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 <asm/current.h>
22 #include <asm/page.h>
23 
24 static int
25 pin_page_for_write(const void __user *_addr, pte_t **ptep, spinlock_t **ptlp)
26 {
27 	unsigned long addr = (unsigned long)_addr;
28 	pgd_t *pgd;
29 	pmd_t *pmd;
30 	pte_t *pte;
31 	pud_t *pud;
32 	spinlock_t *ptl;
33 
34 	pgd = pgd_offset(current->mm, addr);
35 	if (unlikely(pgd_none(*pgd) || pgd_bad(*pgd)))
36 		return 0;
37 
38 	pud = pud_offset(pgd, addr);
39 	if (unlikely(pud_none(*pud) || pud_bad(*pud)))
40 		return 0;
41 
42 	pmd = pmd_offset(pud, addr);
43 	if (unlikely(pmd_none(*pmd) || pmd_bad(*pmd)))
44 		return 0;
45 
46 	pte = pte_offset_map_lock(current->mm, pmd, addr, &ptl);
47 	if (unlikely(!pte_present(*pte) || !pte_young(*pte) ||
48 	    !pte_write(*pte) || !pte_dirty(*pte))) {
49 		pte_unmap_unlock(pte, ptl);
50 		return 0;
51 	}
52 
53 	*ptep = pte;
54 	*ptlp = ptl;
55 
56 	return 1;
57 }
58 
59 static unsigned long noinline
60 __copy_to_user_memcpy(void __user *to, const void *from, unsigned long n)
61 {
62 	int atomic;
63 
64 	if (unlikely(segment_eq(get_fs(), KERNEL_DS))) {
65 		memcpy((void *)to, from, n);
66 		return 0;
67 	}
68 
69 	/* the mmap semaphore is taken only if not in an atomic context */
70 	atomic = in_atomic();
71 
72 	if (!atomic)
73 		down_read(&current->mm->mmap_sem);
74 	while (n) {
75 		pte_t *pte;
76 		spinlock_t *ptl;
77 		int tocopy;
78 
79 		while (!pin_page_for_write(to, &pte, &ptl)) {
80 			if (!atomic)
81 				up_read(&current->mm->mmap_sem);
82 			if (__put_user(0, (char __user *)to))
83 				goto out;
84 			if (!atomic)
85 				down_read(&current->mm->mmap_sem);
86 		}
87 
88 		tocopy = (~(unsigned long)to & ~PAGE_MASK) + 1;
89 		if (tocopy > n)
90 			tocopy = n;
91 
92 		memcpy((void *)to, from, tocopy);
93 		to += tocopy;
94 		from += tocopy;
95 		n -= tocopy;
96 
97 		pte_unmap_unlock(pte, ptl);
98 	}
99 	if (!atomic)
100 		up_read(&current->mm->mmap_sem);
101 
102 out:
103 	return n;
104 }
105 
106 unsigned long
107 __copy_to_user(void __user *to, const void *from, unsigned long n)
108 {
109 	/*
110 	 * This test is stubbed out of the main function above to keep
111 	 * the overhead for small copies low by avoiding a large
112 	 * register dump on the stack just to reload them right away.
113 	 * With frame pointer disabled, tail call optimization kicks in
114 	 * as well making this test almost invisible.
115 	 */
116 	if (n < 64)
117 		return __copy_to_user_std(to, from, n);
118 	return __copy_to_user_memcpy(to, from, n);
119 }
120 
121 static unsigned long noinline
122 __clear_user_memset(void __user *addr, unsigned long n)
123 {
124 	if (unlikely(segment_eq(get_fs(), KERNEL_DS))) {
125 		memset((void *)addr, 0, n);
126 		return 0;
127 	}
128 
129 	down_read(&current->mm->mmap_sem);
130 	while (n) {
131 		pte_t *pte;
132 		spinlock_t *ptl;
133 		int tocopy;
134 
135 		while (!pin_page_for_write(addr, &pte, &ptl)) {
136 			up_read(&current->mm->mmap_sem);
137 			if (__put_user(0, (char __user *)addr))
138 				goto out;
139 			down_read(&current->mm->mmap_sem);
140 		}
141 
142 		tocopy = (~(unsigned long)addr & ~PAGE_MASK) + 1;
143 		if (tocopy > n)
144 			tocopy = n;
145 
146 		memset((void *)addr, 0, tocopy);
147 		addr += tocopy;
148 		n -= tocopy;
149 
150 		pte_unmap_unlock(pte, ptl);
151 	}
152 	up_read(&current->mm->mmap_sem);
153 
154 out:
155 	return n;
156 }
157 
158 unsigned long __clear_user(void __user *addr, unsigned long n)
159 {
160 	/* See rational for this in __copy_to_user() above. */
161 	if (n < 64)
162 		return __clear_user_std(addr, n);
163 	return __clear_user_memset(addr, n);
164 }
165 
166 #if 0
167 
168 /*
169  * This code is disabled by default, but kept around in case the chosen
170  * thresholds need to be revalidated.  Some overhead (small but still)
171  * would be implied by a runtime determined variable threshold, and
172  * so far the measurement on concerned targets didn't show a worthwhile
173  * variation.
174  *
175  * Note that a fairly precise sched_clock() implementation is needed
176  * for results to make some sense.
177  */
178 
179 #include <linux/vmalloc.h>
180 
181 static int __init test_size_treshold(void)
182 {
183 	struct page *src_page, *dst_page;
184 	void *user_ptr, *kernel_ptr;
185 	unsigned long long t0, t1, t2;
186 	int size, ret;
187 
188 	ret = -ENOMEM;
189 	src_page = alloc_page(GFP_KERNEL);
190 	if (!src_page)
191 		goto no_src;
192 	dst_page = alloc_page(GFP_KERNEL);
193 	if (!dst_page)
194 		goto no_dst;
195 	kernel_ptr = page_address(src_page);
196 	user_ptr = vmap(&dst_page, 1, VM_IOREMAP, __pgprot(__P010));
197 	if (!user_ptr)
198 		goto no_vmap;
199 
200 	/* warm up the src page dcache */
201 	ret = __copy_to_user_memcpy(user_ptr, kernel_ptr, PAGE_SIZE);
202 
203 	for (size = PAGE_SIZE; size >= 4; size /= 2) {
204 		t0 = sched_clock();
205 		ret |= __copy_to_user_memcpy(user_ptr, kernel_ptr, size);
206 		t1 = sched_clock();
207 		ret |= __copy_to_user_std(user_ptr, kernel_ptr, size);
208 		t2 = sched_clock();
209 		printk("copy_to_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
210 	}
211 
212 	for (size = PAGE_SIZE; size >= 4; size /= 2) {
213 		t0 = sched_clock();
214 		ret |= __clear_user_memset(user_ptr, size);
215 		t1 = sched_clock();
216 		ret |= __clear_user_std(user_ptr, size);
217 		t2 = sched_clock();
218 		printk("clear_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
219 	}
220 
221 	if (ret)
222 		ret = -EFAULT;
223 
224 	vunmap(user_ptr);
225 no_vmap:
226 	put_page(dst_page);
227 no_dst:
228 	put_page(src_page);
229 no_src:
230 	return ret;
231 }
232 
233 subsys_initcall(test_size_treshold);
234 
235 #endif
236