1/*
2 *  linux/arch/arm/lib/uaccess_with_memcpy.c
3 *
4 *  Written by: Lennert Buytenhek and Nicolas Pitre
5 *  Copyright (C) 2009 Marvell Semiconductor
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License version 2 as
9 * published by the Free Software Foundation.
10 */
11
12#include <linux/kernel.h>
13#include <linux/ctype.h>
14#include <linux/uaccess.h>
15#include <linux/rwsem.h>
16#include <linux/mm.h>
17#include <linux/sched.h>
18#include <linux/hardirq.h> /* for in_atomic() */
19#include <linux/gfp.h>
20#include <linux/highmem.h>
21#include <linux/hugetlb.h>
22#include <asm/current.h>
23#include <asm/page.h>
24
25static int
26pin_page_for_write(const void __user *_addr, pte_t **ptep, spinlock_t **ptlp)
27{
28	unsigned long addr = (unsigned long)_addr;
29	pgd_t *pgd;
30	pmd_t *pmd;
31	pte_t *pte;
32	pud_t *pud;
33	spinlock_t *ptl;
34
35	pgd = pgd_offset(current->mm, addr);
36	if (unlikely(pgd_none(*pgd) || pgd_bad(*pgd)))
37		return 0;
38
39	pud = pud_offset(pgd, addr);
40	if (unlikely(pud_none(*pud) || pud_bad(*pud)))
41		return 0;
42
43	pmd = pmd_offset(pud, addr);
44	if (unlikely(pmd_none(*pmd)))
45		return 0;
46
47	/*
48	 * A pmd can be bad if it refers to a HugeTLB or THP page.
49	 *
50	 * Both THP and HugeTLB pages have the same pmd layout
51	 * and should not be manipulated by the pte functions.
52	 *
53	 * Lock the page table for the destination and check
54	 * to see that it's still huge and whether or not we will
55	 * need to fault on write, or if we have a splitting THP.
56	 */
57	if (unlikely(pmd_thp_or_huge(*pmd))) {
58		ptl = &current->mm->page_table_lock;
59		spin_lock(ptl);
60		if (unlikely(!pmd_thp_or_huge(*pmd)
61			|| pmd_hugewillfault(*pmd)
62			|| pmd_trans_splitting(*pmd))) {
63			spin_unlock(ptl);
64			return 0;
65		}
66
67		*ptep = NULL;
68		*ptlp = ptl;
69		return 1;
70	}
71
72	if (unlikely(pmd_bad(*pmd)))
73		return 0;
74
75	pte = pte_offset_map_lock(current->mm, pmd, addr, &ptl);
76	if (unlikely(!pte_present(*pte) || !pte_young(*pte) ||
77	    !pte_write(*pte) || !pte_dirty(*pte))) {
78		pte_unmap_unlock(pte, ptl);
79		return 0;
80	}
81
82	*ptep = pte;
83	*ptlp = ptl;
84
85	return 1;
86}
87
88static unsigned long noinline
89__copy_to_user_memcpy(void __user *to, const void *from, unsigned long n)
90{
91	int atomic;
92
93	if (unlikely(segment_eq(get_fs(), KERNEL_DS))) {
94		memcpy((void *)to, from, n);
95		return 0;
96	}
97
98	/* the mmap semaphore is taken only if not in an atomic context */
99	atomic = in_atomic();
100
101	if (!atomic)
102		down_read(&current->mm->mmap_sem);
103	while (n) {
104		pte_t *pte;
105		spinlock_t *ptl;
106		int tocopy;
107
108		while (!pin_page_for_write(to, &pte, &ptl)) {
109			if (!atomic)
110				up_read(&current->mm->mmap_sem);
111			if (__put_user(0, (char __user *)to))
112				goto out;
113			if (!atomic)
114				down_read(&current->mm->mmap_sem);
115		}
116
117		tocopy = (~(unsigned long)to & ~PAGE_MASK) + 1;
118		if (tocopy > n)
119			tocopy = n;
120
121		memcpy((void *)to, from, tocopy);
122		to += tocopy;
123		from += tocopy;
124		n -= tocopy;
125
126		if (pte)
127			pte_unmap_unlock(pte, ptl);
128		else
129			spin_unlock(ptl);
130	}
131	if (!atomic)
132		up_read(&current->mm->mmap_sem);
133
134out:
135	return n;
136}
137
138unsigned long
139__copy_to_user(void __user *to, const void *from, unsigned long n)
140{
141	/*
142	 * This test is stubbed out of the main function above to keep
143	 * the overhead for small copies low by avoiding a large
144	 * register dump on the stack just to reload them right away.
