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         if (uaccess_kernel()) {
  96                 memcpy((void *)to, from, n);
  97                 return 0;
  98         }
  99
 100         /* the mmap semaphore is taken only if not in an atomic context */
 101         atomic = faulthandler_disabled();
 102
 103         if (!atomic)
 104                 mmap_read_lock(current->mm);
 105         while (n) {
 106                 pte_t *pte;
 107                 spinlock_t *ptl;
 108                 int tocopy;
 109
 110                 while (!pin_page_for_write(to, &pte, &ptl)) {
 111                         if (!atomic)
 112                                 mmap_read_unlock(current->mm);
 113                         if (__put_user(0, (char __user *)to))
 114                                 goto out;
 115                         if (!atomic)
 116                                 mmap_read_lock(current->mm);
 117                 }
 118
 119                 tocopy = (~(unsigned long)to & ~PAGE_MASK) + 1;
 120                 if (tocopy > n)
 121                         tocopy = n;
 122
 123                 ua_flags = uaccess_save_and_enable();
 124                 memcpy((void *)to, from, tocopy);
 125                 uaccess_restore(ua_flags);
 126                 to += tocopy;
 127                 from += tocopy;
 128                 n -= tocopy;
 129
 130                 if (pte)
 131                         pte_unmap_unlock(pte, ptl);
 132                 else
 133                         spin_unlock(ptl);
 134         }
 135         if (!atomic)
 136                 mmap_read_unlock(current->mm);
 137
 138 out:
 139         return n;
 140 }
 141
 142 unsigned long
 143 arm_copy_to_user(void __user *to, const void *from, unsigned long n)
 144 {
 145         /*
 146          * This test is stubbed out of the main function above to keep
 147          * the overhead for small copies low by avoiding a large
 148          * register dump on the stack just to reload them right away.
 149          * With frame pointer disabled, tail call optimization kicks in
 150          * as well making this test almost invisible.
 151          */
 152         if (n < 64) {
 153                 unsigned long ua_flags = uaccess_save_and_enable();
 154                 n = __copy_to_user_std(to, from, n);
 155                 uaccess_restore(ua_flags);
 156         } else {
 157                 n = __copy_to_user_memcpy(uaccess_mask_range_ptr(to, n),
 158                                           from, n);
 159         }
 160         return n;
 161 }
 162
 163 static unsigned long noinline
 164 __clear_user_memset(void __user *addr, unsigned long n)
 165 {
 166         unsigned long ua_flags;
 167
 168         if (uaccess_kernel()) {
 169                 memset((void *)addr, 0, n);
 170                 return 0;
 171         }
 172
 173         mmap_read_lock(current->mm);
 174         while (n) {
 175                 pte_t *pte;
 176                 spinlock_t *ptl;
 177                 int tocopy;
 178
 179                 while (!pin_page_for_write(addr, &pte, &ptl)) {
 180                         mmap_read_unlock(current->mm);
 181                         if (__put_user(0, (char __user *)addr))
 182                                 goto out;
 183                         mmap_read_lock(current->mm);
 184                 }
 185
 186                 tocopy = (~(unsigned long)addr & ~PAGE_MASK) + 1;
 187                 if (tocopy > n)
 188                         tocopy = n;
 189
 190                 ua_flags = uaccess_save_and_enable();
 191                 memset((void *)addr, 0, tocopy);
 192                 uaccess_restore(ua_flags);
 193                 addr += tocopy;
 194                 n -= tocopy;
 195
 196                 if (pte)
 197                         pte_unmap_unlock(pte, ptl);
 198                 else
 199                         spin_unlock(ptl);
 200         }
 201         mmap_read_unlock(current->mm);
 202
 203 out:
 204         return n;
 205 }
 206
 207 unsigned long arm_clear_user(void __user *addr, unsigned long n)
 208 {
 209         /* See rational for this in __copy_to_user() above. */
 210         if (n < 64) {
 211                 unsigned long ua_flags = uaccess_save_and_enable();
 212                 n = __clear_user_std(addr, n);
 213                 uaccess_restore(ua_flags);
 214         } else {
 215                 n = __clear_user_memset(addr, n);
 216         }
 217         return n;
 218 }
 219
 220 #if 0
 221
 222 /*
 223  * This code is disabled by default, but kept around in case the chosen
 224  * thresholds need to be revalidated.  Some overhead (small but still)
 225  * would be implied by a runtime determined variable threshold, and
 226  * so far the measurement on concerned targets didn't show a worthwhile
 227  * variation.
 228  *
 229  * Note that a fairly precise sched_clock() implementation is needed
 230  * for results to make some sense.
 231  */
 232
 233 #include <linux/vmalloc.h>
 234
 235 static int __init test_size_treshold(void)
 236 {
 237         struct page *src_page, *dst_page;
 238         void *user_ptr, *kernel_ptr;
 239         unsigned long long t0, t1, t2;
 240         int size, ret;
 241
 242         ret = -ENOMEM;
 243         src_page = alloc_page(GFP_KERNEL);
 244         if (!src_page)
 245                 goto no_src;
 246         dst_page = alloc_page(GFP_KERNEL);
 247         if (!dst_page)
 248                 goto no_dst;
 249         kernel_ptr = page_address(src_page);
 250         user_ptr = vmap(&dst_page, 1, VM_IOREMAP, __pgprot(__P010));
 251         if (!user_ptr)
 252                 goto no_vmap;
 253
 254         /* warm up the src page dcache */
 255         ret = __copy_to_user_memcpy(user_ptr, kernel_ptr, PAGE_SIZE);
 256
 257         for (size = PAGE_SIZE; size >= 4; size /= 2) {
 258                 t0 = sched_clock();
 259                 ret |= __copy_to_user_memcpy(user_ptr, kernel_ptr, size);
 260                 t1 = sched_clock();
 261                 ret |= __copy_to_user_std(user_ptr, kernel_ptr, size);
 262                 t2 = sched_clock();
 263                 printk("copy_to_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
 264         }
 265
 266         for (size = PAGE_SIZE; size >= 4; size /= 2) {
 267                 t0 = sched_clock();
 268                 ret |= __clear_user_memset(user_ptr, size);
 269                 t1 = sched_clock();
 270                 ret |= __clear_user_std(user_ptr, size);
 271                 t2 = sched_clock();
 272                 printk("clear_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
 273         }
 274
 275         if (ret)
 276                 ret = -EFAULT;
 277
 278         vunmap(user_ptr);
 279 no_vmap:
 280         put_page(dst_page);
 281 no_dst:
 282         put_page(src_page);
 283 no_src:
 284         return ret;
 285 }
 286
 287 subsys_initcall(test_size_treshold);
 288
 289 #endif