mm/mprotect.c

   1 /*
   2  *  mm/mprotect.c
   3  *
   4  *  (C) Copyright 1994 Linus Torvalds
   5  *  (C) Copyright 2002 Christoph Hellwig
   6  *
   7  *  Address space accounting code       <alan@redhat.com>
   8  *  (C) Copyright 2002 Red Hat Inc, All Rights Reserved
   9  */
  10
  11 #include <linux/mm.h>
  12 #include <linux/hugetlb.h>
  13 #include <linux/slab.h>
  14 #include <linux/shm.h>
  15 #include <linux/mman.h>
  16 #include <linux/fs.h>
  17 #include <linux/highmem.h>
  18 #include <linux/security.h>
  19 #include <linux/mempolicy.h>
  20 #include <linux/personality.h>
  21 #include <linux/syscalls.h>
  22 #include <linux/swap.h>
  23 #include <linux/swapops.h>
  24 #include <asm/uaccess.h>
  25 #include <asm/pgtable.h>
  26 #include <asm/cacheflush.h>
  27 #include <asm/tlbflush.h>
  28
  29 static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
  30                 unsigned long addr, unsigned long end, pgprot_t newprot,
  31                 int dirty_accountable)
  32 {
  33         pte_t *pte, oldpte;
  34         spinlock_t *ptl;
  35
  36         pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
  37         arch_enter_lazy_mmu_mode();
  38         do {
  39                 oldpte = *pte;
  40                 if (pte_present(oldpte)) {
  41                         pte_t ptent;
  42
  43                         /* Avoid an SMP race with hardware updated dirty/clean
  44                          * bits by wiping the pte and then setting the new pte
  45                          * into place.
  46                          */
  47                         ptent = ptep_get_and_clear(mm, addr, pte);
  48                         ptent = pte_modify(ptent, newprot);
  49                         /*
  50                          * Avoid taking write faults for pages we know to be
  51                          * dirty.
  52                          */
  53                         if (dirty_accountable && pte_dirty(ptent))
  54                                 ptent = pte_mkwrite(ptent);
  55                         set_pte_at(mm, addr, pte, ptent);
  56 #ifdef CONFIG_MIGRATION
  57                 } else if (!pte_file(oldpte)) {
  58                         swp_entry_t entry = pte_to_swp_entry(oldpte);
  59
  60                         if (is_write_migration_entry(entry)) {
  61                                 /*
  62                                  * A protection check is difficult so
  63                                  * just be safe and disable write
  64                                  */
  65                                 make_migration_entry_read(&entry);
  66                                 set_pte_at(mm, addr, pte,
  67                                         swp_entry_to_pte(entry));
  68                         }
  69 #endif
  70                 }
  71
  72         } while (pte++, addr += PAGE_SIZE, addr != end);
  73         arch_leave_lazy_mmu_mode();
  74         pte_unmap_unlock(pte - 1, ptl);
  75 }
  76
  77 static inline void change_pmd_range(struct mm_struct *mm, pud_t *pud,
  78                 unsigned long addr, unsigned long end, pgprot_t newprot,
  79                 int dirty_accountable)
  80 {
  81         pmd_t *pmd;
  82         unsigned long next;
  83
  84         pmd = pmd_offset(pud, addr);
  85         do {
  86                 next = pmd_addr_end(addr, end);
  87                 if (pmd_none_or_clear_bad(pmd))
  88                         continue;
  89                 change_pte_range(mm, pmd, addr, next, newprot, dirty_accountable);
  90         } while (pmd++, addr = next, addr != end);
  91 }
  92
  93 static inline void change_pud_range(struct mm_struct *mm, pgd_t *pgd,
  94                 unsigned long addr, unsigned long end, pgprot_t newprot,
  95                 int dirty_accountable)
  96 {
  97         pud_t *pud;
  98         unsigned long next;
  99
 100         pud = pud_offset(pgd, addr);
 101         do {
 102                 next = pud_addr_end(addr, end);
 103                 if (pud_none_or_clear_bad(pud))
 104                         continue;
 105                 change_pmd_range(mm, pud, addr, next, newprot, dirty_accountable);
 106         } while (pud++, addr = next, addr != end);
 107 }
 108
 109 static void change_protection(struct vm_area_struct *vma,
 110                 unsigned long addr, unsigned long end, pgprot_t newprot,
 111                 int dirty_accountable)
 112 {
 113         struct mm_struct *mm = vma->vm_mm;
 114         pgd_t *pgd;
 115         unsigned long next;
 116         unsigned long start = addr;
 117
 118         BUG_ON(addr >= end);
 119         pgd = pgd_offset(mm, addr);
 120         flush_cache_range(vma, addr, end);
 121         do {
 122                 next = pgd_addr_end(addr, end);
 123                 if (pgd_none_or_clear_bad(pgd))
 124                         continue;
 125                 change_pud_range(mm, pgd, addr, next, newprot, dirty_accountable);
 126         } while (pgd++, addr = next, addr != end);
 127         flush_tlb_range(vma, start, end);
 128 }
 129
 130 int
 131 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 132         unsigned long start, unsigned long end, unsigned long newflags)
 133 {
 134         struct mm_struct *mm = vma->vm_mm;
 135         unsigned long oldflags = vma->vm_flags;
 136         long nrpages = (end - start) >> PAGE_SHIFT;
 137         unsigned long charged = 0;
 138         pgoff_t pgoff;
 139         int error;
 140         int dirty_accountable = 0;
 141
 142         if (newflags == oldflags) {
 143                 *pprev = vma;
 144                 return 0;
 145         }
 146
 147         /*
 148          * If we make a private mapping writable we increase our commit;
 149          * but (without finer accounting) cannot reduce our commit if we
 150          * make it unwritable again.
