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                 int dirty_accountable)
  32 {
  33         pte_t *pte, oldpte;
  34         spinlock_t *ptl;
  35
  36         pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
  37         do {
  38                 oldpte = *pte;
  39                 if (pte_present(oldpte)) {
  40                         pte_t ptent;
  41
  42                         /* Avoid an SMP race with hardware updated dirty/clean
  43                          * bits by wiping the pte and then setting the new pte
  44                          * into place.
  45                          */
  46                         ptent = ptep_get_and_clear(mm, addr, pte);
  47                         ptent = pte_modify(ptent, newprot);
  48                         /*
  49                          * Avoid taking write faults for pages we know to be
  50                          * dirty.
  51                          */
  52                         if (dirty_accountable && pte_dirty(ptent))
  53                                 ptent = pte_mkwrite(ptent);
  54                         set_pte_at(mm, addr, pte, ptent);
  55                         lazy_mmu_prot_update(ptent);
  56 #ifdef CONFIG_MIGRATION
  57                 } else if (!pte_file(oldpte)) {
  58                         swp_entry_t entry = pte_to_swp_entry(oldpte);
  59
  60                         if (is_write_migration_entry(entry)) {
  61                                 /*
  62                                  * A protection check is difficult so
  63                                  * just be safe and disable write
  64                                  */
  65                                 make_migration_entry_read(&entry);
  66                                 set_pte_at(mm, addr, pte,
  67                                         swp_entry_to_pte(entry));
  68                         }
  69 #endif
  70                 }
  71
  72         } while (pte++, addr += PAGE_SIZE, addr != end);
  73         pte_unmap_unlock(pte - 1, ptl);
  74 }
  75
  76 static inline void change_pmd_range(struct mm_struct *mm, pud_t *pud,
  77                 unsigned long addr, unsigned long end, pgprot_t newprot,
  78                 int dirty_accountable)
  79 {
  80         pmd_t *pmd;
  81         unsigned long next;
  82
  83         pmd = pmd_offset(pud, addr);
  84         do {
  85                 next = pmd_addr_end(addr, end);
  86                 if (pmd_none_or_clear_bad(pmd))
  87                         continue;
  88                 change_pte_range(mm, pmd, addr, next, newprot, dirty_accountable);
  89         } while (pmd++, addr = next, addr != end);
  90 }
  91
  92 static inline void change_pud_range(struct mm_struct *mm, pgd_t *pgd,
  93                 unsigned long addr, unsigned long end, pgprot_t newprot,
  94                 int dirty_accountable)
  95 {
  96         pud_t *pud;
  97         unsigned long next;
  98
  99         pud = pud_offset(pgd, addr);
 100         do {
 101                 next = pud_addr_end(addr, end);
 102                 if (pud_none_or_clear_bad(pud))
 103                         continue;
 104                 change_pmd_range(mm, pud, addr, next, newprot, dirty_accountable);
 105         } while (pud++, addr = next, addr != end);
 106 }
 107
 108 static void change_protection(struct vm_area_struct *vma,
 109                 unsigned long addr, unsigned long end, pgprot_t newprot,
 110                 int dirty_accountable)
 111 {
 112         struct mm_struct *mm = vma->vm_mm;
 113         pgd_t *pgd;
 114         unsigned long next;
 115         unsigned long start = addr;
 116
 117         BUG_ON(addr >= end);
 118         pgd = pgd_offset(mm, addr);
 119         flush_cache_range(vma, addr, end);
 120         do {
 121                 next = pgd_addr_end(addr, end);
 122                 if (pgd_none_or_clear_bad(pgd))
 123                         continue;
 124                 change_pud_range(mm, pgd, addr, next, newprot, dirty_accountable);
 125         } while (pgd++, addr = next, addr != end);
 126         flush_tlb_range(vma, start, end);
 127 }
 128
 129 static int
 130 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 131         unsigned long start, unsigned long end, unsigned long newflags)
 132 {
 133         struct mm_struct *mm = vma->vm_mm;
 134         unsigned long oldflags = vma->vm_flags;
 135         long nrpages = (end - start) >> PAGE_SHIFT;
 136         unsigned long charged = 0;
 137         pgoff_t pgoff;
 138         int error;
 139         int dirty_accountable = 0;
 140
 141         if (newflags == oldflags) {
 142                 *pprev = vma;
 143                 return 0;
 144         }
 145
 146         /*
 147          * If we make a private mapping writable we increase our commit;
 148          * but (without finer accounting) cannot reduce our commit if we
 149          * make it unwritable again.
 150          *
 151          * FIXME? We haven't defined a VM_NORESERVE flag, so mprotecting
 152          * a MAP_NORESERVE private mapping to writable will now reserve.
