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