ldt.c revision 7ed6fb9b5a5510e4ef78ab27419184741169978a 
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
23#ifdef CONFIG_SMP
24static void flush_ldt(void *current_mm)
25{
26	if (current->active_mm == current_mm)
27		load_LDT(&current->active_mm->context);
28}
29#endif
30
31static int alloc_ldt(mm_context_t *pc, int mincount, int reload)
32{
33	void *oldldt, *newldt;
34	int oldsize;
35
36	if (mincount <= pc->size)
37		return 0;
38	oldsize = pc->size;
39	mincount = (mincount + (PAGE_SIZE / LDT_ENTRY_SIZE - 1)) &
40			(~(PAGE_SIZE / LDT_ENTRY_SIZE - 1));
41	if (mincount * LDT_ENTRY_SIZE > PAGE_SIZE)
42		newldt = vmalloc(mincount * LDT_ENTRY_SIZE);
43	else
44		newldt = (void *)__get_free_page(GFP_KERNEL);
45
46	if (!newldt)
47		return -ENOMEM;
48
49	if (oldsize)
50		memcpy(newldt, pc->ldt, oldsize * LDT_ENTRY_SIZE);
51	oldldt = pc->ldt;
52	memset(newldt + oldsize * LDT_ENTRY_SIZE, 0,
53	       (mincount - oldsize) * LDT_ENTRY_SIZE);
54
55	paravirt_alloc_ldt(newldt, mincount);
56
57#ifdef CONFIG_X86_64
58	/* CHECKME: Do we really need this ? */
59	wmb();
60#endif
61	pc->ldt = newldt;
62	wmb();
63	pc->size = mincount;
64	wmb();
65
66	if (reload) {
67#ifdef CONFIG_SMP
68		preempt_disable();
69		load_LDT(pc);
70		if (!cpumask_equal(mm_cpumask(current->mm),
71				   cpumask_of(smp_processor_id())))
72			smp_call_function(flush_ldt, current->mm, 1);
73		preempt_enable();
74#else
75		load_LDT(pc);
76#endif
77	}
78	if (oldsize) {
79		paravirt_free_ldt(oldldt, oldsize);
80		if (oldsize * LDT_ENTRY_SIZE > PAGE_SIZE)
81			vfree(oldldt);
82		else
83			put_page(virt_to_page(oldldt));
84	}
85	return 0;
86}
87
88static inline int copy_ldt(mm_context_t *new, mm_context_t *old)
89{
90	int err = alloc_ldt(new, old->size, 0);
91	int i;
92
93	if (err < 0)
94		return err;
95
96	for (i = 0; i < old->size; i++)
97		write_ldt_entry(new->ldt, i, old->ldt + i * LDT_ENTRY_SIZE);
98	return 0;
99}
100
101/*
102 * we do not have to muck with descriptors here, that is
103 * done in switch_mm() as needed.
104 */
105int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
106{
107	struct mm_struct *old_mm;
108	int retval = 0;
109
110	mutex_init(&mm->context.lock);
111	mm->context.size = 0;
112	old_mm = current->mm;
113	if (old_mm && old_mm->context.size > 0) {
114		mutex_lock(&old_mm->context.lock);
115		retval = copy_ldt(&mm->context, &old_mm->context);
116		mutex_unlock(&old_mm->context.lock);
117	}
118	return retval;
119}
120
121/*
122 * No need to lock the MM as we are the last user
123 *
124 * 64bit: Don't touch the LDT register - we're already in the next thread.
