIZE - 1));
43	if (mincount * LDT_ENTRY_SIZE > PAGE_SIZE)
44		newldt = vmalloc(mincount * LDT_ENTRY_SIZE);
45	else
46		newldt = (void *)__get_free_page(GFP_KERNEL);
47
48	if (!newldt)
49		return -ENOMEM;
50
51	if (oldsize)
52		memcpy(newldt, pc->ldt, oldsize * LDT_ENTRY_SIZE);
53	oldldt = pc->ldt;
54	memset(newldt + oldsize * LDT_ENTRY_SIZE, 0,
55	       (mincount - oldsize) * LDT_ENTRY_SIZE);
56
57	paravirt_alloc_ldt(newldt, mincount);
58
59#ifdef CONFIG_X86_64
60	/* CHECKME: Do we really need this ? */
61	wmb();
62#endif
63	pc->ldt = newldt;
64	wmb();
65	pc->size = mincount;
66	wmb();
67
68	if (reload) {
69#ifdef CONFIG_SMP
70		preempt_disable();
71		load_LDT(pc);
72		if (!cpumask_equal(mm_cpumask(current->mm),
73				   cpumask_of(smp_processor_id())))
74			smp_call_function(flush_ldt, current->mm, 1);
75		preempt_enable();
76#else
77		load_LDT(pc);
78#endif
79	}
80	if (oldsize) {
81		paravirt_free_ldt(oldldt, oldsize);
82		if (oldsize * LDT_ENTRY_SIZE > PAGE_SIZE)
83			vfree(oldldt);
84		else
85			put_page(virt_to_page(oldldt));
86	}
87	return 0;
88}
89
90static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
91{
92	int err = alloc_ldt(new, old->size, 0);
93	int i;
94
95	if (err < 0)
96		return err;
97
98	for (i = 0; i < old->size; i++)
99		write_ldt_entry(new->ldt, i, old->ldt + i * LDT_ENTRY_SIZE);
100	return 0;
101}
102
103/*
104 * we do not have to muck with descriptors here, that is
105 * done in switch_mm() as needed.
106 */
107int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
108{
109	struct mm_struct *old_mm;
110	int retval = 0;
111
112	mutex_init(&mm->context.lock);
113	mm->context.size = 0;
114	old_mm = current->mm;
115	if (old_mm && old_mm->context.size > 0) {
116		mutex_lock(&old_mm->context.lock);
117		retval = copy_ldt(&mm->context, &old_mm->context);
118		mutex_unlock(&old_mm->context.lock);
119	}
120	return retval;
121}
122
123/*
124 * No need to lock the MM as we are the last user
125 *
126 * 64bit: Don't touch the LDT register - we're already in the next thread.
127 */
128void destroy_context(struct mm_struct *mm)
129{
130	if (mm->context.size) {
131#ifdef CONFIG_X86_32
132		/* CHECKME: Can this ever happen ? */
133		if (mm == current->active_mm)
134			clear_LDT();
135#endif
136		paravirt_free_ldt(mm->context.ldt, mm->context.size);
137		if (mm->context.size * LDT_ENTRY_SIZE > PAGE_SIZE)
138			vfree(mm->context.ldt);
139		else
140			put_page(virt_to_page(mm->context.ldt));
141		mm->context.size = 0;
142	}
143}
144
145static int read_ldt(void __user *ptr, unsigned long bytecount)
146{
147	int err;
148	unsigned long size;
149	struct mm_struct *mm = current->mm;
150
151	if (!mm->context.size)
152		return 0;
153	if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
154		bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
155
156	mutex_lock(&mm->context.lock);
157	size = mm->context.size * LDT_ENTRY_SIZE;
158	if (size > bytecount)
159		size = bytecount;
160
161	err = 0;
162	if (copy_to_user(ptr, mm->context.ldt, size))
163		err = -EFAULT;
164	mutex_unlock(&mm->context.lock);
165	if (err < 0)
166		goto error_return;
167	if (size != bytecount) {
168		/* zero-fill the rest */
169		if (clear_user(ptr + size, bytecount - size) != 0) {
170			err = -EFAULT;
171			goto error_return;
172		}
173	}
174	return bytecount;
175error_return:
176	return err;
177}
178
179static int read_default_ldt(void __user *ptr, unsigned long bytecount)
180{
181	/* CHECKME: Can we use _one_ random number ? */
182#ifdef CONFIG_X86_32
183	unsigned long size = 5 * sizeof(struct desc_struct);
184#else
185	unsigned long size = 128;
186#endif
187	if (bytecount > size)
188		bytecount = size;
189	if (clear_user(ptr, bytecount))
190		return -EFAULT;
191	return bytecount;
192}
193
194static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
195{
196	struct mm_struct *mm = current->mm;
197	struct desc_struct ldt;
198	int error;
199	struct user_desc ldt_info;
200
201	error = -EINVAL;
202	if (bytecount != sizeof(ldt_info))
203		goto out;
204	error = -EFAULT;
205	if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
206		goto out;
207
208	error = -EINVAL;
209	if (ldt_info.entry_number >= LDT_ENTRIES)
210		goto out;
211	if (ldt_info.contents == 3) {
212		if (oldmode)
213			goto out;
214		if (ldt_info.seg_not_present == 0)
215			goto out;
216	}
217
218	mutex_lock(&mm->context.lock);
219	if (ldt_info.entry_number >= mm->context.size) {
220		error = alloc_ldt(&current->mm->context,
221				  ldt_info.entry_number + 1, 1);
222		if (error < 0)
223			goto out_unlock;
224	}
225
226	/* Allow LDTs to be cleared by the user. */
227	if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
228		if (oldmode || LDT_empty(&ldt_info)) {
229			memset(&ldt, 0, sizeof(ldt));
230			goto install;
231		}
232	}
233
234	/*
235	 * On x86-64 we do not support 16-bit segments due to
236	 * IRET leaking the high bits of the kernel stack address.
237	 */
238#ifdef CONFIG_X86_64
239	if (!ldt_info.seg_32bit && !sysctl_ldt16) {
240		error = -EINVAL;
241		goto out_unlock;
242	}
243#endif
244
245	fill_ldt(&ldt, &ldt_info);
246	if (oldmode)
247		ldt.avl = 0;
248
249	/* Install the new entry ...  */
250install:
251	write_ldt_entry(mm->context.ldt, ldt_info.entry_number, &ldt);
252	error = 0;
253
254out_unlock:
255	mutex_unlock(&mm->context.lock);
256out:
257	return error;
258}
259
260asmlinkage int sys_modify_ldt(int func, void __user *ptr,
261			      unsigned long bytecount)
262{
263	int ret = -ENOSYS;
264
265	switch (func) {
266	case 0:
267		ret = read_ldt(ptr, bytecount);
268		break;
269	case 1:
270		ret = write_ldt(ptr, bytecount, 1);
271		break;
272	case 2:
273		ret = read_default_ldt(ptr, bytecount);
274		break;
275	case 0x11:
276		ret = write_ldt(ptr, bytecount, 0);
277		break;
278	}
279	return ret;
280}
281