145	 * With frame pointer disabled, tail call optimization kicks in
146	 * as well making this test almost invisible.
147	 */
148	if (n < 64)
149		return __copy_to_user_std(to, from, n);
150	return __copy_to_user_memcpy(to, from, n);
151}
152
153static unsigned long noinline
154__clear_user_memset(void __user *addr, unsigned long n)
155{
156	if (unlikely(segment_eq(get_fs(), KERNEL_DS))) {
157		memset((void *)addr, 0, n);
158		return 0;
159	}
160
161	down_read(&current->mm->mmap_sem);
162	while (n) {
163		pte_t *pte;
164		spinlock_t *ptl;
165		int tocopy;
166
167		while (!pin_page_for_write(addr, &pte, &ptl)) {
168			up_read(&current->mm->mmap_sem);
169			if (__put_user(0, (char __user *)addr))
170				goto out;
171			down_read(&current->mm->mmap_sem);
172		}
173
174		tocopy = (~(unsigned long)addr & ~PAGE_MASK) + 1;
175		if (tocopy > n)
176			tocopy = n;
177
178		memset((void *)addr, 0, tocopy);
179		addr += tocopy;
180		n -= tocopy;
181
182		if (pte)
183			pte_unmap_unlock(pte, ptl);
184		else
185			spin_unlock(ptl);
186	}
187	up_read(&current->mm->mmap_sem);
188
189out:
190	return n;
191}
192
193unsigned long __clear_user(void __user *addr, unsigned long n)
194{
195	/* See rational for this in __copy_to_user() above. */
196	if (n < 64)
197		return __clear_user_std(addr, n);
198	return __clear_user_memset(addr, n);
199}
200
201#if 0
202
203/*
204 * This code is disabled by default, but kept around in case the chosen
205 * thresholds need to be revalidated.  Some overhead (small but still)
206 * would be implied by a runtime determined variable threshold, and
207 * so far the measurement on concerned targets didn't show a worthwhile
208 * variation.
209 *
210 * Note that a fairly precise sched_clock() implementation is needed
211 * for results to make some sense.
212 */
213
214#include <linux/vmalloc.h>
215
216static int __init test_size_treshold(void)
217{
218	struct page *src_page, *dst_page;
219	void *user_ptr, *kernel_ptr;
220	unsigned long long t0, t1, t2;
221	int size, ret;
222
223	ret = -ENOMEM;
224	src_page = alloc_page(GFP_KERNEL);
225	if (!src_page)
226		goto no_src;
227	dst_page = alloc_page(GFP_KERNEL);
228	if (!dst_page)
229		goto no_dst;
230	kernel_ptr = page_address(src_page);
231	user_ptr = vmap(&dst_page, 1, VM_IOREMAP, __pgprot(__P010));
232	if (!user_ptr)
233		goto no_vmap;
234
235	/* warm up the src page dcache */
236	ret = __copy_to_user_memcpy(user_ptr, kernel_ptr, PAGE_SIZE);
237
238	for (size = PAGE_SIZE; size >= 4; size /= 2) {
239		t0 = sched_clock();
240		ret |= __copy_to_user_memcpy(user_ptr, kernel_ptr, size);
241		t1 = sched_clock();
242		ret |= __copy_to_user_std(user_ptr, kernel_ptr, size);
243		t2 = sched_clock();
244		printk("copy_to_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
245	}
246
247	for (size = PAGE_SIZE; size >= 4; size /= 2) {
248		t0 = sched_clock();
249		ret |= __clear_user_memset(user_ptr, size);
250		t1 = sched_clock();
251		ret |= __clear_user_std(user_ptr, size);
252		t2 = sched_clock();
253		printk("clear_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
254	}
255
256	if (ret)
257		ret = -EFAULT;
258
259	vunmap(user_ptr);
260no_vmap:
261	put_page(dst_page);
262no_dst:
263	put_page(src_page);
264no_src:
265	return ret;
266}
267
268subsys_initcall(test_size_treshold);
269
270#endif
271