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
25 static int
pin_page_for_write(const void __user * _addr,pte_t ** ptep,spinlock_t ** ptlp)26 pin_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 = ¤t->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
88 static unsigned long noinline
__copy_to_user_memcpy(void __user * to,const void * from,unsigned long n)89 __copy_to_user_memcpy(void __user *to, const void *from, unsigned long n)
90 {
91 unsigned long ua_flags;
92 int atomic;
93
94 if (unlikely(segment_eq(get_fs(), KERNEL_DS))) {
95 memcpy((void *)to, from, n);
96 return 0;
97 }
98
99 /* the mmap semaphore is taken only if not in an atomic context */
100 atomic = faulthandler_disabled();
101
102 if (!atomic)
103 down_read(¤t->mm->mmap_sem);
104 while (n) {
105 pte_t *pte;
106 spinlock_t *ptl;
107 int tocopy;
108
109 while (!pin_page_for_write(to, &pte, &ptl)) {
110 if (!atomic)
111 up_read(¤t->mm->mmap_sem);
112 if (__put_user(0, (char __user *)to))
113 goto out;
114 if (!atomic)
115 down_read(¤t->mm->mmap_sem);
116 }
117
118 tocopy = (~(unsigned long)to & ~PAGE_MASK) + 1;
119 if (tocopy > n)
120 tocopy = n;
121
122 ua_flags = uaccess_save_and_enable();
123 memcpy((void *)to, from, tocopy);
124 uaccess_restore(ua_flags);
125 to += tocopy;
126 from += tocopy;
127 n -= tocopy;
128
129 if (pte)
130 pte_unmap_unlock(pte, ptl);
131 else
132 spin_unlock(ptl);
133 }
134 if (!atomic)
135 up_read(¤t->mm->mmap_sem);
136
137 out:
138 return n;
139 }
140
141 unsigned long
arm_copy_to_user(void __user * to,const void * from,unsigned long n)142 arm_copy_to_user(void __user *to, const void *from, unsigned long n)
143 {
144 /*
145 * This test is stubbed out of the main function above to keep
146 * the overhead for small copies low by avoiding a large
147 * register dump on the stack just to reload them right away.
148 * With frame pointer disabled, tail call optimization kicks in
149 * as well making this test almost invisible.
150 */
151 if (n < 64) {
152 unsigned long ua_flags = uaccess_save_and_enable();
153 n = __copy_to_user_std(to, from, n);
154 uaccess_restore(ua_flags);
155 } else {
156 n = __copy_to_user_memcpy(to, from, n);
157 }
158 return n;
159 }
160
161 static unsigned long noinline
__clear_user_memset(void __user * addr,unsigned long n)162 __clear_user_memset(void __user *addr, unsigned long n)
163 {
164 unsigned long ua_flags;
165
166 if (unlikely(segment_eq(get_fs(), KERNEL_DS))) {
167 memset((void *)addr, 0, n);
168 return 0;
169 }
170
171 down_read(¤t->mm->mmap_sem);
172 while (n) {
173 pte_t *pte;
174 spinlock_t *ptl;
175 int tocopy;
176
177 while (!pin_page_for_write(addr, &pte, &ptl)) {
178 up_read(¤t->mm->mmap_sem);
179 if (__put_user(0, (char __user *)addr))
180 goto out;
181 down_read(¤t->mm->mmap_sem);
182 }
183
184 tocopy = (~(unsigned long)addr & ~PAGE_MASK) + 1;
185 if (tocopy > n)
186 tocopy = n;
187
188 ua_flags = uaccess_save_and_enable();
189 memset((void *)addr, 0, tocopy);
190 uaccess_restore(ua_flags);
191 addr += tocopy;
192 n -= tocopy;
193
194 if (pte)
195 pte_unmap_unlock(pte, ptl);
196 else
197 spin_unlock(ptl);
198 }
199 up_read(¤t->mm->mmap_sem);
200
201 out:
202 return n;
203 }
204
arm_clear_user(void __user * addr,unsigned long n)205 unsigned long arm_clear_user(void __user *addr, unsigned long n)
206 {
207 /* See rational for this in __copy_to_user() above. */
208 if (n < 64) {
209 unsigned long ua_flags = uaccess_save_and_enable();
210 n = __clear_user_std(addr, n);
211 uaccess_restore(ua_flags);
212 } else {
213 n = __clear_user_memset(addr, n);
214 }
215 return n;
216 }
217
218 #if 0
219
220 /*
221 * This code is disabled by default, but kept around in case the chosen
222 * thresholds need to be revalidated. Some overhead (small but still)
223 * would be implied by a runtime determined variable threshold, and
224 * so far the measurement on concerned targets didn't show a worthwhile
225 * variation.
226 *
227 * Note that a fairly precise sched_clock() implementation is needed
228 * for results to make some sense.
229 */
230
231 #include <linux/vmalloc.h>
232
233 static int __init test_size_treshold(void)
234 {
235 struct page *src_page, *dst_page;
236 void *user_ptr, *kernel_ptr;
237 unsigned long long t0, t1, t2;
238 int size, ret;
239
240 ret = -ENOMEM;
241 src_page = alloc_page(GFP_KERNEL);
242 if (!src_page)
243 goto no_src;
244 dst_page = alloc_page(GFP_KERNEL);
245 if (!dst_page)
246 goto no_dst;
247 kernel_ptr = page_address(src_page);
248 user_ptr = vmap(&dst_page, 1, VM_IOREMAP, __pgprot(__P010));
249 if (!user_ptr)
250 goto no_vmap;
251
252 /* warm up the src page dcache */
253 ret = __copy_to_user_memcpy(user_ptr, kernel_ptr, PAGE_SIZE);
254
255 for (size = PAGE_SIZE; size >= 4; size /= 2) {
256 t0 = sched_clock();
257 ret |= __copy_to_user_memcpy(user_ptr, kernel_ptr, size);
258 t1 = sched_clock();
259 ret |= __copy_to_user_std(user_ptr, kernel_ptr, size);
260 t2 = sched_clock();
261 printk("copy_to_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
262 }
263
264 for (size = PAGE_SIZE; size >= 4; size /= 2) {
265 t0 = sched_clock();
266 ret |= __clear_user_memset(user_ptr, size);
267 t1 = sched_clock();
268 ret |= __clear_user_std(user_ptr, size);
269 t2 = sched_clock();
270 printk("clear_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
271 }
272
273 if (ret)
274 ret = -EFAULT;
275
276 vunmap(user_ptr);
277 no_vmap:
278 put_page(dst_page);
279 no_dst:
280 put_page(src_page);
281 no_src:
282 return ret;
283 }
284
285 subsys_initcall(test_size_treshold);
286
287 #endif
288