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@lxorguk.ukuu.org.uk>
   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/shm.h>
  14 #include <linux/mman.h>
  15 #include <linux/fs.h>
  16 #include <linux/highmem.h>
  17 #include <linux/security.h>
  18 #include <linux/mempolicy.h>
  19 #include <linux/personality.h>
  20 #include <linux/syscalls.h>
  21 #include <linux/swap.h>
  22 #include <linux/swapops.h>
  23 #include <linux/mmu_notifier.h>
  24 #include <linux/migrate.h>
  25 #include <linux/perf_event.h>
  26 #include <asm/uaccess.h>
  27 #include <asm/pgtable.h>
  28 #include <asm/cacheflush.h>
  29 #include <asm/tlbflush.h>
  30
  31 #ifndef pgprot_modify
  32 static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
  33 {
  34         return newprot;
  35 }
  36 #endif
  37
  38 static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
  39                 unsigned long addr, unsigned long end, pgprot_t newprot,
  40                 int dirty_accountable)
  41 {
  42         pte_t *pte, oldpte;
  43         spinlock_t *ptl;
  44
  45         pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
  46         arch_enter_lazy_mmu_mode();
  47         do {
  48                 oldpte = *pte;
  49                 if (pte_present(oldpte)) {
  50                         pte_t ptent;
  51
  52                         ptent = ptep_modify_prot_start(mm, addr, pte);
  53                         ptent = pte_modify(ptent, newprot);
  54
  55                         /*
  56                          * Avoid taking write faults for pages we know to be
  57                          * dirty.
  58                          */
  59                         if (dirty_accountable && pte_dirty(ptent))
  60                                 ptent = pte_mkwrite(ptent);
  61
  62                         ptep_modify_prot_commit(mm, addr, pte, ptent);
  63                 } else if (PAGE_MIGRATION && !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                 }
  76         } while (pte++, addr += PAGE_SIZE, addr != end);
  77         arch_leave_lazy_mmu_mode();
  78         pte_unmap_unlock(pte - 1, ptl);
  79 }
  80
  81 static inline void change_pmd_range(struct vm_area_struct *vma, pud_t *pud,
  82                 unsigned long addr, unsigned long end, pgprot_t newprot,
  83                 int dirty_accountable)
  84 {
  85         pmd_t *pmd;
  86         unsigned long next;
  87
  88         pmd = pmd_offset(pud, addr);
  89         do {
  90                 next = pmd_addr_end(addr, end);
  91                 split_huge_page_pmd(vma->vm_mm, pmd);
  92                 if (pmd_none_or_clear_bad(pmd))
  93                         continue;
  94                 change_pte_range(vma->vm_mm, pmd, addr, next, newprot,
  95                                  dirty_accountable);
  96         } while (pmd++, addr = next, addr != end);
  97 }
  98
  99 static inline void change_pud_range(struct vm_area_struct *vma, 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(vma, pud, addr, next, newprot,
 112                                  dirty_accountable);
 113         } while (pud++, addr = next, addr != end);
 114 }
 115
 116 static void change_protection(struct vm_area_struct *vma,
 117                 unsigned long addr, unsigned long end, pgprot_t newprot,
 118                 int dirty_accountable)
 119 {
 120         struct mm_struct *mm = vma->vm_mm;
 121         pgd_t *pgd;
 122         unsigned long next;
 123         unsigned long start = addr;
 124
 125         BUG_ON(addr >= end);
 126         pgd = pgd_offset(mm, addr);
 127         flush_cache_range(vma, addr, end);
 128         do {
 129                 next = pgd_addr_end(addr, end);
 130                 if (pgd_none_or_clear_bad(pgd))
 131                         continue;
 132                 change_pud_range(vma, pgd, addr, next, newprot,
 133                                  dirty_accountable);
 134         } while (pgd++, addr = next, addr != end);
 135         flush_tlb_range(vma, start, end);
 136 }
 137
 138 int
 139 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 140         unsigned long start, unsigned long end, unsigned long newflags)
 141 {
 142         struct mm_struct *mm = vma->vm_mm;
 143         unsigned long oldflags = vma->vm_flags;
 144         long nrpages = (end - start) >> PAGE_SHIFT;
 145         unsigned long charged = 0;
 146         pgoff_t pgoff;
 147         int error;
 148         int dirty_accountable = 0;
 149
 150         if (newflags == oldflags) {
 151                 *pprev = vma;
 152                 return 0;
 153         }
 154
 155         /*
 156          * If we make a private mapping writable we increase our commit;
 157          * but (without finer accounting) cannot reduce our commit if we
 158          * make it unwritable again. hugetlb mapping were accounted for
 159          * even if read-only so there is no need to account for them here
 160          */
 161         if (newflags & VM_WRITE) {
 162                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
 163                                                 VM_SHARED|VM_NORESERVE))) {
 164                         charged = nrpages;
 165                         if (security_vm_enough_memory(charged))
 166                                 return -ENOMEM;
 167                         newflags |= VM_ACCOUNT;
 168                 }
 169         }
 170
 171         /*
 172          * First try to merge with previous and/or next vma.
