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 inline void
  30 change_pte_range(pmd_t *pmd, unsigned long address,
  31                 unsigned long size, pgprot_t newprot)
  32 {
  33         pte_t * pte;
  34         unsigned long end;
  35
  36         if (pmd_none(*pmd))
  37                 return;
  38         if (pmd_bad(*pmd)) {
  39                 pmd_ERROR(*pmd);
  40                 pmd_clear(pmd);
  41                 return;
  42         }
  43         pte = pte_offset_map(pmd, address);
  44         address &= ~PMD_MASK;
  45         end = address + size;
  46         if (end > PMD_SIZE)
  47                 end = PMD_SIZE;
  48         do {
  49                 if (pte_present(*pte)) {
  50                         pte_t entry;
  51
  52                         /* Avoid an SMP race with hardware updated dirty/clean
  53                          * bits by wiping the pte and then setting the new pte
  54                          * into place.
  55                          */
  56                         entry = ptep_get_and_clear(pte);
  57                         set_pte(pte, pte_modify(entry, newprot));
  58                 }
  59                 address += PAGE_SIZE;
  60                 pte++;
  61         } while (address && (address < end));
  62         pte_unmap(pte - 1);
  63 }
  64
  65 static inline void
  66 change_pmd_range(pgd_t *pgd, unsigned long address,
  67                 unsigned long size, pgprot_t newprot)
  68 {
  69         pmd_t * pmd;
  70         unsigned long end;
  71
  72         if (pgd_none(*pgd))
  73                 return;
  74         if (pgd_bad(*pgd)) {
  75                 pgd_ERROR(*pgd);
  76                 pgd_clear(pgd);
  77                 return;
  78         }
  79         pmd = pmd_offset(pgd, address);
  80         address &= ~PGDIR_MASK;
  81         end = address + size;
  82         if (end > PGDIR_SIZE)
  83                 end = PGDIR_SIZE;
  84         do {
  85                 change_pte_range(pmd, address, end - address, newprot);
  86                 address = (address + PMD_SIZE) & PMD_MASK;
  87                 pmd++;
  88         } while (address && (address < end));
  89 }
  90
  91 static void
  92 change_protection(struct vm_area_struct *vma, unsigned long start,
  93                 unsigned long end, pgprot_t newprot)
  94 {
  95         pgd_t *dir;
  96         unsigned long beg = start;
  97
  98         dir = pgd_offset(current->mm, start);
  99         flush_cache_range(vma, beg, end);
 100         if (start >= end)
 101                 BUG();
 102         spin_lock(&current->mm->page_table_lock);
 103         do {
 104                 change_pmd_range(dir, start, end - start, newprot);
 105                 start = (start + PGDIR_SIZE) & PGDIR_MASK;
 106                 dir++;
 107         } while (start && (start < end));
 108         flush_tlb_range(vma, beg, end);
 109         spin_unlock(&current->mm->page_table_lock);
 110         return;
 111 }
 112
 113 static int
 114 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 115         unsigned long start, unsigned long end, unsigned long newflags)
 116 {
 117         struct mm_struct * mm = vma->vm_mm;
 118         unsigned long oldflags = vma->vm_flags;
 119         long nrpages = (end - start) >> PAGE_SHIFT;
 120         unsigned long charged = 0, old_end = vma->vm_end;
 121         pgprot_t newprot;
 122         pgoff_t pgoff;
 123         int error;
 124
 125         if (newflags == oldflags) {
 126                 *pprev = vma;
 127                 return 0;
 128         }
 129
 130         /*
 131          * If we make a private mapping writable we increase our commit;
 132          * but (without finer accounting) cannot reduce our commit if we
 133          * make it unwritable again.
 134          *
 135          * FIXME? We haven't defined a VM_NORESERVE flag, so mprotecting
 136          * a MAP_NORESERVE private mapping to writable will now reserve.
 137          */
 138         if (newflags & VM_WRITE) {
 139                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_SHARED|VM_HUGETLB))) {
 140                         charged = nrpages;
 141                         if (security_vm_enough_memory(charged))
 142                                 return -ENOMEM;
 143                         newflags |= VM_ACCOUNT;
 144                 }
 145         }
 146
 147         newprot = protection_map[newflags & 0xf];
 148
 149         /*
 150          * First try to merge with previous and/or next vma.
