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
  21 #include <asm/uaccess.h>
  22 #include <asm/pgtable.h>
  23 #include <asm/pgalloc.h>
  24 #include <asm/cacheflush.h>
  25 #include <asm/tlbflush.h>
  26
  27 static inline void
  28 change_pte_range(pmd_t *pmd, unsigned long address,
  29                 unsigned long size, pgprot_t newprot)
  30 {
  31         pte_t * pte;
  32         unsigned long end;
  33
  34         if (pmd_none(*pmd))
  35                 return;
  36         if (pmd_bad(*pmd)) {
  37                 pmd_ERROR(*pmd);
  38                 pmd_clear(pmd);
  39                 return;
  40         }
  41         pte = pte_offset_map(pmd, address);
  42         address &= ~PMD_MASK;
  43         end = address + size;
  44         if (end > PMD_SIZE)
  45                 end = PMD_SIZE;
  46         do {
  47                 if (pte_present(*pte)) {
  48                         pte_t entry;
  49
  50                         /* Avoid an SMP race with hardware updated dirty/clean
  51                          * bits by wiping the pte and then setting the new pte
  52                          * into place.
  53                          */
  54                         entry = ptep_get_and_clear(pte);
  55                         set_pte(pte, pte_modify(entry, newprot));
  56                 }
  57                 address += PAGE_SIZE;
  58                 pte++;
  59         } while (address && (address < end));
  60         pte_unmap(pte - 1);
  61 }
  62
  63 static inline void
  64 change_pmd_range(pgd_t *pgd, unsigned long address,
  65                 unsigned long size, pgprot_t newprot)
  66 {
  67         pmd_t * pmd;
  68         unsigned long end;
  69
  70         if (pgd_none(*pgd))
  71                 return;
  72         if (pgd_bad(*pgd)) {
  73                 pgd_ERROR(*pgd);
  74                 pgd_clear(pgd);
  75                 return;
  76         }
  77         pmd = pmd_offset(pgd, address);
  78         address &= ~PGDIR_MASK;
  79         end = address + size;
  80         if (end > PGDIR_SIZE)
  81                 end = PGDIR_SIZE;
  82         do {
  83                 change_pte_range(pmd, address, end - address, newprot);
  84                 address = (address + PMD_SIZE) & PMD_MASK;
  85                 pmd++;
  86         } while (address && (address < end));
  87 }
  88
  89 static void
  90 change_protection(struct vm_area_struct *vma, unsigned long start,
  91                 unsigned long end, pgprot_t newprot)
  92 {
  93         pgd_t *dir;
  94         unsigned long beg = start;
  95
  96         dir = pgd_offset(current->mm, start);
  97         flush_cache_range(vma, beg, end);
  98         if (start >= end)
  99                 BUG();
 100         spin_lock(&current->mm->page_table_lock);
 101         do {
 102                 change_pmd_range(dir, start, end - start, newprot);
 103                 start = (start + PGDIR_SIZE) & PGDIR_MASK;
 104                 dir++;
 105         } while (start && (start < end));
 106         flush_tlb_range(vma, beg, end);
 107         spin_unlock(&current->mm->page_table_lock);
 108         return;
 109 }
 110
 111 static int
 112 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 113         unsigned long start, unsigned long end, unsigned int newflags)
 114 {
 115         struct mm_struct * mm = vma->vm_mm;
 116         unsigned long charged = 0, old_end = vma->vm_end;
 117         pgprot_t newprot;
 118         unsigned int oldflags;
 119         pgoff_t pgoff;
 120         int error;
 121
 122         if (newflags == vma->vm_flags) {
 123                 *pprev = vma;
 124                 return 0;
 125         }
 126
 127         /*
 128          * If we make a private mapping writable we increase our commit;
 129          * but (without finer accounting) cannot reduce our commit if we
 130          * make it unwritable again.
 131          *
 132          * FIXME? We haven't defined a VM_NORESERVE flag, so mprotecting
 133          * a MAP_NORESERVE private mapping to writable will now reserve.
 134          */
 135         if (newflags & VM_WRITE) {
 136                 if (!(vma->vm_flags & (VM_ACCOUNT|VM_WRITE|VM_SHARED|VM_HUGETLB))) {
 137                         charged = (end - start) >> PAGE_SHIFT;
 138                         if (security_vm_enough_memory(charged))
 139                                 return -ENOMEM;
 140                         newflags |= VM_ACCOUNT;
 141                 }
 142         }
 143
 144         newprot = protection_map[newflags & 0xf];
 145
 146         /*
 147          * First try to merge with previous and/or next vma.
