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_leaf(*pmd))) {
  60                 ptl = &current->mm->page_table_lock;
  61                 spin_lock(ptl);
  62                 if (unlikely(!pmd_leaf(*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))
  78                 return 0;
  79
  80         if (unlikely(!pte_present(*pte) || !pte_young(*pte) ||
  81             !pte_write(*pte) || !pte_dirty(*pte))) {
  82                 pte_unmap_unlock(pte, ptl);
  83                 return 0;
  84         }
  85
  86         *ptep = pte;
  87         *ptlp = ptl;
  88
  89         return 1;
  90 }
  91
  92 static unsigned long noinline
  93 __copy_to_user_memcpy(void __user *to, const void *from, unsigned long n)
  94 {
  95         unsigned long ua_flags;
  96         int atomic;
  97
  98         /* the mmap semaphore is taken only if not in an atomic context */
  99         atomic = faulthandler_disabled();
 100
 101         if (!atomic)
 102                 mmap_read_lock(current->mm);
 103         while (n) {
 104                 pte_t *pte;
 105                 spinlock_t *ptl;
 106                 int tocopy;
 107
 108                 while (!pin_page_for_write(to, &pte, &ptl)) {
 109                         if (!atomic)
 110                                 mmap_read_unlock(current->mm);
 111                         if (__put_user(0, (char __user *)to))
 112                                 goto out;
 113                         if (!atomic)
 114                                 mmap_read_lock(current->mm);
 115                 }
 116
 117                 tocopy = (~(unsigned long)to & ~PAGE_MASK) + 1;
 118                 if (tocopy > n)
 119                         tocopy = n;
 120
 121                 ua_flags = uaccess_save_and_enable();
 122                 __memcpy((void *)to, from, tocopy);
 123                 uaccess_restore(ua_flags);
 124                 to += tocopy;
 125                 from += tocopy;
 126                 n -= tocopy;
 127
 128                 if (pte)
 129                         pte_unmap_unlock(pte, ptl);
 130                 else
 131                         spin_unlock(ptl);
 132         }
 133         if (!atomic)
 134                 mmap_read_unlock(current->mm);
 135
 136 out:
 137         return n;
 138 }
 139
 140 unsigned long
 141 arm_copy_to_user(void __user *to, const void *from, unsigned long n)
 142 {
 143         /*
 144          * This test is stubbed out of the main function above to keep
 145          * the overhead for small copies low by avoiding a large
 146          * register dump on the stack just to reload them right away.
 147          * With frame pointer disabled, tail call optimization kicks in
 148          * as well making this test almost invisible.
 149          */
 150         if (n < 64) {
 151                 unsigned long ua_flags = uaccess_save_and_enable();
 152                 n = __copy_to_user_std(to, from, n);
 153                 uaccess_restore(ua_flags);
 154         } else {
 155                 n = __copy_to_user_memcpy(uaccess_mask_range_ptr(to, n),
 156                                           from, n);
 157         }
 158         return n;
 159 }
 160
 161 static unsigned long noinline
 162 __clear_user_memset(void __user *addr, unsigned long n)
 163 {
 164         unsigned long ua_flags;
 165
 166         mmap_read_lock(current->mm);
 167         while (n) {
 168                 pte_t *pte;
 169                 spinlock_t *ptl;
 170                 int tocopy;
 171
 172                 while (!pin_page_for_write(addr, &pte, &ptl)) {
 173                         mmap_read_unlock(current->mm);
 174                         if (__put_user(0, (char __user *)addr))
 175                                 goto out;
 176                         mmap_read_lock(current->mm);
 177                 }
 178
 179                 tocopy = (~(unsigned long)addr & ~PAGE_MASK) + 1;
 180                 if (tocopy > n)
 181                         tocopy = n;
 182
 183                 ua_flags = uaccess_save_and_enable();
 184                 __memset((void *)addr, 0, tocopy);
 185                 uaccess_restore(ua_flags);
 186                 addr += tocopy;
 187                 n -= tocopy;
 188
 189                 if (pte)
 190                         pte_unmap_unlock(pte, ptl);
 191                 else
 192                         spin_unlock(ptl);
 193         }
 194         mmap_read_unlock(current->mm);
 195
 196 out:
 197         return n;
 198 }
 199
 200 unsigned long arm_clear_user(void __user *addr, unsigned long n)
 201 {
 202         /* See rational for this in __copy_to_user() above. */
 203         if (n < 64) {
 204                 unsigned long ua_flags = uaccess_save_and_enable();
 205                 n = __clear_user_std(addr, n);
 206                 uaccess_restore(ua_flags);
 207         } else {
 208                 n = __clear_user_memset(addr, n);
 209         }
 210         return n;
 211 }
 212
 213 #if 0
 214
 215 /*
 216  * This code is disabled by default, but kept around in case the chosen
 217  * thresholds need to be revalidated.  Some overhead (small but still)
 218  * would be implied by a runtime determined variable threshold, and
 219  * so far the measurement on concerned targets didn't show a worthwhile
 220  * variation.
 221  *
 222  * Note that a fairly precise sched_clock() implementation is needed
 223  * for results to make some sense.
 224  */
 225
 226 #include <linux/vmalloc.h>
 227
 228 static int __init test_size_treshold(void)
 229 {
 230         struct page *src_page, *dst_page;
 231         void *user_ptr, *kernel_ptr;
 232         unsigned long long t0, t1, t2;
 233         int size, ret;
 234
 235         ret = -ENOMEM;
 236         src_page = alloc_page(GFP_KERNEL);
 237         if (!src_page)
 238                 goto no_src;
 239         dst_page = alloc_page(GFP_KERNEL);
 240         if (!dst_page)
 241                 goto no_dst;
 242         kernel_ptr = page_address(src_page);
 243         user_ptr = vmap(&dst_page, 1, VM_IOREMAP, __pgprot(__PAGE_COPY));
 244         if (!user_ptr)
 245                 goto no_vmap;
 246
 247         /* warm up the src page dcache */
 248         ret = __copy_to_user_memcpy(user_ptr, kernel_ptr, PAGE_SIZE);
 249
 250         for (size = PAGE_SIZE; size >= 4; size /= 2) {
 251                 t0 = sched_clock();
 252                 ret |= __copy_to_user_memcpy(user_ptr, kernel_ptr, size);
 253                 t1 = sched_clock();
 254                 ret |= __copy_to_user_std(user_ptr, kernel_ptr, size);
 255                 t2 = sched_clock();
 256                 printk("copy_to_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
 257         }
 258
 259         for (size = PAGE_SIZE; size >= 4; size /= 2) {
 260                 t0 = sched_clock();
 261                 ret |= __clear_user_memset(user_ptr, size);
 262                 t1 = sched_clock();
 263                 ret |= __clear_user_std(user_ptr, size);
 264                 t2 = sched_clock();
 265                 printk("clear_user: %d %llu %llu\n", size, t1 - t0, t2 - t1);
 266         }
 267
 268         if (ret)
 269                 ret = -EFAULT;
 270
 271         vunmap(user_ptr);
 272 no_vmap:
 273         put_page(dst_page);
 274 no_dst:
 275         put_page(src_page);
 276 no_src:
 277         return ret;
 278 }
 279
 280 subsys_initcall(test_size_treshold);
 281
 282 #endif