arch/arm/lib/uaccess_with_memcpy.c

   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 <asm/current.h>
  20 #include <asm/page.h>
  21
  22 static int
  23 pin_page_for_write(const void __user *_addr, pte_t **ptep, spinlock_t **ptlp)
  24 {
  25         unsigned long addr = (unsigned long)_addr;
  26         pgd_t *pgd;
  27         pmd_t *pmd;
  28         pte_t *pte;
  29         spinlock_t *ptl;
  30
  31         pgd = pgd_offset(current->mm, addr);
  32         if (unlikely(pgd_none(*pgd) || pgd_bad(*pgd)))
  33                 return 0;
  34
  35         pmd = pmd_offset(pgd, addr);
  36         if (unlikely(pmd_none(*pmd) || pmd_bad(*pmd)))
  37                 return 0;
  38
  39         pte = pte_offset_map_lock(current->mm, pmd, addr, &ptl);
  40         if (unlikely(!pte_present(*pte) || !pte_young(*pte) ||
  41             !pte_write(*pte) || !pte_dirty(*pte))) {
  42                 pte_unmap_unlock(pte, ptl);
  43                 return 0;
  44         }
  45
  46         *ptep = pte;
  47         *ptlp = ptl;
  48
  49         return 1;
  50 }
  51
  52 static unsigned long noinline
  53 __copy_to_user_memcpy(void __user *to, const void *from, unsigned long n)
  54 {
  55         int atomic;
  56
  57         if (unlikely(segment_eq(get_fs(), KERNEL_DS))) {
  58                 memcpy((void *)to, from, n);
  59                 return 0;
  60         }
  61
  62         /* the mmap semaphore is taken only if not in an atomic context */
  63         atomic = in_atomic();
  64
  65         if (!atomic)
  66                 down_read(&current->mm->mmap_sem);
  67         while (n) {
  68                 pte_t *pte;
  69                 spinlock_t *ptl;
  70                 int tocopy;
  71
  72                 while (!pin_page_for_write(to, &pte, &ptl)) {
  73                         if (!atomic)
  74                                 up_read(&current->mm->mmap_sem);
  75                         if (__put_user(0, (char __user *)to))
  76                                 goto out;
  77                         if (!atomic)
  78                                 down_read(&current->mm->mmap_sem);
  79                 }
  80
  81                 tocopy = (~(unsigned long)to & ~PAGE_MASK) + 1;
  82                 if (tocopy > n)
  83                         tocopy = n;
  84
  85                 memcpy((void *)to, from, tocopy);
  86                 to += tocopy;
  87                 from += tocopy;
  88                 n -= tocopy;
  89
  90                 pte_unmap_unlock(pte, ptl);
  91         }
  92         if (!atomic)
  93                 up_read(&current->mm->mmap_sem);
  94
  95 out:
  96         return n;
  97 }
  98
  99 unsigned long
 100 __copy_to_user(void __user *to, const void *from, unsigned long n)
 101 {
 102         /*
 103          * This test is stubbed out of the main function above to keep
 104          * the overhead for small copies low by avoiding a large
 105          * register dump on the stack just to reload them right away.
 106          * With frame pointer disabled, tail call optimization kicks in
 107          * as well making this test almost invisible.
 108          */
 109         if (n < 64)
 110                 return __copy_to_user_std(to, from, n);
 111         return __copy_to_user_memcpy(to, from, n);
 112 }
 113
 114 static unsigned long noinline
 115 __clear_user_memset(void __user *addr, unsigned long n)
 116 {
 117         if (unlikely(segment_eq(get_fs(), KERNEL_DS))) {
 118                 memset((void *)addr, 0, n);
 119                 return 0;
 120         }
 121
 122         down_read(&current->mm->mmap_sem);
 123         while (n) {
 124                 pte_t *pte;
 125                 spinlock_t *ptl;
 126                 int tocopy;
 127
 128                 while (!pin_page_for_write(addr, &pte, &ptl)) {
 129                         up_read(&current->mm->mmap_sem);
 130                         if (__put_user(0, (char __user *)addr))
 131                                 goto out;
 132                         down_read(&current->mm->mmap_sem);
 133                 }
 134
 135                 tocopy = (~(unsigned long)addr & ~PAGE_MASK) + 1;
 136                 if (tocopy > n)
 137                         tocopy = n;
 138
 139                 memset((void *)addr, 0, tocopy);
 140                 addr += tocopy;
 141                 n -= tocopy;
 142
 143                 pte_unmap_unlock(pte, ptl);
 144         }
 145         up_read(&current->mm->mmap_sem);
 146
 147 out:
 148         return n;
 149 }
 150
 151 unsigned long __clear_user(void __user *addr, unsigned long n)
 152 {
 153         /* See rational for this in __copy_to_user() above. */
 154         if (n < 64)
 155                 return __clear_user_std(addr, n);
 156         return __clear_user_memset(addr, n);
 157 }
 158
 159 #if 0
 160
 161 /*
 162  * This code is disabled by default, but kept around in case the chosen
 163  * thresholds need to be revalidated.  Some overhead (small but still)
 164  * would be implied by a runtime determined variable threshold, and
 165  * so far the measurement on concerned targets didn't show a worthwhile
 166  * variation.
 167  *
 168  * Note that a fairly precise sched_clock() implementation is needed
 169  * for results to make some sense.
 170  */
 171
 172 #include <linux/vmalloc.h>
 173
 174 static int __init test_size_treshold(void)
 175 {
 176         struct page *src_page, *dst_page;
 177         void *user_ptr, *kernel_ptr;
 178         unsigned long long t0, t1, t2;
 179         int size, ret;
 180
 181         ret = -ENOMEM;
 182         src_page = alloc_page(GFP_KERNEL);
 183         if (!src_page)
 184                 goto no_src;
 185         dst_page = alloc_page(GFP_KERNEL);
 186         if (!dst_page)
 187                 goto no_dst;
 188         kernel_ptr = page_address(src_page);
 189         user_ptr = vmap(&dst_page, 1, VM_IOREMAP, __pgprot(__P010));
 190         if (!user_ptr)
 191                 goto no_vmap;
 192
 193         /* warm up the src page dcache */
 194         ret = __copy_to_user_memcpy(user_ptr, kernel_ptr, PAGE_SIZE);
 195
 196         for (size = PAGE_SIZE; size >= 4; size /= 2) {
 197                 t0 = sched_clock();
 198                 ret |= __copy_to_user_memcpy(user_ptr, kernel_ptr, size);
 199                 t1 = sched_clock();
 200                 ret |= __copy_to_user_std(user_ptr, kernel_ptr, size);
 201                 t2 = sched_clock();
 202                 printk("copy_to_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
 203         }
 204
 205         for (size = PAGE_SIZE; size >= 4; size /= 2) {
 206                 t0 = sched_clock();
 207                 ret |= __clear_user_memset(user_ptr, size);
 208                 t1 = sched_clock();
 209                 ret |= __clear_user_std(user_ptr, size);
 210                 t2 = sched_clock();
 211                 printk("clear_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
 212         }
 213
 214         if (ret)
 215                 ret = -EFAULT;
 216
 217         vunmap(user_ptr);
 218 no_vmap:
 219         put_page(dst_page);
 220 no_dst:
 221         put_page(src_page);
 222 no_src:
 223         return ret;
 224 }
 225
 226 subsys_initcall(test_size_treshold);
 227
 228 #endif