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 #ifndef pgprot_modify
  30 static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
  31 {
  32         return newprot;
  33 }
  34 #endif
  35
  36 static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
  37                 unsigned long addr, unsigned long end, pgprot_t newprot,
  38                 int dirty_accountable)
  39 {
  40         pte_t *pte, oldpte;
  41         spinlock_t *ptl;
  42
  43         pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
  44         arch_enter_lazy_mmu_mode();
  45         do {
  46                 oldpte = *pte;
  47                 if (pte_present(oldpte)) {
  48                         pte_t ptent;
  49
  50                         ptent = ptep_modify_prot_start(mm, addr, pte);
  51                         ptent = pte_modify(ptent, newprot);
  52
  53                         /*
  54                          * Avoid taking write faults for pages we know to be
  55                          * dirty.
  56                          */
  57                         if (dirty_accountable && pte_dirty(ptent))
  58                                 ptent = pte_mkwrite(ptent);
  59
  60                         ptep_modify_prot_commit(mm, addr, pte, ptent);
  61 #ifdef CONFIG_MIGRATION
  62                 } else if (!pte_file(oldpte)) {
  63                         swp_entry_t entry = pte_to_swp_entry(oldpte);
  64
  65                         if (is_write_migration_entry(entry)) {
  66                                 /*
  67                                  * A protection check is difficult so
  68                                  * just be safe and disable write
  69                                  */
  70                                 make_migration_entry_read(&entry);
  71                                 set_pte_at(mm, addr, pte,
  72                                         swp_entry_to_pte(entry));
  73                         }
  74 #endif
  75                 }
  76
  77         } while (pte++, addr += PAGE_SIZE, addr != end);
  78         arch_leave_lazy_mmu_mode();
  79         pte_unmap_unlock(pte - 1, ptl);
  80 }
  81
  82 static inline void change_pmd_range(struct mm_struct *mm, pud_t *pud,
  83                 unsigned long addr, unsigned long end, pgprot_t newprot,
  84                 int dirty_accountable)
  85 {
  86         pmd_t *pmd;
  87         unsigned long next;
  88
  89         pmd = pmd_offset(pud, addr);
  90         do {
  91                 next = pmd_addr_end(addr, end);
  92                 if (pmd_none_or_clear_bad(pmd))
  93                         continue;
  94                 change_pte_range(mm, pmd, addr, next, newprot, dirty_accountable);
  95         } while (pmd++, addr = next, addr != end);
  96 }
  97
  98 static inline void change_pud_range(struct mm_struct *mm, pgd_t *pgd,
  99                 unsigned long addr, unsigned long end, pgprot_t newprot,
 100                 int dirty_accountable)
 101 {
 102         pud_t *pud;
 103         unsigned long next;
 104
 105         pud = pud_offset(pgd, addr);
 106         do {
 107                 next = pud_addr_end(addr, end);
 108                 if (pud_none_or_clear_bad(pud))
 109                         continue;
 110                 change_pmd_range(mm, pud, addr, next, newprot, dirty_accountable);
 111         } while (pud++, addr = next, addr != end);
 112 }
 113
 114 static void change_protection(struct vm_area_struct *vma,
 115                 unsigned long addr, unsigned long end, pgprot_t newprot,
 116                 int dirty_accountable)
 117 {
 118         struct mm_struct *mm = vma->vm_mm;
 119         pgd_t *pgd;
 120         unsigned long next;
 121         unsigned long start = addr;
 122
 123         BUG_ON(addr >= end);
 124         pgd = pgd_offset(mm, addr);
 125         flush_cache_range(vma, addr, end);
 126         do {
 127                 next = pgd_addr_end(addr, end);
 128                 if (pgd_none_or_clear_bad(pgd))
 129                         continue;
 130                 change_pud_range(mm, pgd, addr, next, newprot, dirty_accountable);
 131         } while (pgd++, addr = next, addr != end);
 132         flush_tlb_range(vma, start, end);
 133 }
 134
 135 int
 136 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 137         unsigned long start, unsigned long end, unsigned long newflags)
 138 {
 139         struct mm_struct *mm = vma->vm_mm;
 140         unsigned long oldflags = vma->vm_flags;
 141         long nrpages = (end - start) >> PAGE_SHIFT;
 142         unsigned long charged = 0;
 143         pgoff_t pgoff;
 144         int error;
 145         int dirty_accountable = 0;
 146
 147         if (newflags == oldflags) {
 148                 *pprev = vma;
 149                 return 0;
 150         }
 151
 152         /*
 153          * If we make a private mapping writable we increase our commit;
 154          * but (without finer accounting) cannot reduce our commit if we
 155          * make it unwritable again.
