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