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/pgalloc.h>
  23 #include <asm/pgtable.h>
  24 #include <asm/pgalloc.h>
  25 #include <asm/cacheflush.h>
  26 #include <asm/tlbflush.h>
  27
  28 static inline void
  29 change_pte_range(pmd_t *pmd, unsigned long address,
  30                 unsigned long size, pgprot_t newprot)
  31 {
  32         pte_t * pte;
  33         unsigned long end;
  34
  35         if (pmd_none(*pmd))
  36                 return;
  37         if (pmd_bad(*pmd)) {
  38                 pmd_ERROR(*pmd);
  39                 pmd_clear(pmd);
  40                 return;
  41         }
  42         pte = pte_offset_map(pmd, address);
  43         address &= ~PMD_MASK;
  44         end = address + size;
  45         if (end > PMD_SIZE)
  46                 end = PMD_SIZE;
  47         do {
  48                 if (pte_present(*pte)) {
  49                         pte_t entry;
  50
  51                         /* Avoid an SMP race with hardware updated dirty/clean
  52                          * bits by wiping the pte and then setting the new pte
  53                          * into place.
  54                          */
  55                         entry = ptep_get_and_clear(pte);
  56                         set_pte(pte, pte_modify(entry, newprot));
  57                 }
  58                 address += PAGE_SIZE;
  59                 pte++;
  60         } while (address && (address < end));
  61         pte_unmap(pte - 1);
  62 }
  63
  64 static inline void
  65 change_pmd_range(pgd_t *pgd, unsigned long address,
  66                 unsigned long size, pgprot_t newprot)
  67 {
  68         pmd_t * pmd;
  69         unsigned long end;
  70
  71         if (pgd_none(*pgd))
  72                 return;
  73         if (pgd_bad(*pgd)) {
  74                 pgd_ERROR(*pgd);
  75                 pgd_clear(pgd);
  76                 return;
  77         }
  78         pmd = pmd_offset(pgd, address);
  79         address &= ~PGDIR_MASK;
  80         end = address + size;
  81         if (end > PGDIR_SIZE)
  82                 end = PGDIR_SIZE;
  83         do {
  84                 change_pte_range(pmd, address, end - address, newprot);
  85                 address = (address + PMD_SIZE) & PMD_MASK;
  86                 pmd++;
  87         } while (address && (address < end));
  88 }
  89
  90 static void
  91 change_protection(struct vm_area_struct *vma, unsigned long start,
  92                 unsigned long end, pgprot_t newprot)
  93 {
  94         pgd_t *dir;
  95         unsigned long beg = start;
  96
  97         dir = pgd_offset(current->mm, start);
  98         flush_cache_range(vma, beg, end);
  99         if (start >= end)
 100                 BUG();
 101         spin_lock(&current->mm->page_table_lock);
 102         do {
 103                 change_pmd_range(dir, start, end - start, newprot);
 104                 start = (start + PGDIR_SIZE) & PGDIR_MASK;
 105                 dir++;
 106         } while (start && (start < end));
 107         flush_tlb_range(vma, beg, end);
 108         spin_unlock(&current->mm->page_table_lock);
 109         return;
 110 }
 111
 112 static int
 113 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 114         unsigned long start, unsigned long end, unsigned int newflags)
 115 {
 116         struct mm_struct * mm = vma->vm_mm;
 117         unsigned long charged = 0, old_end = vma->vm_end;
 118         pgprot_t newprot;
 119         unsigned int oldflags;
 120         pgoff_t pgoff;
 121         int error;
 122
 123         if (newflags == vma->vm_flags) {
 124                 *pprev = vma;
 125                 return 0;
 126         }
 127
 128         /*
 129          * If we make a private mapping writable we increase our commit;
 130          * but (without finer accounting) cannot reduce our commit if we
 131          * make it unwritable again.
 132          *
 133          * FIXME? We haven't defined a VM_NORESERVE flag, so mprotecting
 134          * a MAP_NORESERVE private mapping to writable will now reserve.
 135          */
 136         if (newflags & VM_WRITE) {
 137                 if (!(vma->vm_flags & (VM_ACCOUNT|VM_WRITE|VM_SHARED|VM_HUGETLB))) {
 138                         charged = (end - start) >> PAGE_SHIFT;
 139                         if (security_vm_enough_memory(charged))
 140                                 return -ENOMEM;
 141                         newflags |= VM_ACCOUNT;
 142                 }
 143         }
 144
 145         newprot = protection_map[newflags & 0xf];
 146
 147         /*
 148          * First try to merge with previous and/or next vma.