125 */
126void destroy_context(struct mm_struct *mm)
127{
128	if (mm->context.size) {
129#ifdef CONFIG_X86_32
130		/* CHECKME: Can this ever happen ? */
131		if (mm == current->active_mm)
132			clear_LDT();
133#endif
134		paravirt_free_ldt(mm->context.ldt, mm->context.size);
135		if (mm->context.size * LDT_ENTRY_SIZE > PAGE_SIZE)
136			vfree(mm->context.ldt);
137		else
138			put_page(virt_to_page(mm->context.ldt));
139		mm->context.size = 0;
140	}
141}
142
143static int read_ldt(void __user *ptr, unsigned long bytecount)
144{
145	int err;
146	unsigned long size;
147	struct mm_struct *mm = current->mm;
148
149	if (!mm->context.size)
150		return 0;
151	if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
152		bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
153
154	mutex_lock(&mm->context.lock);
155	size = mm->context.size * LDT_ENTRY_SIZE;
156	if (size > bytecount)
157		size = bytecount;
158
159	err = 0;
160	if (copy_to_user(ptr, mm->context.ldt, size))
161		err = -EFAULT;
162	mutex_unlock(&mm->context.lock);
163	if (err < 0)
164		goto error_return;
165	if (size != bytecount) {
166		/* zero-fill the rest */
167		if (clear_user(ptr + size, bytecount - size) != 0) {
168			err = -EFAULT;
169			goto error_return;
170		}
171	}
172	return bytecount;
173error_return:
174	return err;
175}
176
177static int read_default_ldt(void __user *ptr, unsigned long bytecount)
178{
179	/* CHECKME: Can we use _one_ random number ? */
180#ifdef CONFIG_X86_32
181	unsigned long size = 5 * sizeof(struct desc_struct);
182#else
183	unsigned long size = 128;
184#endif
185	if (bytecount > size)
186		bytecount = size;
187	if (clear_user(ptr, bytecount))
188		return -EFAULT;
189	return bytecount;
190}
191
192static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
193{
194	struct mm_struct *mm = current->mm;
195	struct desc_struct ldt;
196	int error;
197	struct user_desc ldt_info;
198
199	error = -EINVAL;
200	if (bytecount != sizeof(ldt_info))
201		goto out;
202	error = -EFAULT;
203	if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
204		goto out;
205
206	error = -EINVAL;
207	if (ldt_info.entry_number >= LDT_ENTRIES)
208		goto out;
209	if (ldt_info.contents == 3) {
210		if (oldmode)
211			goto out;
212		if (ldt_info.seg_not_present == 0)
213			goto out;
214	}
215
216	mutex_lock(&mm->context.lock);
217	if (ldt_info.entry_number >= mm->context.size) {
218		error = alloc_ldt(&current->mm->context,
219				  ldt_info.entry_number + 1, 1);
220		if (error < 0)
221			goto out_unlock;
222	}
223
224	/* Allow LDTs to be cleared by the user. */
225	if (ldt_info.base_addr == 0 && ldt_info.limit == 0) {
226		if (oldmode || LDT_empty(&ldt_info)) {
227			memset(&ldt, 0, sizeof(ldt));
228			goto install;
229		}
230	}
231
232	/*
233	 * On x86-64 we do not support 16-bit segments due to
234	 * IRET leaking the high bits of the kernel stack address.
235	 */
236#ifdef CONFIG_X86_64
237	if (!ldt_info.seg_32bit) {
238		error = -EINVAL;
239		goto out_unlock;
240	}
241#endif
242
243	fill_ldt(&ldt, &ldt_info);
244	if (oldmode)
245		ldt.avl = 0;
246
247	/* Install the new entry ...  */
248install:
249	write_ldt_entry(mm->context.ldt, ldt_info.entry_number, &ldt);
250	error = 0;
251
252out_unlock:
253	mutex_unlock(&mm->context.lock);
254out:
255	return error;
256}
257
258asmlinkage int sys_modify_ldt(int func, void __user *ptr,
259			      unsigned long bytecount)
260{
261	int ret = -ENOSYS;
262
263	switch (func) {
264	case 0:
265		ret = read_ldt(ptr, bytecount);
266		break;
267	case 1:
268		ret = write_ldt(ptr, bytecount, 1);
269		break;
270	case 2:
271		ret = read_default_ldt(ptr, bytecount);
272		break;
273	case 0x11:
274		ret = write_ldt(ptr, bytecount, 0);
275		break;
276	}
277	return ret;
278}
279