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@lxorguk.ukuu.org.uk>
   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 <linux/mmu_notifier.h>
  25 #include <linux/migrate.h>
  26 #include <asm/uaccess.h>
  27 #include <asm/pgtable.h>
  28 #include <asm/cacheflush.h>
  29 #include <asm/tlbflush.h>
  30
  31 #ifndef pgprot_modify
  32 static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
  33 {
  34         return newprot;
  35 }
  36 #endif
  37
  38 static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
  39                 unsigned long addr, unsigned long end, pgprot_t newprot,
  40                 int dirty_accountable)
  41 {
  42         pte_t *pte, oldpte;
  43         spinlock_t *ptl;
  44
  45         pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
  46         arch_enter_lazy_mmu_mode();
  47         do {
  48                 oldpte = *pte;
  49                 if (pte_present(oldpte)) {
  50                         pte_t ptent;
  51
  52                         ptent = ptep_modify_prot_start(mm, addr, pte);
  53                         ptent = pte_modify(ptent, newprot);
  54
  55                         /*
  56                          * Avoid taking write faults for pages we know to be
  57                          * dirty.
  58                          */
  59                         if (dirty_accountable && pte_dirty(ptent))
  60                                 ptent = pte_mkwrite(ptent);
  61
  62                         ptep_modify_prot_commit(mm, addr, pte, ptent);
  63                 } else if (PAGE_MIGRATION && !pte_file(oldpte)) {
  64                         swp_entry_t entry = pte_to_swp_entry(oldpte);
  65
  66                         if (is_write_migration_entry(entry)) {
  67                                 /*
  68                                  * A protection check is difficult so
  69                                  * just be safe and disable write
  70                                  */
  71                                 make_migration_entry_read(&entry);
  72                                 set_pte_at(mm, addr, pte,
  73                                         swp_entry_to_pte(entry));
  74                         }
  75                 }
  76         } while (pte++, addr += PAGE_SIZE, addr != end);
  77         arch_leave_lazy_mmu_mode();
  78         pte_unmap_unlock(pte - 1, ptl);
  79 }
  80
  81 static inline void change_pmd_range(struct mm_struct *mm, pud_t *pud,
  82                 unsigned long addr, unsigned long end, pgprot_t newprot,
  83                 int dirty_accountable)
  84 {
  85         pmd_t *pmd;
  86         unsigned long next;
  87
  88         pmd = pmd_offset(pud, addr);
  89         do {
  90                 next = pmd_addr_end(addr, end);
  91                 if (pmd_none_or_clear_bad(pmd))
  92                         continue;
  93                 change_pte_range(mm, pmd, addr, next, newprot, dirty_accountable);
  94         } while (pmd++, addr = next, addr != end);
  95 }
  96
  97 static inline void change_pud_range(struct mm_struct *mm, pgd_t *pgd,
  98                 unsigned long addr, unsigned long end, pgprot_t newprot,
  99                 int dirty_accountable)
 100 {
 101         pud_t *pud;
 102         unsigned long next;
 103
 104         pud = pud_offset(pgd, addr);
 105         do {
 106                 next = pud_addr_end(addr, end);
 107                 if (pud_none_or_clear_bad(pud))
 108                         continue;
 109                 change_pmd_range(mm, pud, addr, next, newprot, dirty_accountable);
 110         } while (pud++, addr = next, addr != end);
 111 }
 112
 113 static void change_protection(struct vm_area_struct *vma,
 114                 unsigned long addr, unsigned long end, pgprot_t newprot,
 115                 int dirty_accountable)
 116 {
 117         struct mm_struct *mm = vma->vm_mm;
 118         pgd_t *pgd;
 119         unsigned long next;
 120         unsigned long start = addr;
 121
 122         BUG_ON(addr >= end);
 123         pgd = pgd_offset(mm, addr);
 124         flush_cache_range(vma, addr, end);
 125         do {
 126                 next = pgd_addr_end(addr, end);
 127                 if (pgd_none_or_clear_bad(pgd))
 128                         continue;
 129                 change_pud_range(mm, pgd, addr, next, newprot, dirty_accountable);
 130         } while (pgd++, addr = next, addr != end);
 131         flush_tlb_range(vma, start, end);
 132 }
 133
 134 int
 135 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 136         unsigned long start, unsigned long end, unsigned long newflags)
 137 {
 138         struct mm_struct *mm = vma->vm_mm;
 139         unsigned long oldflags = vma->vm_flags;
 140         long nrpages = (end - start) >> PAGE_SHIFT;
 141         unsigned long charged = 0;
 142         pgoff_t pgoff;
 143         int error;
 144         int dirty_accountable = 0;
 145
 146         if (newflags == oldflags) {
 147                 *pprev = vma;
 148                 return 0;
 149         }
 150
 151         /*
 152          * If we make a private mapping writable we increase our commit;
 153          * but (without finer accounting) cannot reduce our commit if we
 154          * make it unwritable again.
