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