 156          *
 157          * FIXME? We haven't defined a VM_NORESERVE flag, so mprotecting
 158          * a MAP_NORESERVE private mapping to writable will now reserve.
 159          */
 160         if (newflags & VM_WRITE) {
 161                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_SHARED))) {
 162                         charged = nrpages;
 163                         if (security_vm_enough_memory(charged))
 164                                 return -ENOMEM;
 165                         newflags |= VM_ACCOUNT;
 166                 }
 167         }
 168
 169         /*
 170          * First try to merge with previous and/or next vma.
 171          */
 172         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 173         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 174                         vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 175         if (*pprev) {
 176                 vma = *pprev;
 177                 goto success;
 178         }
 179
 180         *pprev = vma;
 181
 182         if (start != vma->vm_start) {
 183                 error = split_vma(mm, vma, start, 1);
 184                 if (error)
 185                         goto fail;
 186         }
 187
 188         if (end != vma->vm_end) {
 189                 error = split_vma(mm, vma, end, 0);
 190                 if (error)
 191                         goto fail;
 192         }
 193
 194 success:
 195         /*
 196          * vm_flags and vm_page_prot are protected by the mmap_sem
 197          * held in write mode.
 198          */
 199         vma->vm_flags = newflags;
 200         vma->vm_page_prot = pgprot_modify(vma->vm_page_prot,
 201                                           vm_get_page_prot(newflags));
 202
 203         if (vma_wants_writenotify(vma)) {
 204                 vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
 205                 dirty_accountable = 1;
 206         }
 207
 208         if (is_vm_hugetlb_page(vma))
 209                 hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
 210         else
 211                 change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
 212         vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 213         vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 214         return 0;
 215
 216 fail:
 217         vm_unacct_memory(charged);
 218         return error;
 219 }
 220
 221 asmlinkage long
 222 sys_mprotect(unsigned long start, size_t len, unsigned long prot)
 223 {
 224         unsigned long vm_flags, nstart, end, tmp, reqprot;
 225         struct vm_area_struct *vma, *prev;
 226         int error = -EINVAL;
 227         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 228         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 229         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 230                 return -EINVAL;
 231
 232         if (start & ~PAGE_MASK)
 233                 return -EINVAL;
 234         if (!len)
 235                 return 0;
 236         len = PAGE_ALIGN(len);
 237         end = start + len;
 238         if (end <= start)
 239                 return -ENOMEM;
 240         if (!arch_validate_prot(prot))
 241                 return -EINVAL;
 242
 243         reqprot = prot;
 244         /*
 245          * Does the application expect PROT_READ to imply PROT_EXEC:
 246          */
 247         if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
 248                 prot |= PROT_EXEC;
 249
 250         vm_flags = calc_vm_prot_bits(prot);
 251
 252         down_write(&current->mm->mmap_sem);
 253
 254         vma = find_vma_prev(current->mm, start, &prev);
 255         error = -ENOMEM;
 256         if (!vma)
 257                 goto out;
 258         if (unlikely(grows & PROT_GROWSDOWN)) {
 259                 if (vma->vm_start >= end)
 260                         goto out;
 261                 start = vma->vm_start;
 262                 error = -EINVAL;
 263                 if (!(vma->vm_flags & VM_GROWSDOWN))
 264                         goto out;
 265         }
 266         else {
 267                 if (vma->vm_start > start)
 268                         goto out;
 269                 if (unlikely(grows & PROT_GROWSUP)) {
 270                         end = vma->vm_end;
 271                         error = -EINVAL;
 272                         if (!(vma->vm_flags & VM_GROWSUP))
 273                                 goto out;
 274                 }
 275         }
 276         if (start > vma->vm_start)
 277                 prev = vma;
 278
 279         for (nstart = start ; ; ) {
 280                 unsigned long newflags;
 281
 282                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 283
 284                 newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 285
 286                 /* newflags >> 4 shift VM_MAY% in place of VM_% */
 287                 if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 288                         error = -EACCES;
 289                         goto out;
 290                 }
 291
 292                 error = security_file_mprotect(vma, reqprot, prot);
 293                 if (error)
 294                         goto out;
 295
 296                 tmp = vma->vm_end;
 297                 if (tmp > end)
 298                         tmp = end;
 299                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 300                 if (error)
 301                         goto out;
 302                 nstart = tmp;
 303
 304                 if (nstart < prev->vm_end)
 305                         nstart = prev->vm_end;
 306                 if (nstart >= end)
 307                         goto out;
 308
 309                 vma = prev->vm_next;
 310                 if (!vma || vma->vm_start != nstart) {
 311                         error = -ENOMEM;
 312                         goto out;
 313                 }
 314         }
 315 out:
 316         up_write(&current->mm->mmap_sem);
 317         return error;
 318 }