 148          */
 149         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 150         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 151                         vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 152         if (*pprev) {
 153                 vma = *pprev;
 154                 goto success;
 155         }
 156
 157         if (start != vma->vm_start) {
 158                 error = split_vma(mm, vma, start, 1);
 159                 if (error)
 160                         goto fail;
 161         }
 162         /*
 163          * Unless it returns an error, this function always sets *pprev to
 164          * the first vma for which vma->vm_end >= end.
 165          */
 166         *pprev = vma;
 167
 168         if (end != vma->vm_end) {
 169                 error = split_vma(mm, vma, end, 0);
 170                 if (error)
 171                         goto fail;
 172         }
 173
 174 success:
 175         /*
 176          * vm_flags and vm_page_prot are protected by the mmap_sem
 177          * held in write mode.
 178          */
 179         oldflags = vma->vm_flags;
 180         vma->vm_flags = newflags;
 181         vma->vm_page_prot = newprot;
 182         if (oldflags & VM_EXEC)
 183                 arch_remove_exec_range(current->mm, old_end);
 184         change_protection(vma, start, end, newprot);
 185         return 0;
 186
 187 fail:
 188         vm_unacct_memory(charged);
 189         return error;
 190 }
 191
 192 asmlinkage long
 193 do_mprotect(struct mm_struct *mm, unsigned long start, size_t len,
 194              unsigned long prot)
 195 {
 196         unsigned long vm_flags, nstart, end, tmp;
 197         struct vm_area_struct *vma, *prev;
 198         int error = -EINVAL;
 199         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 200         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 201         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 202                 return -EINVAL;
 203
 204         if (start & ~PAGE_MASK)
 205                 return -EINVAL;
 206         len = PAGE_ALIGN(len);
 207         end = start + len;
 208         if (end < start)
 209                 return -ENOMEM;
 210         if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM))
 211                 return -EINVAL;
 212         if (end == start)
 213                 return 0;
 214
 215         vm_flags = calc_vm_prot_bits(prot);
 216
 217         down_write(&mm->mmap_sem);
 218
 219         vma = find_vma_prev(mm, start, &prev);
 220         error = -ENOMEM;
 221         if (!vma)
 222                 goto out;
 223         if (unlikely(grows & PROT_GROWSDOWN)) {
 224                 if (vma->vm_start >= end)
 225                         goto out;
 226                 start = vma->vm_start;
 227                 error = -EINVAL;
 228                 if (!(vma->vm_flags & VM_GROWSDOWN))
 229                         goto out;
 230         }
 231         else {
 232                 if (vma->vm_start > start)
 233                         goto out;
 234                 if (unlikely(grows & PROT_GROWSUP)) {
 235                         end = vma->vm_end;
 236                         error = -EINVAL;
 237                         if (!(vma->vm_flags & VM_GROWSUP))
 238                                 goto out;
 239                 }
 240         }
 241         if (start > vma->vm_start)
 242                 prev = vma;
 243
 244         for (nstart = start ; ; ) {
 245                 unsigned int newflags;
 246
 247                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 248
 249                 if (is_vm_hugetlb_page(vma)) {
 250                         error = -EACCES;
 251                         goto out;
 252                 }
 253
 254                 newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 255
 256                 if ((newflags & ~(newflags >> 4)) & 0xf) {
 257                         error = -EACCES;
 258                         goto out;
 259                 }
 260
 261                 error = security_file_mprotect(vma, prot);
 262                 if (error)
 263                         goto out;
 264
 265                 tmp = vma->vm_end;
 266                 if (tmp > end)
 267                         tmp = end;
 268                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 269                 if (error)
 270                         goto out;
 271                 nstart = tmp;
 272
 273                 if (nstart < prev->vm_end)
 274                         nstart = prev->vm_end;
 275                 if (nstart >= end)
 276                         goto out;
 277
 278                 vma = prev->vm_next;
 279                 if (!vma || vma->vm_start != nstart) {
 280                         error = -ENOMEM;
 281                         goto out;
 282                 }
 283         }
 284 out:
 285         up_write(&mm->mmap_sem);
 286         return error;
 287 }
 288
 289 asmlinkage long sys_mprotect(unsigned long start, size_t len, unsigned long prot)
 290 {
 291         return(do_mprotect(current->mm, start, len, prot));
 292 }