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 <linux/mmu_notifier.h>
  25 #include <asm/uaccess.h>
  26 #include <asm/pgtable.h>
  27 #include <asm/cacheflush.h>
  28 #include <asm/tlbflush.h>
  29
  30 #ifndef pgprot_modify
  31 static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
  32 {
  33         return newprot;
  34 }
  35 #endif
  36
  37 static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
  38                 unsigned long addr, unsigned long end, pgprot_t newprot,
  39                 int dirty_accountable)
  40 {
  41         pte_t *pte, oldpte;
  42         spinlock_t *ptl;
  43
  44         pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
  45         arch_enter_lazy_mmu_mode();
  46         do {
  47                 oldpte = *pte;
  48                 if (pte_present(oldpte)) {
  49                         pte_t ptent;
  50
  51                         ptent = ptep_modify_prot_start(mm, addr, pte);
  52                         ptent = pte_modify(ptent, newprot);
  53
  54                         /*
  55                          * Avoid taking write faults for pages we know to be
  56                          * dirty.
  57                          */
  58                         if (dirty_accountable && pte_dirty(ptent))
  59                                 ptent = pte_mkwrite(ptent);
  60
  61                         ptep_modify_prot_commit(mm, addr, pte, ptent);
  62 #ifdef CONFIG_MIGRATION
  63                 } else if (!pte_file(oldpte)) {
  64                         swp_entry_t entry = pte_to_swp_entry(oldpte);
  65
  66                         if (is_write_migration_entry(entry)) {
  67                                 /*
  68                                  * A protection check is difficult so
  69                                  * just be safe and disable write
  70                                  */
  71                                 make_migration_entry_read(&entry);
  72                                 set_pte_at(mm, addr, pte,
  73                                         swp_entry_to_pte(entry));
  74                         }
  75 #endif
  76                 }
  77
  78         } while (pte++, addr += PAGE_SIZE, addr != end);
  79         arch_leave_lazy_mmu_mode();
  80         pte_unmap_unlock(pte - 1, ptl);
  81 }
  82
  83 static inline void change_pmd_range(struct mm_struct *mm, pud_t *pud,
  84                 unsigned long addr, unsigned long end, pgprot_t newprot,
  85                 int dirty_accountable)
  86 {
  87         pmd_t *pmd;
  88         unsigned long next;
  89
  90         pmd = pmd_offset(pud, addr);
  91         do {
  92                 next = pmd_addr_end(addr, end);
  93                 if (pmd_none_or_clear_bad(pmd))
  94                         continue;
  95                 change_pte_range(mm, pmd, addr, next, newprot, dirty_accountable);
  96         } while (pmd++, addr = next, addr != end);
  97 }
  98
  99 static inline void change_pud_range(struct mm_struct *mm, pgd_t *pgd,
 100                 unsigned long addr, unsigned long end, pgprot_t newprot,
 101                 int dirty_accountable)
 102 {
 103         pud_t *pud;
 104         unsigned long next;
 105
 106         pud = pud_offset(pgd, addr);
 107         do {
 108                 next = pud_addr_end(addr, end);
 109                 if (pud_none_or_clear_bad(pud))
 110                         continue;
 111                 change_pmd_range(mm, pud, addr, next, newprot, dirty_accountable);
 112         } while (pud++, addr = next, addr != end);
 113 }
 114
 115 static void change_protection(struct vm_area_struct *vma,
 116                 unsigned long addr, unsigned long end, pgprot_t newprot,
 117                 int dirty_accountable)
 118 {
 119         struct mm_struct *mm = vma->vm_mm;
 120         pgd_t *pgd;
 121         unsigned long next;
 122         unsigned long start = addr;
 123
 124         BUG_ON(addr >= end);
 125         pgd = pgd_offset(mm, addr);
 126         flush_cache_range(vma, addr, end);
 127         do {
 128                 next = pgd_addr_end(addr, end);
 129                 if (pgd_none_or_clear_bad(pgd))
 130                         continue;
 131                 change_pud_range(mm, pgd, addr, next, newprot, dirty_accountable);
 132         } while (pgd++, addr = next, addr != end);
 133         flush_tlb_range(vma, start, end);
 134 }
 135
 136 int
 137 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 138         unsigned long start, unsigned long end, unsigned long newflags)
 139 {
 140         struct mm_struct *mm = vma->vm_mm;
 141         unsigned long oldflags = vma->vm_flags;
 142         long nrpages = (end - start) >> PAGE_SHIFT;
 143         unsigned long charged = 0;
 144         pgoff_t pgoff;
 145         int error;
 146         int dirty_accountable = 0;
 147
 148         if (newflags == oldflags) {
 149                 *pprev = vma;
 150                 return 0;
 151         }
 152
 153         /*
 154          * If we make a private mapping writable we increase our commit;
 155          * but (without finer accounting) cannot reduce our commit if we
 156          * make it unwritable again.
