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