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/shm.h>
  14 #include <linux/mman.h>
  15 #include <linux/fs.h>
  16 #include <linux/highmem.h>
  17 #include <linux/security.h>
  18 #include <linux/mempolicy.h>
  19 #include <linux/personality.h>
  20 #include <linux/syscalls.h>
  21 #include <linux/swap.h>
  22 #include <linux/swapops.h>
  23 #include <linux/mmu_notifier.h>
  24 #include <linux/migrate.h>
  25 #include <linux/perf_event.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 vm_area_struct *vma, 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_trans_huge(*pmd)) {
  92                         if (next - addr != HPAGE_PMD_SIZE)
  93                                 split_huge_page_pmd(vma->vm_mm, pmd);
  94                         else if (change_huge_pmd(vma, pmd, addr, newprot))
  95                                 continue;
  96                         /* fall through */
  97                 }
  98                 if (pmd_none_or_clear_bad(pmd))
  99                         continue;
 100                 change_pte_range(vma->vm_mm, pmd, addr, next, newprot,
 101                                  dirty_accountable);
 102         } while (pmd++, addr = next, addr != end);
 103 }
 104
 105 static inline void change_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
 106                 unsigned long addr, unsigned long end, pgprot_t newprot,
 107                 int dirty_accountable)
 108 {
 109         pud_t *pud;
 110         unsigned long next;
 111
 112         pud = pud_offset(pgd, addr);
 113         do {
 114                 next = pud_addr_end(addr, end);
 115                 if (pud_none_or_clear_bad(pud))
 116                         continue;
 117                 change_pmd_range(vma, pud, addr, next, newprot,
 118                                  dirty_accountable);
 119         } while (pud++, addr = next, addr != end);
 120 }
 121
 122 static void change_protection(struct vm_area_struct *vma,
 123                 unsigned long addr, unsigned long end, pgprot_t newprot,
 124                 int dirty_accountable)
 125 {
 126         struct mm_struct *mm = vma->vm_mm;
 127         pgd_t *pgd;
 128         unsigned long next;
 129         unsigned long start = addr;
 130
 131         BUG_ON(addr >= end);
 132         pgd = pgd_offset(mm, addr);
 133         flush_cache_range(vma, addr, end);
 134         do {
 135                 next = pgd_addr_end(addr, end);
 136                 if (pgd_none_or_clear_bad(pgd))
 137                         continue;
 138                 change_pud_range(vma, pgd, addr, next, newprot,
 139                                  dirty_accountable);
 140         } while (pgd++, addr = next, addr != end);
 141         flush_tlb_range(vma, start, end);
 142 }
 143
 144 int
 145 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 146         unsigned long start, unsigned long end, unsigned long newflags)
 147 {
 148         struct mm_struct *mm = vma->vm_mm;
 149         unsigned long oldflags = vma->vm_flags;
 150         long nrpages = (end - start) >> PAGE_SHIFT;
 151         unsigned long charged = 0;
 152         pgoff_t pgoff;
 153         int error;
 154         int dirty_accountable = 0;
 155
 156         if (newflags == oldflags) {
 157                 *pprev = vma;
 158                 return 0;
 159         }
 160
 161         /*
 162          * If we make a private mapping writable we increase our commit;
 163          * but (without finer accounting) cannot reduce our commit if we
 164          * make it unwritable again. hugetlb mapping were accounted for
 165          * even if read-only so there is no need to account for them here
 166          */
 167         if (newflags & VM_WRITE) {
 168                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
 169                                                 VM_SHARED|VM_NORESERVE))) {
 170                         charged = nrpages;
 171                         if (security_vm_enough_memory(charged))
 172                                 return -ENOMEM;
 173                         newflags |= VM_ACCOUNT;
 174                 }
 175         }
 176
 177         /*
 178          * First try to merge with previous and/or next vma.
