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