arch/arm/lib/uaccess_with_memcpy.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  *  linux/arch/arm/lib/uaccess_with_memcpy.c
   4  *
   5  *  Written by: Lennert Buytenhek and Nicolas Pitre
   6  *  Copyright (C) 2009 Marvell Semiconductor
   7  */
   8
   9 #include <linux/kernel.h>
  10 #include <linux/ctype.h>
  11 #include <linux/uaccess.h>
  12 #include <linux/rwsem.h>
  13 #include <linux/mm.h>
  14 #include <linux/sched.h>
  15 #include <linux/hardirq.h> /* for in_atomic() */
  16 #include <linux/gfp.h>
  17 #include <linux/highmem.h>
  18 #include <linux/hugetlb.h>
  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         p4d_t *p4d;
  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         p4d = p4d_offset(pgd, addr);
  38         if (unlikely(p4d_none(*p4d) || p4d_bad(*p4d)))
  39                 return 0;
  40
  41         pud = pud_offset(p4d, addr);
  42         if (unlikely(pud_none(*pud) || pud_bad(*pud)))
  43                 return 0;
  44
  45         pmd = pmd_offset(pud, addr);
  46         if (unlikely(pmd_none(*pmd)))
  47                 return 0;
  48
  49         /*
  50          * A pmd can be bad if it refers to a HugeTLB or THP page.
  51          *
  52          * Both THP and HugeTLB pages have the same pmd layout
  53          * and should not be manipulated by the pte functions.
  54          *
  55          * Lock the page table for the destination and check
  56          * to see that it's still huge and whether or not we will
  57          * need to fault on write.
  58          */
  59         if (unlikely(pmd_thp_or_huge(*pmd))) {
  60                 ptl = &current->mm->page_table_lock;
  61                 spin_lock(ptl);
  62                 if (unlikely(!pmd_thp_or_huge(*pmd)
  63                         || pmd_hugewillfault(*pmd))) {
  64                         spin_unlock(ptl);
  65                         return 0;
  66                 }
  67
  68                 *ptep = NULL;
  69                 *ptlp = ptl;
  70                 return 1;
  71         }
  72
  73         if (unlikely(pmd_bad(*pmd)))
  74                 return 0;
  75
  76         pte = pte_offset_map_lock(current->mm, pmd, addr, &ptl);
  77         if (unlikely(!pte_present(*pte) || !pte_young(*pte) ||
  78             !pte_write(*pte) || !pte_dirty(*pte))) {
  79                 pte_unmap_unlock(pte, ptl);
  80                 return 0;
  81         }
  82
  83         *ptep = pte;
  84         *ptlp = ptl;
  85
  86         return 1;
  87 }
  88
  89 static unsigned long noinline
  90 __copy_to_user_memcpy(void __user *to, const void *from, unsigned long n)
  91 {
  92         unsigned long ua_flags;
  93         int atomic;
  94
  95         /* the mmap semaphore is taken only if not in an atomic context */
  96         atomic = faulthandler_disabled();
  97
  98         if (!atomic)
  99                 mmap_read_lock(current->mm);
 100         while (n) {
 101                 pte_t *pte;
 102                 spinlock_t *ptl;
 103                 int tocopy;
 104
 105                 while (!pin_page_for_write(to, &pte, &ptl)) {
 106                         if (!atomic)
 107                                 mmap_read_unlock(current->mm);
 108                         if (__put_user(0, (char __user *)to))
 109                                 goto out;
 110                         if (!atomic)
 111                                 mmap_read_lock(current->mm);
 112                 }
 113
 114                 tocopy = (~(unsigned long)to & ~PAGE_MASK) + 1;
 115                 if (tocopy > n)
 116                         tocopy = n;
 117
 118                 ua_flags = uaccess_save_and_enable();
 119                 memcpy((void *)to, from, tocopy);
 120                 uaccess_restore(ua_flags);
 121                 to += tocopy;
 122                 from += tocopy;
 123                 n -= tocopy;
 124
 125                 if (pte)
 126                         pte_unmap_unlock(pte, ptl);
 127                 else
 128                         spin_unlock(ptl);
 129         }
 130         if (!atomic)
 131                 mmap_read_unlock(current->mm);
 132
 133 out:
 134         return n;
 135 }
 136
 137 unsigned long
 138 arm_copy_to_user(void __user *to, const void *from, unsigned long n)
 139 {
 140         /*
 141          * This test is stubbed out of the main function above to keep
 142          * the overhead for small copies low by avoiding a large
 143          * register dump on the stack just to reload them right away.
 144          * With frame pointer disabled, tail call optimization kicks in
 145          * as well making this test almost invisible.