 155          */
 156         if (newflags & VM_WRITE) {
 157                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|
 158                                                 VM_SHARED|VM_NORESERVE))) {
 159                         charged = nrpages;
 160                         if (security_vm_enough_memory(charged))
 161                                 return -ENOMEM;
 162                         newflags |= VM_ACCOUNT;
 163                 }
 164         }
 165
 166         /*
 167          * First try to merge with previous and/or next vma.
 168          */
 169         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 170         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 171                         vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 172         if (*pprev) {
 173                 vma = *pprev;
 174                 goto success;
 175         }
 176
 177         *pprev = vma;
 178
 179         if (start != vma->vm_start) {
 180                 error = split_vma(mm, vma, start, 1);
 181                 if (error)
 182                         goto fail;
 183         }
 184
 185         if (end != vma->vm_end) {
 186                 error = split_vma(mm, vma, end, 0);
 187                 if (error)
 188                         goto fail;
 189         }
 190
 191 success:
 192         /*
 193          * vm_flags and vm_page_prot are protected by the mmap_sem
 194          * held in write mode.
 195          */
 196         vma->vm_flags = newflags;
 197         vma->vm_page_prot = pgprot_modify(vma->vm_page_prot,
 198                                           vm_get_page_prot(newflags));
 199
 200         if (vma_wants_writenotify(vma)) {
 201                 vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
 202                 dirty_accountable = 1;
 203         }
 204
 205         mmu_notifier_invalidate_range_start(mm, start, end);
 206         if (is_vm_hugetlb_page(vma))
 207                 hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
 208         else
 209                 change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
 210         mmu_notifier_invalidate_range_end(mm, start, end);
 211         vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 212         vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 213         return 0;
 214
 215 fail:
 216         vm_unacct_memory(charged);
 217         return error;
 218 }
 219
 220 SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 221                 unsigned long, prot)
 222 {
 223         unsigned long vm_flags, nstart, end, tmp, reqprot;
 224         struct vm_area_struct *vma, *prev;
 225         int error = -EINVAL;
 226         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 227         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 228         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 229                 return -EINVAL;
 230
 231         if (start & ~PAGE_MASK)
 232                 return -EINVAL;
 233         if (!len)
 234                 return 0;
 235         len = PAGE_ALIGN(len);
 236         end = start + len;
 237         if (end <= start)
 238                 return -ENOMEM;
 239         if (!arch_validate_prot(prot))
 240                 return -EINVAL;
 241
 242         reqprot = prot;
 243         /*
 244          * Does the application expect PROT_READ to imply PROT_EXEC:
 245          */
 246         if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
 247                 prot |= PROT_EXEC;
 248
 249         vm_flags = calc_vm_prot_bits(prot);
 250
 251         down_write(&current->mm->mmap_sem);
 252
 253         vma = find_vma_prev(current->mm, start, &prev);
 254         error = -ENOMEM;
 255         if (!vma)
 256                 goto out;
 257         if (unlikely(grows & PROT_GROWSDOWN)) {
 258                 if (vma->vm_start >= end)
 259                         goto out;
 260                 start = vma->vm_start;
 261                 error = -EINVAL;
 262                 if (!(vma->vm_flags & VM_GROWSDOWN))
 263                         goto out;
 264         }
 265         else {
 266                 if (vma->vm_start > start)
 267                         goto out;
 268                 if (unlikely(grows & PROT_GROWSUP)) {
 269                         end = vma->vm_end;
 270                         error = -EINVAL;
 271                         if (!(vma->vm_flags & VM_GROWSUP))
 272                                 goto out;
 273                 }
 274         }
 275         if (start > vma->vm_start)
 276                 prev = vma;
 277
 278         for (nstart = start ; ; ) {
 279                 unsigned long newflags;
 280
 281                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 282
 283                 newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 284
 285                 /* newflags >> 4 shift VM_MAY% in place of VM_% */
 286                 if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 287                         error = -EACCES;
 288                         goto out;
 289                 }
 290
 291                 error = security_file_mprotect(vma, reqprot, prot);
 292                 if (error)
 293                         goto out;
 294
 295                 tmp = vma->vm_end;
 296                 if (tmp > end)
 297                         tmp = end;
 298                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 299                 if (error)
 300                         goto out;
 301                 nstart = tmp;
 302
 303                 if (nstart < prev->vm_end)
 304                         nstart = prev->vm_end;
 305                 if (nstart >= end)
 306                         goto out;
 307
 308                 vma = prev->vm_next;
 309                 if (!vma || vma->vm_start != nstart) {
 310                         error = -ENOMEM;
 311                         goto out;
 312                 }
 313         }
 314 out:
 315         up_write(&current->mm->mmap_sem);
 316         return error;
 317 }