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/slab.h>
16#include <linux/vmalloc.h>
17#include <linux/uaccess.h>
18
19#include <asm/ldt.h>
20#include <asm/desc.h>
21#include <asm/mmu_context.h>
22#include <asm/syscalls.h>
23
24/* context.lock is held for us, so we don't need any locking. */
25static void flush_ldt(void *current_mm)
26{
27	mm_context_t *pc;
28
29	if (current->active_mm != current_mm)
30		return;
31
32	pc = &current->active_mm->context;
33	set_ldt(pc->ldt->entries, pc->ldt->size);
34}
35
36/* The caller must call finalize_ldt_struct on the result. LDT starts zeroed. */
37static struct ldt_struct *alloc_ldt_struct(int size)
38{
39	struct ldt_struct *new_ldt;
40	int alloc_size;
41
42	if (size > LDT_ENTRIES)
43		return NULL;
44
45	new_ldt = kmalloc(sizeof(struct ldt_struct), GFP_KERNEL);
46	if (!new_ldt)
47		return NULL;
48
49	BUILD_BUG_ON(LDT_ENTRY_SIZE != sizeof(struct desc_struct));
50	alloc_size = size * LDT_ENTRY_SIZE;
51
52	/*
53	 * Xen is very picky: it requires a page-aligned LDT that has no
54	 * trailing nonzero bytes in any page that contains LDT descriptors.
55	 * Keep it simple: zero the whole allocation and never allocate less
56	 * than PAGE_SIZE.
57	 */
58	if (alloc_size > PAGE_SIZE)
59		new_ldt->entries = vzalloc(alloc_size);
60	else
61		new_ldt->entries = (void *)get_zeroed_page(GFP_KERNEL);
62
63	if (!new_ldt->entries) {
64		kfree(new_ldt);
65		return NULL;
66	}
67
68	new_ldt->size = size;
69	return new_ldt;
70}
71
72/* After calling this, the LDT is immutable. */
73static void finalize_ldt_struct(struct ldt_struct *ldt)
74{
75	paravirt_alloc_ldt(ldt->entries, ldt->size);
76}
77
78/* context.lock is held */
79static void install_ldt(struct mm_struct *current_mm,
80			struct ldt_struct *ldt)
81{
82	/* Synchronizes with lockless_dereference in load_mm_ldt. */
83	smp_store_release(&current_mm->context.ldt, ldt);
84
85	/* Activate the LDT for all CPUs using current_mm. */
86	on_each_cpu_mask(mm_cpumask(current_mm), flush_ldt, current_mm, true);
87}
88
89static void free_ldt_struct(struct ldt_struct *ldt)
90{
91	if (likely(!ldt))
92		return;
93
94	paravirt_free_ldt(ldt->entries, ldt->size);
95	if (ldt->size * LDT_ENTRY_SIZE > PAGE_SIZE)
96		vfree(ldt->entries);
97	else
98		free_page((unsigned long)ldt->entries);
99	kfree(ldt);
100}
101
102/*
103 * we do not have to muck with descriptors here, that is
104 * done in switch_mm() as needed.
105 */
106int init_new_context(struct task_struct *tsk, struct mm_struct *mm)
107{
108	struct ldt_struct *new_ldt;
109	struct mm_struct *old_mm;
110	int retval = 0;
111
112	mutex_init(&mm->context.lock);
113	old_mm = current->mm;
114	if (!old_mm) {
115		mm->context.ldt = NULL;
116		return 0;
117	}
118
119	mutex_lock(&old_mm->context.lock);
120	if (!old_mm->context.ldt) {
121		mm->context.ldt = NULL;
122		goto out_unlock;
123	}
124
125	new_ldt = alloc_ldt_struct(old_mm->context.ldt->size);
126	if (!new_ldt) {
127		retval = -ENOMEM;
128		goto out_unlock;
129	}
130
131	memcpy(new_ldt->entries, old_mm->context.ldt->entries,
132	       new_ldt->size * LDT_ENTRY_SIZE);
133	finalize_ldt_struct(new_ldt);
134
135	mm->context.ldt = new_ldt;
136
137out_unlock:
138	mutex_unlock(&old_mm->context.lock);
139	return retval;
140}
141
142/*
143 * No need to lock the MM as we are the last user
144 *
145 * 64bit: Don't touch the LDT register - we're already in the next thread.