 146          */
 147         if (n < 64) {
 148                 unsigned long ua_flags = uaccess_save_and_enable();
 149                 n = __copy_to_user_std(to, from, n);
 150                 uaccess_restore(ua_flags);
 151         } else {
 152                 n = __copy_to_user_memcpy(uaccess_mask_range_ptr(to, n),
 153                                           from, n);
 154         }
 155         return n;
 156 }
 157
 158 static unsigned long noinline
 159 __clear_user_memset(void __user *addr, unsigned long n)
 160 {
 161         unsigned long ua_flags;
 162
 163         mmap_read_lock(current->mm);
 164         while (n) {
 165                 pte_t *pte;
 166                 spinlock_t *ptl;
 167                 int tocopy;
 168
 169                 while (!pin_page_for_write(addr, &pte, &ptl)) {
 170                         mmap_read_unlock(current->mm);
 171                         if (__put_user(0, (char __user *)addr))
 172                                 goto out;
 173                         mmap_read_lock(current->mm);
 174                 }
 175
 176                 tocopy = (~(unsigned long)addr & ~PAGE_MASK) + 1;
 177                 if (tocopy > n)
 178                         tocopy = n;
 179
 180                 ua_flags = uaccess_save_and_enable();
 181                 memset((void *)addr, 0, tocopy);
 182                 uaccess_restore(ua_flags);
 183                 addr += tocopy;
 184                 n -= tocopy;
 185
 186                 if (pte)
 187                         pte_unmap_unlock(pte, ptl);
 188                 else
 189                         spin_unlock(ptl);
 190         }
 191         mmap_read_unlock(current->mm);
 192
 193 out:
 194         return n;
 195 }
 196
 197 unsigned long arm_clear_user(void __user *addr, unsigned long n)
 198 {
 199         /* See rational for this in __copy_to_user() above. */
 200         if (n < 64) {
 201                 unsigned long ua_flags = uaccess_save_and_enable();
 202                 n = __clear_user_std(addr, n);
 203                 uaccess_restore(ua_flags);
 204         } else {
 205                 n = __clear_user_memset(addr, n);
 206         }
 207         return n;
 208 }
 209
 210 #if 0
 211
 212 /*
 213  * This code is disabled by default, but kept around in case the chosen
 214  * thresholds need to be revalidated.  Some overhead (small but still)
 215  * would be implied by a runtime determined variable threshold, and
 216  * so far the measurement on concerned targets didn't show a worthwhile
 217  * variation.
 218  *
 219  * Note that a fairly precise sched_clock() implementation is needed
 220  * for results to make some sense.
 221  */
 222
 223 #include <linux/vmalloc.h>
 224
 225 static int __init test_size_treshold(void)
 226 {
 227         struct page *src_page, *dst_page;
 228         void *user_ptr, *kernel_ptr;
 229         unsigned long long t0, t1, t2;
 230         int size, ret;
 231
 232         ret = -ENOMEM;
 233         src_page = alloc_page(GFP_KERNEL);
 234         if (!src_page)
 235                 goto no_src;
 236         dst_page = alloc_page(GFP_KERNEL);
 237         if (!dst_page)
 238                 goto no_dst;
 239         kernel_ptr = page_address(src_page);
 240         user_ptr = vmap(&dst_page, 1, VM_IOREMAP, __pgprot(__PAGE_COPY));
 241         if (!user_ptr)
 242                 goto no_vmap;
 243
 244         /* warm up the src page dcache */
 245         ret = __copy_to_user_memcpy(user_ptr, kernel_ptr, PAGE_SIZE);
 246
 247         for (size = PAGE_SIZE; size >= 4; size /= 2) {
 248                 t0 = sched_clock();
 249                 ret |= __copy_to_user_memcpy(user_ptr, kernel_ptr, size);
 250                 t1 = sched_clock();
 251                 ret |= __copy_to_user_std(user_ptr, kernel_ptr, size);
 252                 t2 = sched_clock();
 253                 printk("copy_to_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
 254         }
 255
 256         for (size = PAGE_SIZE; size >= 4; size /= 2) {
 257                 t0 = sched_clock();
 258                 ret |= __clear_user_memset(user_ptr, size);
 259                 t1 = sched_clock();
 260                 ret |= __clear_user_std(user_ptr, size);
 261                 t2 = sched_clock();
 262                 printk("clear_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
 263         }
 264
 265         if (ret)
 266                 ret = -EFAULT;
 267
 268         vunmap(user_ptr);
 269 no_vmap:
 270         put_page(dst_page);
 271 no_dst:
 272         put_page(src_page);
 273 no_src:
 274         return ret;
 275 }
 276
 277 subsys_initcall(test_size_treshold);
 278
 279 #endif