 149          */
 150         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 151         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 152                         vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 153         if (*pprev) {
 154                 vma = *pprev;
 155                 goto success;
 156         }
 157
 158         if (start != vma->vm_start) {
 159                 error = split_vma(mm, vma, start, 1);
 160                 if (error)
 161                         goto fail;
 162         }
 163         /*
 164          * Unless it returns an error, this function always sets *pprev to
 165          * the first vma for which vma->vm_end >= end.
 166          */
 167         *pprev = vma;
 168
 169         if (end != vma->vm_end) {
 170                 error = split_vma(mm, vma, end, 0);
 171                 if (error)
 172                         goto fail;
 173         }
 174
 175 success:
 176         /*
 177          * vm_flags and vm_page_prot are protected by the mmap_sem
 178          * held in write mode.
 179          */
 180         oldflags = vma->vm_flags;
 181         vma->vm_flags = newflags;
 182         vma->vm_page_prot = newprot;
 183         if (oldflags & VM_EXEC)
 184                 arch_remove_exec_range(current->mm, old_end);
 185         change_protection(vma, start, end, newprot);
 186         return 0;
 187
 188 fail:
 189         vm_unacct_memory(charged);
 190         return error;
 191 }
 192
 193 asmlinkage long
 194 do_mprotect(struct mm_struct *mm, unsigned long start, size_t len,
 195              unsigned long prot)
 196 {
 197         unsigned long vm_flags, nstart, end, tmp;
 198         struct vm_area_struct *vma, *prev;
 199         int error = -EINVAL;
 200         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 201         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 202         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 203                 return -EINVAL;
 204
 205         if (start & ~PAGE_MASK)
 206                 return -EINVAL;
 207         len = PAGE_ALIGN(len);
 208         end = start + len;
 209         if (end < start)
 210                 return -ENOMEM;
 211         if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM))
 212                 return -EINVAL;
 213         if (end == start)
 214                 return 0;
 215
 216         vm_flags = calc_vm_prot_bits(prot);
 217
 218         down_write(&mm->mmap_sem);
 219
 220         vma = find_vma_prev(mm, start, &prev);
 221         error = -ENOMEM;
 222         if (!vma)
 223                 goto out;
 224         if (unlikely(grows & PROT_GROWSDOWN)) {
 225                 if (vma->vm_start >= end)
 226                         goto out;
 227                 start = vma->vm_start;
 228                 error = -EINVAL;
 229                 if (!(vma->vm_flags & VM_GROWSDOWN))
 230                         goto out;
 231         }
 232         else {
 233                 if (vma->vm_start > start)
 234                         goto out;
 235                 if (unlikely(grows & PROT_GROWSUP)) {
 236                         end = vma->vm_end;
 237                         error = -EINVAL;
 238                         if (!(vma->vm_flags & VM_GROWSUP))
 239                                 goto out;
 240                 }
 241         }
 242         if (start > vma->vm_start)
 243                 prev = vma;
 244
 245         for (nstart = start ; ; ) {
 246                 unsigned int newflags;
 247
 248                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 249
 250                 if (is_vm_hugetlb_page(vma)) {
 251                         error = -EACCES;
 252                         goto out;
 253                 }
 254
 255                 newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 256
 257                 if ((newflags & ~(newflags >> 4)) & 0xf) {
 258                         error = -EACCES;
 259                         goto out;
 260                 }
 261
 262                 error = security_file_mprotect(vma, prot);
 263                 if (error)
 264                         goto out;
 265
 266                 tmp = vma->vm_end;
 267                 if (tmp > end)
 268                         tmp = end;
 269                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 270                 if (error)
 271                         goto out;
 272                 nstart = tmp;
 273
 274                 if (nstart < prev->vm_end)
 275                         nstart = prev->vm_end;
 276                 if (nstart >= end)
 277                         goto out;
 278
 279                 vma = prev->vm_next;
 280                 if (!vma || vma->vm_start != nstart) {
 281                         error = -ENOMEM;
 282                         goto out;
 283                 }
 284         }
 285 out:
 286         up_write(&mm->mmap_sem);
 287         return error;
 288 }
 289
 290 asmlinkage long sys_mprotect(unsigned long start, size_t len, unsigned long prot)
 291 {
 292         return(do_mprotect(current->mm, start, len, prot));
 293 }