 151          */
 152         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 153         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 154                         vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 155         if (*pprev) {
 156                 vma = *pprev;
 157                 goto success;
 158         }
 159
 160         if (start != vma->vm_start) {
 161                 error = split_vma(mm, vma, start, 1);
 162                 if (error)
 163                         goto fail;
 164         }
 165         /*
 166          * Unless it returns an error, this function always sets *pprev to
 167          * the first vma for which vma->vm_end >= end.
 168          */
 169         *pprev = vma;
 170
 171         if (end != vma->vm_end) {
 172                 error = split_vma(mm, vma, end, 0);
 173                 if (error)
 174                         goto fail;
 175         }
 176
 177 success:
 178         /*
 179          * vm_flags and vm_page_prot are protected by the mmap_sem
 180          * held in write mode.
 181          */
 182         oldflags = vma->vm_flags;
 183         vma->vm_flags = newflags;
 184         vma->vm_page_prot = newprot;
 185         if (oldflags & VM_EXEC)
 186                 arch_remove_exec_range(current->mm, old_end);
 187         change_protection(vma, start, end, newprot);
 188         __vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 189         __vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 190         return 0;
 191
 192 fail:
 193         vm_unacct_memory(charged);
 194         return error;
 195 }
 196
 197 asmlinkage long
 198 do_mprotect(struct mm_struct *mm, unsigned long start, size_t len,
 199              unsigned long prot)
 200 {
 201         unsigned long vm_flags, nstart, end, tmp;
 202         struct vm_area_struct *vma, *prev;
 203         int error = -EINVAL;
 204         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 205         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 206         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 207                 return -EINVAL;
 208
 209         if (start & ~PAGE_MASK)
 210                 return -EINVAL;
 211         len = PAGE_ALIGN(len);
 212         end = start + len;
 213         if (end < start)
 214                 return -ENOMEM;
 215         if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM))
 216                 return -EINVAL;
 217         if (end == start)
 218                 return 0;
 219         /*
 220          * Does the application expect PROT_READ to imply PROT_EXEC:
 221          */
 222         if (unlikely((prot & PROT_READ) &&
 223                         (current->personality & READ_IMPLIES_EXEC)))
 224                 prot |= PROT_EXEC;
 225
 226         vm_flags = calc_vm_prot_bits(prot);
 227
 228         down_write(&mm->mmap_sem);
 229
 230         vma = find_vma_prev(mm, start, &prev);
 231         error = -ENOMEM;
 232         if (!vma)
 233                 goto out;
 234         if (unlikely(grows & PROT_GROWSDOWN)) {
 235                 if (vma->vm_start >= end)
 236                         goto out;
 237                 start = vma->vm_start;
 238                 error = -EINVAL;
 239                 if (!(vma->vm_flags & VM_GROWSDOWN))
 240                         goto out;
 241         }
 242         else {
 243                 if (vma->vm_start > start)
 244                         goto out;
 245                 if (unlikely(grows & PROT_GROWSUP)) {
 246                         end = vma->vm_end;
 247                         error = -EINVAL;
 248                         if (!(vma->vm_flags & VM_GROWSUP))
 249                                 goto out;
 250                 }
 251         }
 252         if (start > vma->vm_start)
 253                 prev = vma;
 254
 255         for (nstart = start ; ; ) {
 256                 unsigned long newflags;
 257
 258                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 259
 260                 if (is_vm_hugetlb_page(vma)) {
 261                         error = -EACCES;
 262                         goto out;
 263                 }
 264
 265                 newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 266
 267                 if ((newflags & ~(newflags >> 4)) & 0xf) {
 268                         error = -EACCES;
 269                         goto out;
 270                 }
 271
 272                 error = security_file_mprotect(vma, prot);
 273                 if (error)
 274                         goto out;
 275
 276                 tmp = vma->vm_end;
 277                 if (tmp > end)
 278                         tmp = end;
 279                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 280                 if (error)
 281                         goto out;
 282                 nstart = tmp;
 283
 284                 if (nstart < prev->vm_end)
 285                         nstart = prev->vm_end;
 286                 if (nstart >= end)
 287                         goto out;
 288
 289                 vma = prev->vm_next;
 290                 if (!vma || vma->vm_start != nstart) {
 291                         error = -ENOMEM;
 292                         goto out;
 293                 }
 294         }
 295 out:
 296         up_write(&mm->mmap_sem);
 297         return error;
 298 }
 299
 300 asmlinkage long sys_mprotect(unsigned long start, size_t len, unsigned long prot)
 301 {
 302         return(do_mprotect(current->mm, start, len, prot));
 303 }