 153          */
 154         if (newflags & VM_WRITE) {
 155                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_SHARED))) {
 156                         charged = nrpages;
 157                         if (security_vm_enough_memory(charged))
 158                                 return -ENOMEM;
 159                         newflags |= VM_ACCOUNT;
 160                 }
 161         }
 162
 163         /*
 164          * First try to merge with previous and/or next vma.
 165          */
 166         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 167         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 168                         vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 169         if (*pprev) {
 170                 vma = *pprev;
 171                 goto success;
 172         }
 173
 174         *pprev = vma;
 175
 176         if (start != vma->vm_start) {
 177                 error = split_vma(mm, vma, start, 1);
 178                 if (error)
 179                         goto fail;
 180         }
 181
 182         if (end != vma->vm_end) {
 183                 error = split_vma(mm, vma, end, 0);
 184                 if (error)
 185                         goto fail;
 186         }
 187
 188 success:
 189         /*
 190          * vm_flags and vm_page_prot are protected by the mmap_sem
 191          * held in write mode.
 192          */
 193         vma->vm_flags = newflags;
 194         vma->vm_page_prot = protection_map[newflags &
 195                 (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)];
 196         if (vma_wants_writenotify(vma)) {
 197                 vma->vm_page_prot = protection_map[newflags &
 198                         (VM_READ|VM_WRITE|VM_EXEC)];
 199                 dirty_accountable = 1;
 200         }
 201
 202         if (is_vm_hugetlb_page(vma))
 203                 hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
 204         else
 205                 change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
 206         vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 207         vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 208         return 0;
 209
 210 fail:
 211         vm_unacct_memory(charged);
 212         return error;
 213 }
 214
 215 asmlinkage long
 216 sys_mprotect(unsigned long start, size_t len, unsigned long prot)
 217 {
 218         unsigned long vm_flags, nstart, end, tmp, reqprot;
 219         struct vm_area_struct *vma, *prev;
 220         int error = -EINVAL;
 221         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 222         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 223         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 224                 return -EINVAL;
 225
 226         if (start & ~PAGE_MASK)
 227                 return -EINVAL;
 228         if (!len)
 229                 return 0;
 230         len = PAGE_ALIGN(len);
 231         end = start + len;
 232         if (end <= start)
 233                 return -ENOMEM;
 234         if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM))
 235                 return -EINVAL;
 236
 237         reqprot = prot;
 238         /*
 239          * Does the application expect PROT_READ to imply PROT_EXEC:
 240          */
 241         if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
 242                 prot |= PROT_EXEC;
 243
 244         vm_flags = calc_vm_prot_bits(prot);
 245
 246         down_write(&current->mm->mmap_sem);
 247
 248         vma = find_vma_prev(current->mm, start, &prev);
 249         error = -ENOMEM;
 250         if (!vma)
 251                 goto out;
 252         if (unlikely(grows & PROT_GROWSDOWN)) {
 253                 if (vma->vm_start >= end)
 254                         goto out;
 255                 start = vma->vm_start;
 256                 error = -EINVAL;
 257                 if (!(vma->vm_flags & VM_GROWSDOWN))
 258                         goto out;
 259         }
 260         else {
 261                 if (vma->vm_start > start)
 262                         goto out;
 263                 if (unlikely(grows & PROT_GROWSUP)) {
 264                         end = vma->vm_end;
 265                         error = -EINVAL;
 266                         if (!(vma->vm_flags & VM_GROWSUP))
 267                                 goto out;
 268                 }
 269         }
 270         if (start > vma->vm_start)
 271                 prev = vma;
 272
 273         for (nstart = start ; ; ) {
 274                 unsigned long newflags;
 275
 276                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 277
 278                 newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 279
 280                 /* newflags >> 4 shift VM_MAY% in place of VM_% */
 281                 if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 282                         error = -EACCES;
 283                         goto out;
 284                 }
 285
 286                 error = security_file_mprotect(vma, reqprot, prot);
 287                 if (error)
 288                         goto out;
 289
 290                 tmp = vma->vm_end;
 291                 if (tmp > end)
 292                         tmp = end;
 293                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 294                 if (error)
 295                         goto out;
 296                 nstart = tmp;
 297
 298                 if (nstart < prev->vm_end)
 299                         nstart = prev->vm_end;
 300                 if (nstart >= end)
 301                         goto out;
 302
 303                 vma = prev->vm_next;
 304                 if (!vma || vma->vm_start != nstart) {
 305                         error = -ENOMEM;
 306                         goto out;
 307                 }
 308         }
 309 out:
 310         up_write(&current->mm->mmap_sem);
 311         return error;
 312 }