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 <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
  64         if (unlikely(segment_eq(get_fs(), KERNEL_DS))) {
  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