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                                 goto next;
  96                         /* fall through */
  97                 }
  98                 if (pmd_none_or_clear_bad(pmd))
  99                         goto next;
 100                 change_pte_range(vma->vm_mm, pmd, addr, next, newprot,
 101                                  dirty_accountable);
 102 next:
 103                 cond_resched();
 104         } while (pmd++, addr = next, addr != end);
 105 }
 106
 107 static inline void change_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
 108                 unsigned long addr, unsigned long end, pgprot_t newprot,
 109                 int dirty_accountable)
 110 {
 111         pud_t *pud;
 112         unsigned long next;
 113
 114         pud = pud_offset(pgd, addr);
 115         do {
 116                 next = pud_addr_end(addr, end);
 117                 if (pud_none_or_clear_bad(pud))
 118                         continue;
 119                 change_pmd_range(vma, pud, addr, next, newprot,
 120                                  dirty_accountable);
 121         } while (pud++, addr = next, addr != end);
 122 }
 123
 124 static void change_protection(struct vm_area_struct *vma,
 125                 unsigned long addr, unsigned long end, pgprot_t newprot,
 126                 int dirty_accountable)
 127 {
 128         struct mm_struct *mm = vma->vm_mm;
 129         pgd_t *pgd;
 130         unsigned long next;
 131         unsigned long start = addr;
 132
 133         BUG_ON(addr >= end);
 134         pgd = pgd_offset(mm, addr);
 135         flush_cache_range(vma, addr, end);
 136         do {
 137                 next = pgd_addr_end(addr, end);
 138                 if (pgd_none_or_clear_bad(pgd))
 139                         continue;
 140                 change_pud_range(vma, pgd, addr, next, newprot,
 141                                  dirty_accountable);
 142         } while (pgd++, addr = next, addr != end);
 143         flush_tlb_range(vma, start, end);
 144 }
 145
 146 int
 147 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 148         unsigned long start, unsigned long end, unsigned long newflags)
 149 {
 150         struct mm_struct *mm = vma->vm_mm;
 151         unsigned long oldflags = vma->vm_flags;
 152         long nrpages = (end - start) >> PAGE_SHIFT;
 153         unsigned long charged = 0;
 154         pgoff_t pgoff;
 155         int error;
 156         int dirty_accountable = 0;
 157
 158         if (newflags == oldflags) {
 159                 *pprev = vma;
 160                 return 0;
 161         }
 162
 163         /*
 164          * If we make a private mapping writable we increase our commit;
 165          * but (without finer accounting) cannot reduce our commit if we
 166          * make it unwritable again. hugetlb mapping were accounted for
 167          * even if read-only so there is no need to account for them here
 168          */
 169         if (newflags & VM_WRITE) {
 170                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
 171                                                 VM_SHARED|VM_NORESERVE))) {
 172                         charged = nrpages;
 173                         if (security_vm_enough_memory(charged))
 174                                 return -ENOMEM;
 175                         newflags |= VM_ACCOUNT;
 176                 }
 177         }
 178
 179         /*
 180          * First try to merge with previous and/or next vma.
 181          */
 182         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 183         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 184                         vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 185         if (*pprev) {
 186                 vma = *pprev;
 187                 goto success;
 188         }
 189
 190         *pprev = vma;
 191
 192         if (start != vma->vm_start) {
 193                 error = split_vma(mm, vma, start, 1);
 194                 if (error)
 195                         goto fail;
 196         }
 197
 198         if (end != vma->vm_end) {
 199                 error = split_vma(mm, vma, end, 0);
 200                 if (error)
 201                         goto fail;
 202         }
 203
 204 success:
 205         /*
 206          * vm_flags and vm_page_prot are protected by the mmap_sem
 207          * held in write mode.
 208          */
 209         vma->vm_flags = newflags;
 210         vma->vm_page_prot = pgprot_modify(vma->vm_page_prot,
 211                                           vm_get_page_prot(newflags));
 212
 213         if (vma_wants_writenotify(vma)) {
 214                 vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
 215                 dirty_accountable = 1;
 216         }
 217
 218         mmu_notifier_invalidate_range_start(mm, start, end);
 219         if (is_vm_hugetlb_page(vma))
 220                 hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
 221         else
 222                 change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
 223         mmu_notifier_invalidate_range_end(mm, start, end);
 224         vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 225         vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 226         perf_event_mmap(vma);
 227         return 0;
 228
 229 fail:
 230         vm_unacct_memory(charged);
 231         return error;
 232 }
 233
 234 SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 235                 unsigned long, prot)
 236 {
 237         unsigned long vm_flags, nstart, end, tmp, reqprot;
 238         struct vm_area_struct *vma, *prev;
 239         int error = -EINVAL;
 240         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 241         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 242         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 243                 return -EINVAL;
 244
 245         if (start & ~PAGE_MASK)
 246                 return -EINVAL;
 247         if (!len)
 248                 return 0;
 249         len = PAGE_ALIGN(len);
 250         end = start + len;
 251         if (end <= start)
 252                 return -ENOMEM;
 253         if (!arch_validate_prot(prot))
 254                 return -EINVAL;
 255
 256         reqprot = prot;
 257         /*
 258          * Does the application expect PROT_READ to imply PROT_EXEC:
 259          */
 260         if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
 261                 prot |= PROT_EXEC;
 262
 263         vm_flags = calc_vm_prot_bits(prot);
 264
 265         down_write(&current->mm->mmap_sem);
 266
 267         vma = find_vma_prev(current->mm, start, &prev);
 268         error = -ENOMEM;
 269         if (!vma)
 270                 goto out;
 271         if (unlikely(grows & PROT_GROWSDOWN)) {
 272                 if (vma->vm_start >= end)
 273                         goto out;
 274                 start = vma->vm_start;
 275                 error = -EINVAL;
 276                 if (!(vma->vm_flags & VM_GROWSDOWN))
 277                         goto out;
 278         }
 279         else {
 280                 if (vma->vm_start > start)
 281                         goto out;
 282                 if (unlikely(grows & PROT_GROWSUP)) {
 283                         end = vma->vm_end;
 284                         error = -EINVAL;
 285                         if (!(vma->vm_flags & VM_GROWSUP))
 286                                 goto out;
 287                 }
 288         }
 289         if (start > vma->vm_start)
 290                 prev = vma;
 291
 292         for (nstart = start ; ; ) {
 293                 unsigned long newflags;
 294
 295                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 296
 297                 newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 298
 299                 /* newflags >> 4 shift VM_MAY% in place of VM_% */
 300                 if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 301                         error = -EACCES;
 302                         goto out;
 303                 }
 304
 305                 error = security_file_mprotect(vma, reqprot, prot);
 306                 if (error)
 307                         goto out;
 308
 309                 tmp = vma->vm_end;
 310                 if (tmp > end)
 311                         tmp = end;
 312                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 313                 if (error)
 314                         goto out;
 315                 nstart = tmp;
 316
 317                 if (nstart < prev->vm_end)
 318                         nstart = prev->vm_end;
 319                 if (nstart >= end)
 320                         goto out;
 321
 322                 vma = prev->vm_next;
 323                 if (!vma || vma->vm_start != nstart) {
 324                         error = -ENOMEM;
 325                         goto out;
 326                 }
 327         }
 328 out:
 329         up_write(&current->mm->mmap_sem);
 330         return error;
 331 }