 157          */
 158         if (newflags & VM_WRITE) {
 159                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|
 160                                                 VM_SHARED|VM_NORESERVE))) {
 161                         charged = nrpages;
 162                         if (security_vm_enough_memory(charged))
 163                                 return -ENOMEM;
 164                         newflags |= VM_ACCOUNT;
 165                 }
 166         }
 167
 168         /*
 169          * First try to merge with previous and/or next vma.
 170          */
 171         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 172         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 173                         vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 174         if (*pprev) {
 175                 vma = *pprev;
 176                 goto success;
 177         }
 178
 179         *pprev = vma;
 180
 181         if (start != vma->vm_start) {
 182                 error = split_vma(mm, vma, start, 1);
 183                 if (error)
 184                         goto fail;
 185         }
 186
 187         if (end != vma->vm_end) {
 188                 error = split_vma(mm, vma, end, 0);
 189                 if (error)
 190                         goto fail;
 191         }
 192
 193 success:
 194         /*
 195          * vm_flags and vm_page_prot are protected by the mmap_sem
 196          * held in write mode.
 197          */
 198         vma->vm_flags = newflags;
 199         vma->vm_page_prot = pgprot_modify(vma->vm_page_prot,
 200                                           vm_get_page_prot(newflags));
 201
 202         if (vma_wants_writenotify(vma)) {
 203                 vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
 204                 dirty_accountable = 1;
 205         }
 206
 207         mmu_notifier_invalidate_range_start(mm, start, end);
 208         if (is_vm_hugetlb_page(vma))
 209                 hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
 210         else
 211                 change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
 212         mmu_notifier_invalidate_range_end(mm, start, end);
 213         vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 214         vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 215         return 0;
 216
 217 fail:
 218         vm_unacct_memory(charged);
 219         return error;
 220 }
 221
 222 SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 223                 unsigned long, prot)
 224 {
 225         unsigned long vm_flags, nstart, end, tmp, reqprot;
 226         struct vm_area_struct *vma, *prev;
 227         int error = -EINVAL;
 228         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 229         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 230         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 231                 return -EINVAL;
 232
 233         if (start & ~PAGE_MASK)
 234                 return -EINVAL;
 235         if (!len)
 236                 return 0;
 237         len = PAGE_ALIGN(len);
 238         end = start + len;
 239         if (end <= start)
 240                 return -ENOMEM;
 241         if (!arch_validate_prot(prot))
 242                 return -EINVAL;
 243
 244         reqprot = prot;
 245         /*
 246          * Does the application expect PROT_READ to imply PROT_EXEC:
 247          */
 248         if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
 249                 prot |= PROT_EXEC;
 250
 251         vm_flags = calc_vm_prot_bits(prot);
 252
 253         down_write(&current->mm->mmap_sem);
 254
 255         vma = find_vma_prev(current->mm, start, &prev);
 256         error = -ENOMEM;
 257         if (!vma)
 258                 goto out;
 259         if (unlikely(grows & PROT_GROWSDOWN)) {
 260                 if (vma->vm_start >= end)
 261                         goto out;
 262                 start = vma->vm_start;
 263                 error = -EINVAL;
 264                 if (!(vma->vm_flags & VM_GROWSDOWN))
 265                         goto out;
 266         }
 267         else {
 268                 if (vma->vm_start > start)
 269                         goto out;
 270                 if (unlikely(grows & PROT_GROWSUP)) {
 271                         end = vma->vm_end;
 272                         error = -EINVAL;
 273                         if (!(vma->vm_flags & VM_GROWSUP))
 274                                 goto out;
 275                 }
 276         }
 277         if (start > vma->vm_start)
 278                 prev = vma;
 279
 280         for (nstart = start ; ; ) {
 281                 unsigned long newflags;
 282
 283                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 284
 285                 newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 286
 287                 /* newflags >> 4 shift VM_MAY% in place of VM_% */
 288                 if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 289                         error = -EACCES;
 290                         goto out;
 291                 }
 292
 293                 error = security_file_mprotect(vma, reqprot, prot);
 294                 if (error)
 295                         goto out;
 296
 297                 tmp = vma->vm_end;
 298                 if (tmp > end)
 299                         tmp = end;
 300                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 301                 if (error)
 302                         goto out;
 303                 nstart = tmp;
 304
 305                 if (nstart < prev->vm_end)
 306                         nstart = prev->vm_end;
 307                 if (nstart >= end)
 308                         goto out;
 309
 310                 vma = prev->vm_next;
 311                 if (!vma || vma->vm_start != nstart) {
 312                         error = -ENOMEM;
 313                         goto out;
 314                 }
 315         }
 316 out:
 317         up_write(&current->mm->mmap_sem);
 318         return error;
 319 }