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         pgoff_t pgoff;
 127         int error;
 128
 129         if (newflags == oldflags) {
 130                 *pprev = vma;
 131                 return 0;
 132         }
 133
 134         /*
 135          * If we make a private mapping writable we increase our commit;
 136          * but (without finer accounting) cannot reduce our commit if we
 137          * make it unwritable again.
 138          *
 139          * FIXME? We haven't defined a VM_NORESERVE flag, so mprotecting
 140          * a MAP_NORESERVE private mapping to writable will now reserve.
 141          */
 142         if (newflags & VM_WRITE) {
 143                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_SHARED))) {
 144                         charged = nrpages;
 145                         if (security_vm_enough_memory(charged))
 146                                 return -ENOMEM;
 147                         newflags |= VM_ACCOUNT;
 148                 }
 149         }
 150
 151         /*
 152          * First try to merge with previous and/or next vma.
 153          */
 154         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 155         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 156                         vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 157         if (*pprev) {
 158                 vma = *pprev;
 159                 goto success;
 160         }
 161
 162         *pprev = vma;
 163
 164         if (start != vma->vm_start) {
 165                 error = split_vma(mm, vma, start, 1);
 166                 if (error)
 167                         goto fail;
 168         }
 169
 170         if (end != vma->vm_end) {
 171                 error = split_vma(mm, vma, end, 0);
 172                 if (error)
 173                         goto fail;
 174         }
 175
 176 success:
 177         /*
 178          * vm_flags and vm_page_prot are protected by the mmap_sem
 179          * held in write mode.
 180          */
 181         vma->vm_flags = newflags;
 182         vma->vm_page_prot = protection_map[newflags &
 183                 (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)];
 184         if (vma_wants_writenotify(vma))
 185                 vma->vm_page_prot = protection_map[newflags &
 186                         (VM_READ|VM_WRITE|VM_EXEC)];
 187
 188         if (is_vm_hugetlb_page(vma))
 189                 hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
 190         else
 191                 change_protection(vma, start, end, vma->vm_page_prot);
 192         vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 193         vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 194         return 0;
 195
 196 fail:
 197         vm_unacct_memory(charged);
 198         return error;
 199 }
 200
 201 asmlinkage long
 202 sys_mprotect(unsigned long start, size_t len, unsigned long prot)
 203 {
 204         unsigned long vm_flags, nstart, end, tmp, reqprot;
 205         struct vm_area_struct *vma, *prev;
 206         int error = -EINVAL;
 207         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 208         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 209         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 210                 return -EINVAL;
 211
 212         if (start & ~PAGE_MASK)
 213                 return -EINVAL;
 214         if (!len)
 215                 return 0;
 216         len = PAGE_ALIGN(len);
 217         end = start + len;
 218         if (end <= start)
 219                 return -ENOMEM;
 220         if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM))
 221                 return -EINVAL;
 222
 223         reqprot = prot;
 224         /*
 225          * Does the application expect PROT_READ to imply PROT_EXEC:
 226          */
 227         if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
 228                 prot |= PROT_EXEC;
 229
 230         vm_flags = calc_vm_prot_bits(prot);
 231
 232         down_write(&current->mm->mmap_sem);
 233
 234         vma = find_vma_prev(current->mm, start, &prev);
 235         error = -ENOMEM;
 236         if (!vma)
 237                 goto out;
 238         if (unlikely(grows & PROT_GROWSDOWN)) {
 239                 if (vma->vm_start >= end)
 240                         goto out;
 241                 start = vma->vm_start;
 242                 error = -EINVAL;
 243                 if (!(vma->vm_flags & VM_GROWSDOWN))
 244                         goto out;
 245         }
 246         else {
 247                 if (vma->vm_start > start)
 248                         goto out;
 249                 if (unlikely(grows & PROT_GROWSUP)) {
 250                         end = vma->vm_end;
 251                         error = -EINVAL;
 252                         if (!(vma->vm_flags & VM_GROWSUP))
 253                                 goto out;
 254                 }
 255         }
 256         if (start > vma->vm_start)
 257                 prev = vma;
 258
 259         for (nstart = start ; ; ) {
 260                 unsigned long newflags;
 261
 262                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 263
 264                 newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 265
 266                 /* newflags >> 4 shift VM_MAY% in place of VM_% */
 267                 if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 268                         error = -EACCES;
 269                         goto out;
 270                 }
 271
 272                 error = security_file_mprotect(vma, reqprot, 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(&current->mm->mmap_sem);
 297         return error;
 298 }