Linux Kernel  3.7.1
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uaccess_with_memcpy.c
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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 
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