146 */
147void destroy_context(struct mm_struct *mm)
148{
149	free_ldt_struct(mm->context.ldt);
150	mm->context.ldt = NULL;
151}
152
153static int read_ldt(void __user *ptr, unsigned long bytecount)
154{
155	int retval;
156	unsigned long size;
157	struct mm_struct *mm = current->mm;
158
159	mutex_lock(&mm->context.lock);
160
161	if (!mm->context.ldt) {
162		retval = 0;
163		goto out_unlock;
164	}
165
166	if (bytecount > LDT_ENTRY_SIZE * LDT_ENTRIES)
167		bytecount = LDT_ENTRY_SIZE * LDT_ENTRIES;
168
169	size = mm->context.ldt->size * LDT_ENTRY_SIZE;
170	if (size > bytecount)
171		size = bytecount;
172
173	if (copy_to_user(ptr, mm->context.ldt->entries, size)) {
174		retval = -EFAULT;
175		goto out_unlock;
176	}
177
178	if (size != bytecount) {
179		/* Zero-fill the rest and pretend we read bytecount bytes. */
180		if (clear_user(ptr + size, bytecount - size)) {
181			retval = -EFAULT;
182			goto out_unlock;
183		}
184	}
185	retval = bytecount;
186
187out_unlock:
188	mutex_unlock(&mm->context.lock);
189	return retval;
190}
191
192static int read_default_ldt(void __user *ptr, unsigned long bytecount)
193{
194	/* CHECKME: Can we use _one_ random number ? */
195#ifdef CONFIG_X86_32
196	unsigned long size = 5 * sizeof(struct desc_struct);
197#else
198	unsigned long size = 128;
199#endif
200	if (bytecount > size)
201		bytecount = size;
202	if (clear_user(ptr, bytecount))
203		return -EFAULT;
204	return bytecount;
205}
206
207static int write_ldt(void __user *ptr, unsigned long bytecount, int oldmode)
208{
209	struct mm_struct *mm = current->mm;
210	struct desc_struct ldt;
211	int error;
212	struct user_desc ldt_info;
213	int oldsize, newsize;
214	struct ldt_struct *new_ldt, *old_ldt;
215
216	error = -EINVAL;
217	if (bytecount != sizeof(ldt_info))
218		goto out;
219	error = -EFAULT;
220	if (copy_from_user(&ldt_info, ptr, sizeof(ldt_info)))
221		goto out;
222
223	error = -EINVAL;
224	if (ldt_info.entry_number >= LDT_ENTRIES)
225		goto out;
226	if (ldt_info.contents == 3) {
227		if (oldmode)
228			goto out;
229		if (ldt_info.seg_not_present == 0)
230			goto out;
231	}
232
233	if ((oldmode && !ldt_info.base_addr && !ldt_info.limit) ||
234	    LDT_empty(&ldt_info)) {
235		/* The user wants to clear the entry. */
236		memset(&ldt, 0, sizeof(ldt));
237	} else {
238		if (!IS_ENABLED(CONFIG_X86_16BIT) && !ldt_info.seg_32bit) {
239			error = -EINVAL;
240			goto out;
241		}
242
243		fill_ldt(&ldt, &ldt_info);
244		if (oldmode)
245			ldt.avl = 0;
246	}
247
248	mutex_lock(&mm->context.lock);
249
250	old_ldt = mm->context.ldt;
251	oldsize = old_ldt ? old_ldt->size : 0;
252	newsize = max((int)(ldt_info.entry_number + 1), oldsize);
253
254	error = -ENOMEM;
255	new_ldt = alloc_ldt_struct(newsize);
256	if (!new_ldt)
257		goto out_unlock;
258
259	if (old_ldt)
260		memcpy(new_ldt->entries, old_ldt->entries, oldsize * LDT_ENTRY_SIZE);
261	new_ldt->entries[ldt_info.entry_number] = ldt;
262	finalize_ldt_struct(new_ldt);
263
264	install_ldt(mm, new_ldt);
265	free_ldt_struct(old_ldt);
266	error = 0;
267
268out_unlock:
269	mutex_unlock(&mm->context.lock);
270out:
271	return error;
272}
273
274asmlinkage int sys_modify_ldt(int func, void __user *ptr,
275			      unsigned long bytecount)
276{
277	int ret = -ENOSYS;
278
279	switch (func) {
280	case 0:
281		ret = read_ldt(ptr, bytecount);
282		break;
283	case 1:
284		ret = write_ldt(ptr, bytecount, 1);
285		break;
286	case 2:
287		ret = read_default_ldt(ptr, bytecount);
288		break;
289	case 0x11:
290		ret = write_ldt(ptr, bytecount, 0);
291		break;
292	}
293	return ret;
294}
295