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
  23 #include <asm/uaccess.h>
  24 #include <asm/pgtable.h>
  25 #include <asm/pgalloc.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 {
  32         pte_t *pte;
  33
  34         pte = pte_offset_map(pmd, addr);
  35         do {
  36                 if (pte_present(*pte)) {
  37                         pte_t ptent;
  38
  39                         /* Avoid an SMP race with hardware updated dirty/clean
  40                          * bits by wiping the pte and then setting the new pte
  41                          * into place.
  42                          */
  43                         ptent = pte_modify(ptep_get_and_clear(mm, addr, pte), newprot);
  44                         set_pte_at(mm, addr, pte, ptent);
  45                         lazy_mmu_prot_update(ptent);
  46                 }
  47         } while (pte++, addr += PAGE_SIZE, addr != end);
  48         pte_unmap(pte - 1);
  49 }
  50
  51 static inline void change_pmd_range(struct mm_struct *mm, pud_t *pud,
  52                 unsigned long addr, unsigned long end, pgprot_t newprot)
  53 {
  54         pmd_t *pmd;
  55         unsigned long next;
  56
  57         pmd = pmd_offset(pud, addr);
  58         do {
  59                 next = pmd_addr_end(addr, end);
  60                 if (pmd_none_or_clear_bad(pmd))
  61                         continue;
  62                 change_pte_range(mm, pmd, addr, next, newprot);
  63         } while (pmd++, addr = next, addr != end);
  64 }
  65
  66 static inline void change_pud_range(struct mm_struct *mm, pgd_t *pgd,
  67                 unsigned long addr, unsigned long end, pgprot_t newprot)
  68 {
  69         pud_t *pud;
  70         unsigned long next;
  71
  72         pud = pud_offset(pgd, addr);
  73         do {
  74                 next = pud_addr_end(addr, end);
  75                 if (pud_none_or_clear_bad(pud))
  76                         continue;
  77                 change_pmd_range(mm, pud, addr, next, newprot);
  78         } while (pud++, addr = next, addr != end);
  79 }
  80
  81 static void change_protection(struct vm_area_struct *vma,
  82                 unsigned long addr, unsigned long end, pgprot_t newprot)
  83 {
  84         struct mm_struct *mm = vma->vm_mm;
  85         pgd_t *pgd;
  86         unsigned long next;
  87         unsigned long start = addr;
  88
  89         BUG_ON(addr >= end);
  90         pgd = pgd_offset(mm, addr);
  91         flush_cache_range(vma, addr, end);
  92         spin_lock(&mm->page_table_lock);
  93         do {
  94                 next = pgd_addr_end(addr, end);
  95                 if (pgd_none_or_clear_bad(pgd))
  96                         continue;
  97                 change_pud_range(mm, pgd, addr, next, newprot);
  98         } while (pgd++, addr = next, addr != end);
  99         flush_tlb_range(vma, start, end);
 100         spin_unlock(&mm->page_table_lock);
 101 }
 102
 103 static int
 104 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 105         unsigned long start, unsigned long end, unsigned long newflags)
 106 {
 107         struct mm_struct *mm = vma->vm_mm;
 108         unsigned long oldflags = vma->vm_flags;
 109         long nrpages = (end - start) >> PAGE_SHIFT;
 110         unsigned long charged = 0, old_end = vma->vm_end;
 111         pgprot_t newprot;
 112         pgoff_t pgoff;
 113         int error;
 114
 115         if (newflags == oldflags) {
 116                 *pprev = vma;
 117                 return 0;
 118         }
 119
 120         /*
 121          * If we make a private mapping writable we increase our commit;
 122          * but (without finer accounting) cannot reduce our commit if we
 123          * make it unwritable again.
 124          *
 125          * FIXME? We haven't defined a VM_NORESERVE flag, so mprotecting
 126          * a MAP_NORESERVE private mapping to writable will now reserve.
 127          */
 128         if (newflags & VM_WRITE) {
 129                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_SHARED|VM_HUGETLB))) {
 130                         charged = nrpages;
 131                         if (security_vm_enough_memory(charged))
 132                                 return -ENOMEM;
 133                         newflags |= VM_ACCOUNT;
 134                 }
 135         }
 136
 137         newprot = protection_map[newflags & 0xf];
 138
 139         /*
 140          * First try to merge with previous and/or next vma.