 179          */
 180         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 181         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 182                         vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 183         if (*pprev) {
 184                 vma = *pprev;
 185                 goto success;
 186         }
 187
 188         *pprev = vma;
 189
 190         if (start != vma->vm_start) {
 191                 error = split_vma(mm, vma, start, 1);
 192                 if (error)
 193                         goto fail;
 194         }
 195
 196         if (end != vma->vm_end) {
 197                 error = split_vma(mm, vma, end, 0);
 198                 if (error)
 199                         goto fail;
 200         }
 201
 202 success:
 203         /*
 204          * vm_flags and vm_page_prot are protected by the mmap_sem
 205          * held in write mode.
 206          */
 207         vma->vm_flags = newflags;
 208         vma->vm_page_prot = pgprot_modify(vma->vm_page_prot,
 209                                           vm_get_page_prot(newflags));
 210
 211         if (vma_wants_writenotify(vma)) {
 212                 vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
 213                 dirty_accountable = 1;
 214         }
 215
 216         mmu_notifier_invalidate_range_start(mm, start, end);
 217         if (is_vm_hugetlb_page(vma))
 218                 hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
 219         else
 220                 change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
 221         mmu_notifier_invalidate_range_end(mm, start, end);
 222         vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 223         vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 224         perf_event_mmap(vma);
 225         return 0;
 226
 227 fail:
 228         vm_unacct_memory(charged);
 229         return error;
 230 }
 231
 232 SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 233                 unsigned long, prot)
 234 {
 235         unsigned long vm_flags, nstart, end, tmp, reqprot;
 236         struct vm_area_struct *vma, *prev;
 237         int error = -EINVAL;
 238         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 239         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 240         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 241                 return -EINVAL;
 242
 243         if (start & ~PAGE_MASK)
 244                 return -EINVAL;
 245         if (!len)
 246                 return 0;
 247         len = PAGE_ALIGN(len);
 248         end = start + len;
 249         if (end <= start)
 250                 return -ENOMEM;
 251         if (!arch_validate_prot(prot))
 252                 return -EINVAL;
 253
 254         reqprot = prot;
 255         /*
 256          * Does the application expect PROT_READ to imply PROT_EXEC:
 257          */
 258         if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
 259                 prot |= PROT_EXEC;
 260
 261         vm_flags = calc_vm_prot_bits(prot);
 262
 263         down_write(&current->mm->mmap_sem);
 264
 265         vma = find_vma_prev(current->mm, start, &prev);
 266         error = -ENOMEM;
 267         if (!vma)
 268                 goto out;
 269         if (unlikely(grows & PROT_GROWSDOWN)) {
 270                 if (vma->vm_start >= end)
 271                         goto out;
 272                 start = vma->vm_start;
 273                 error = -EINVAL;
 274                 if (!(vma->vm_flags & VM_GROWSDOWN))
 275                         goto out;
 276         }
 277         else {
 278                 if (vma->vm_start > start)
 279                         goto out;
 280                 if (unlikely(grows & PROT_GROWSUP)) {
 281                         end = vma->vm_end;
 282                         error = -EINVAL;
 283                         if (!(vma->vm_flags & VM_GROWSUP))
 284                                 goto out;
 285                 }
 286         }
 287         if (start > vma->vm_start)
 288                 prev = vma;
 289
 290         for (nstart = start ; ; ) {
 291                 unsigned long newflags;
 292
 293                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 294
 295                 newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 296
 297                 /* newflags >> 4 shift VM_MAY% in place of VM_% */
 298                 if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 299                         error = -EACCES;
 300                         goto out;
 301                 }
 302
 303                 error = security_file_mprotect(vma, reqprot, prot);
 304                 if (error)
 305                         goto out;
 306
 307                 tmp = vma->vm_end;
 308                 if (tmp > end)
 309                         tmp = end;
 310                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 311                 if (error)
 312                         goto out;
 313                 nstart = tmp;
 314
 315                 if (nstart < prev->vm_end)
 316                         nstart = prev->vm_end;
 317                 if (nstart >= end)
 318                         goto out;
 319
 320                 vma = prev->vm_next;
 321                 if (!vma || vma->vm_start != nstart) {
 322                         error = -ENOMEM;
 323                         goto out;
 324                 }
 325         }
 326 out:
 327         up_write(&current->mm->mmap_sem);
 328         return error;
 329 }