 151          *
 152          * FIXME? We haven't defined a VM_NORESERVE flag, so mprotecting
 153          * a MAP_NORESERVE private mapping to writable will now reserve.
 154          */
 155         if (newflags & VM_WRITE) {
 156                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_SHARED))) {
 157                         charged = nrpages;
 158                         if (security_vm_enough_memory(charged))
 159                                 return -ENOMEM;
 160                         newflags |= VM_ACCOUNT;
 161                 }
 162         }
 163
 164         /*
 165          * First try to merge with previous and/or next vma.
 166          */
 167         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 168         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 169                         vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 170         if (*pprev) {
 171                 vma = *pprev;
 172                 goto success;
 173         }
 174
 175         *pprev = vma;
 176
 177         if (start != vma->vm_start) {
 178                 error = split_vma(mm, vma, start, 1);
 179                 if (error)
 180                         goto fail;
 181         }
 182
 183         if (end != vma->vm_end) {
 184                 error = split_vma(mm, vma, end, 0);
 185                 if (error)
 186                         goto fail;
 187         }
 188
 189 success:
 190         /*
 191          * vm_flags and vm_page_prot are protected by the mmap_sem
 192          * held in write mode.
 193          */
 194         vma->vm_flags = newflags;
 195         vma->vm_page_prot = vm_get_page_prot(newflags);
 196         if (vma_wants_writenotify(vma)) {
 197                 vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
 198                 dirty_accountable = 1;
 199         }
 200
 201         if (is_vm_hugetlb_page(vma))
 202                 hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
 203         else
 204                 change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
 205         vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 206         vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 207         return 0;
 208
 209 fail:
 210         vm_unacct_memory(charged);
 211         return error;
 212 }
 213
 214 asmlinkage long
 215 sys_mprotect(unsigned long start, size_t len, unsigned long prot)
 216 {
 217         unsigned long vm_flags, nstart, end, tmp, reqprot;
 218         struct vm_area_struct *vma, *prev;
 219         int error = -EINVAL;
 220         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 221         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 222         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 223                 return -EINVAL;
 224
 225         if (start & ~PAGE_MASK)
 226                 return -EINVAL;
 227         if (!len)
 228                 return 0;
 229         len = PAGE_ALIGN(len);
 230         end = start + len;
 231         if (end <= start)
 232                 return -ENOMEM;
 233         if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM))
 234                 return -EINVAL;
 235
 236         reqprot = prot;
 237         /*
 238          * Does the application expect PROT_READ to imply PROT_EXEC:
 239          */
 240         if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
 241                 prot |= PROT_EXEC;
 242
 243         vm_flags = calc_vm_prot_bits(prot);
 244
 245         down_write(&current->mm->mmap_sem);
 246
 247         vma = find_vma_prev(current->mm, start, &prev);
 248         error = -ENOMEM;
 249         if (!vma)
 250                 goto out;
 251         if (unlikely(grows & PROT_GROWSDOWN)) {
 252                 if (vma->vm_start >= end)
 253                         goto out;
 254                 start = vma->vm_start;
 255                 error = -EINVAL;
 256                 if (!(vma->vm_flags & VM_GROWSDOWN))
 257                         goto out;
 258         }
 259         else {
 260                 if (vma->vm_start > start)
 261                         goto out;
 262                 if (unlikely(grows & PROT_GROWSUP)) {
 263                         end = vma->vm_end;
 264                         error = -EINVAL;
 265                         if (!(vma->vm_flags & VM_GROWSUP))
 266                                 goto out;
 267                 }
 268         }
 269         if (start > vma->vm_start)
 270                 prev = vma;
 271
 272         for (nstart = start ; ; ) {
 273                 unsigned long newflags;
 274
 275                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 276
 277                 newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 278
 279                 /* newflags >> 4 shift VM_MAY% in place of VM_% */
 280                 if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 281                         error = -EACCES;
 282                         goto out;
 283                 }
 284
 285                 error = security_file_mprotect(vma, reqprot, prot);
 286                 if (error)
 287                         goto out;
 288
 289                 tmp = vma->vm_end;
 290                 if (tmp > end)
 291                         tmp = end;
 292                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 293                 if (error)
 294                         goto out;
 295                 nstart = tmp;
 296
 297                 if (nstart < prev->vm_end)
 298                         nstart = prev->vm_end;
 299                 if (nstart >= end)
 300                         goto out;
 301
 302                 vma = prev->vm_next;
 303                 if (!vma || vma->vm_start != nstart) {
 304                         error = -ENOMEM;
 305                         goto out;
 306                 }
 307         }
 308 out:
 309         up_write(&current->mm->mmap_sem);
 310         return error;
 311 }