 141          */
 142         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 143         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 144                         vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 145         if (*pprev) {
 146                 vma = *pprev;
 147                 goto success;
 148         }
 149
 150         *pprev = vma;
 151
 152         if (start != vma->vm_start) {
 153                 error = split_vma(mm, vma, start, 1);
 154                 if (error)
 155                         goto fail;
 156         }
 157
 158         if (end != vma->vm_end) {
 159                 error = split_vma(mm, vma, end, 0);
 160                 if (error)
 161                         goto fail;
 162         }
 163
 164 success:
 165         /*
 166          * vm_flags and vm_page_prot are protected by the mmap_sem
 167          * held in write mode.
 168          */
 169         vma->vm_flags = newflags;
 170         vma->vm_page_prot = newprot;
 171         if (oldflags & VM_EXEC)
 172                 arch_remove_exec_range(current->mm, old_end);
 173         change_protection(vma, start, end, newprot);
 174         __vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 175         __vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 176         return 0;
 177
 178 fail:
 179         vm_unacct_memory(charged);
 180         return error;
 181 }
 182
 183 asmlinkage long
 184 sys_mprotect(unsigned long start, size_t len, unsigned long prot)
 185 {
 186         unsigned long vm_flags, nstart, end, tmp, reqprot;
 187         struct vm_area_struct *vma, *prev;
 188         int error = -EINVAL;
 189         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 190         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 191         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 192                 return -EINVAL;
 193
 194         if (start & ~PAGE_MASK)
 195                 return -EINVAL;
 196         if (!len)
 197                 return 0;
 198         len = PAGE_ALIGN(len);
 199         end = start + len;
 200         if (end <= start)
 201                 return -ENOMEM;
 202         if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM))
 203                 return -EINVAL;
 204
 205         reqprot = prot;
 206         /*
 207          * Does the application expect PROT_READ to imply PROT_EXEC:
 208          */
 209         if (unlikely((prot & PROT_READ) &&
 210                         (current->personality & READ_IMPLIES_EXEC)))
 211                 prot |= PROT_EXEC;
 212
 213         vm_flags = calc_vm_prot_bits(prot);
 214
 215         down_write(&current->mm->mmap_sem);
 216
 217         vma = find_vma_prev(current->mm, start, &prev);
 218         error = -ENOMEM;
 219         if (!vma)
 220                 goto out;
 221         if (unlikely(grows & PROT_GROWSDOWN)) {
 222                 if (vma->vm_start >= end)
 223                         goto out;
 224                 start = vma->vm_start;
 225                 error = -EINVAL;
 226                 if (!(vma->vm_flags & VM_GROWSDOWN))
 227                         goto out;
 228         }
 229         else {
 230                 if (vma->vm_start > start)
 231                         goto out;
 232                 if (unlikely(grows & PROT_GROWSUP)) {
 233                         end = vma->vm_end;
 234                         error = -EINVAL;
 235                         if (!(vma->vm_flags & VM_GROWSUP))
 236                                 goto out;
 237                 }
 238         }
 239         if (start > vma->vm_start)
 240                 prev = vma;
 241
 242         for (nstart = start ; ; ) {
 243                 unsigned long newflags;
 244
 245                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 246
 247                 if (is_vm_hugetlb_page(vma)) {
 248                         error = -EACCES;
 249                         goto out;
 250                 }
 251
 252                 newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 253
 254                 if ((newflags & ~(newflags >> 4)) & 0xf) {
 255                         error = -EACCES;
 256                         goto out;
 257                 }
 258
 259                 error = security_file_mprotect(vma, reqprot, prot);
 260                 if (error)
 261                         goto out;
 262
 263                 tmp = vma->vm_end;
 264                 if (tmp > end)
 265                         tmp = end;
 266                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 267                 if (error)
 268                         goto out;
 269                 nstart = tmp;
 270
 271                 if (nstart < prev->vm_end)
 272                         nstart = prev->vm_end;
 273                 if (nstart >= end)
 274                         goto out;
 275
 276                 vma = prev->vm_next;
 277                 if (!vma || vma->vm_start != nstart) {
 278                         error = -ENOMEM;
 279                         goto out;
 280                 }
 281         }
 282 out:
 283         up_write(&current->mm->mmap_sem);
 284         return error;
 285 }