 173          */
 174         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 175         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 176                         vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 177         if (*pprev) {
 178                 vma = *pprev;
 179                 goto success;
 180         }
 181
 182         *pprev = vma;
 183
 184         if (start != vma->vm_start) {
 185                 error = split_vma(mm, vma, start, 1);
 186                 if (error)
 187                         goto fail;
 188         }
 189
 190         if (end != vma->vm_end) {
 191                 error = split_vma(mm, vma, end, 0);
 192                 if (error)
 193                         goto fail;
 194         }
 195
 196 success:
 197         /*
 198          * vm_flags and vm_page_prot are protected by the mmap_sem
 199          * held in write mode.
 200          */
 201         vma->vm_flags = newflags;
 202         vma->vm_page_prot = pgprot_modify(vma->vm_page_prot,
 203                                           vm_get_page_prot(newflags));
 204
 205         if (vma_wants_writenotify(vma)) {
 206                 vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
 207                 dirty_accountable = 1;
 208         }
 209
 210         mmu_notifier_invalidate_range_start(mm, start, end);
 211         if (is_vm_hugetlb_page(vma))
 212                 hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
 213         else
 214                 change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
 215         mmu_notifier_invalidate_range_end(mm, start, end);
 216         vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 217         vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 218         perf_event_mmap(vma);
 219         return 0;
 220
 221 fail:
 222         vm_unacct_memory(charged);
 223         return error;
 224 }
 225
 226 SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 227                 unsigned long, prot)
 228 {
 229         unsigned long vm_flags, nstart, end, tmp, reqprot;
 230         struct vm_area_struct *vma, *prev;
 231         int error = -EINVAL;
 232         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 233         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 234         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 235                 return -EINVAL;
 236
 237         if (start & ~PAGE_MASK)
 238                 return -EINVAL;
 239         if (!len)
 240                 return 0;
 241         len = PAGE_ALIGN(len);
 242         end = start + len;
 243         if (end <= start)
 244                 return -ENOMEM;
 245         if (!arch_validate_prot(prot))
 246                 return -EINVAL;
 247
 248         reqprot = prot;
 249         /*
 250          * Does the application expect PROT_READ to imply PROT_EXEC:
 251          */
 252         if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
 253                 prot |= PROT_EXEC;
 254
 255         vm_flags = calc_vm_prot_bits(prot);
 256
 257         down_write(&current->mm->mmap_sem);
 258
 259         vma = find_vma_prev(current->mm, start, &prev);
 260         error = -ENOMEM;
 261         if (!vma)
 262                 goto out;
 263         if (unlikely(grows & PROT_GROWSDOWN)) {
 264                 if (vma->vm_start >= end)
 265                         goto out;
 266                 start = vma->vm_start;
 267                 error = -EINVAL;
 268                 if (!(vma->vm_flags & VM_GROWSDOWN))
 269                         goto out;
 270         }
 271         else {
 272                 if (vma->vm_start > start)
 273                         goto out;
 274                 if (unlikely(grows & PROT_GROWSUP)) {
 275                         end = vma->vm_end;
 276                         error = -EINVAL;
 277                         if (!(vma->vm_flags & VM_GROWSUP))
 278                                 goto out;
 279                 }
 280         }
 281         if (start > vma->vm_start)
 282                 prev = vma;
 283
 284         for (nstart = start ; ; ) {
 285                 unsigned long newflags;
 286
 287                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 288
 289                 newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 290
 291                 /* newflags >> 4 shift VM_MAY% in place of VM_% */
 292                 if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 293                         error = -EACCES;
 294                         goto out;
 295                 }
 296
 297                 error = security_file_mprotect(vma, reqprot, prot);
 298                 if (error)
 299                         goto out;
 300
 301                 tmp = vma->vm_end;
 302                 if (tmp > end)
 303                         tmp = end;
 304                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 305                 if (error)
 306                         goto out;
 307                 nstart = tmp;
 308
 309                 if (nstart < prev->vm_end)
 310                         nstart = prev->vm_end;
 311                 if (nstart >= end)
 312                         goto out;
 313
 314                 vma = prev->vm_next;
 315                 if (!vma || vma->vm_start != nstart) {
 316                         error = -ENOMEM;
 317                         goto out;
 318                 }
 319         }
 320 out:
 321         up_write(&current->mm->mmap_sem);
 322         return error;
 323 }