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 unsigned long 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         unsigned long pages = 0;
  45
  46         pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
  47         arch_enter_lazy_mmu_mode();
  48         do {
  49                 oldpte = *pte;
  50                 if (pte_present(oldpte)) {
  51                         pte_t ptent;
  52
  53                         ptent = ptep_modify_prot_start(mm, addr, pte);
  54                         ptent = pte_modify(ptent, newprot);
  55
  56                         /*
  57                          * Avoid taking write faults for pages we know to be
  58                          * dirty.
  59                          */
  60                         if (dirty_accountable && pte_dirty(ptent))
  61                                 ptent = pte_mkwrite(ptent);
  62
  63                         ptep_modify_prot_commit(mm, addr, pte, ptent);
  64                         pages++;
  65                 } else if (IS_ENABLED(CONFIG_MIGRATION) && !pte_file(oldpte)) {
  66                         swp_entry_t entry = pte_to_swp_entry(oldpte);
  67
  68                         if (is_write_migration_entry(entry)) {
  69                                 /*
  70                                  * A protection check is difficult so
  71                                  * just be safe and disable write
  72                                  */
  73                                 make_migration_entry_read(&entry);
  74                                 set_pte_at(mm, addr, pte,
  75                                         swp_entry_to_pte(entry));
  76                         }
  77                         pages++;
  78                 }
  79         } while (pte++, addr += PAGE_SIZE, addr != end);
  80         arch_leave_lazy_mmu_mode();
  81         pte_unmap_unlock(pte - 1, ptl);
  82
  83         return pages;
  84 }
  85
  86 static inline unsigned long change_pmd_range(struct vm_area_struct *vma, pud_t *pud,
  87                 unsigned long addr, unsigned long end, pgprot_t newprot,
  88                 int dirty_accountable)
  89 {
  90         pmd_t *pmd;
  91         unsigned long next;
  92         unsigned long pages = 0;
  93
  94         pmd = pmd_offset(pud, addr);
  95         do {
  96                 next = pmd_addr_end(addr, end);
  97                 if (pmd_trans_huge(*pmd)) {
  98                         if (next - addr != HPAGE_PMD_SIZE)
  99                                 split_huge_page_pmd(vma->vm_mm, pmd);
 100                         else if (change_huge_pmd(vma, pmd, addr, newprot)) {
 101                                 pages += HPAGE_PMD_NR;
 102                                 continue;
 103                         }
 104                         /* fall through */
 105                 }
 106                 if (pmd_none_or_clear_bad(pmd))
 107                         continue;
 108                 pages += change_pte_range(vma->vm_mm, pmd, addr, next, newprot,
 109                                  dirty_accountable);
 110         } while (pmd++, addr = next, addr != end);
 111
 112         return pages;
 113 }
 114
 115 static inline unsigned long change_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
 116                 unsigned long addr, unsigned long end, pgprot_t newprot,
 117                 int dirty_accountable)
 118 {
 119         pud_t *pud;
 120         unsigned long next;
 121         unsigned long pages = 0;
 122
 123         pud = pud_offset(pgd, addr);
 124         do {
 125                 next = pud_addr_end(addr, end);
 126                 if (pud_none_or_clear_bad(pud))
 127                         continue;
 128                 pages += change_pmd_range(vma, pud, addr, next, newprot,
 129                                  dirty_accountable);
 130         } while (pud++, addr = next, addr != end);
 131
 132         return pages;
 133 }
 134
 135 static unsigned long change_protection_range(struct vm_area_struct *vma,
 136                 unsigned long addr, unsigned long end, pgprot_t newprot,
 137                 int dirty_accountable)
 138 {
 139         struct mm_struct *mm = vma->vm_mm;
 140         pgd_t *pgd;
 141         unsigned long next;
 142         unsigned long start = addr;
 143         unsigned long pages = 0;
 144
 145         BUG_ON(addr >= end);
 146         pgd = pgd_offset(mm, addr);
 147         flush_cache_range(vma, addr, end);
 148         do {
 149                 next = pgd_addr_end(addr, end);
 150                 if (pgd_none_or_clear_bad(pgd))
 151                         continue;
 152                 pages += change_pud_range(vma, pgd, addr, next, newprot,
 153                                  dirty_accountable);
 154         } while (pgd++, addr = next, addr != end);
 155
 156         flush_tlb_range(vma, start, end);
 157
 158         return pages;
 159 }
 160
 161 unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
 162                        unsigned long end, pgprot_t newprot,
 163                        int dirty_accountable)
 164 {
 165         struct mm_struct *mm = vma->vm_mm;
 166         unsigned long pages;
 167
 168         mmu_notifier_invalidate_range_start(mm, start, end);
 169         if (is_vm_hugetlb_page(vma))
 170                 pages = hugetlb_change_protection(vma, start, end, newprot);
 171         else
 172                 pages = change_protection_range(vma, start, end, newprot, dirty_accountable);
 173         mmu_notifier_invalidate_range_end(mm, start, end);
 174
 175         return pages;
 176 }
 177
 178 int
 179 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 180         unsigned long start, unsigned long end, unsigned long newflags)
 181 {
 182         struct mm_struct *mm = vma->vm_mm;
 183         unsigned long oldflags = vma->vm_flags;
 184         long nrpages = (end - start) >> PAGE_SHIFT;
 185         unsigned long charged = 0;
 186         pgoff_t pgoff;
 187         int error;
 188         int dirty_accountable = 0;
 189
 190         if (newflags == oldflags) {
 191                 *pprev = vma;
 192                 return 0;
 193         }
 194
 195         /*
 196          * If we make a private mapping writable we increase our commit;
 197          * but (without finer accounting) cannot reduce our commit if we
 198          * make it unwritable again. hugetlb mapping were accounted for
 199          * even if read-only so there is no need to account for them here
 200          */
 201         if (newflags & VM_WRITE) {
 202                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
 203                                                 VM_SHARED|VM_NORESERVE))) {
 204                         charged = nrpages;
 205                         if (security_vm_enough_memory_mm(mm, charged))
 206                                 return -ENOMEM;
 207                         newflags |= VM_ACCOUNT;
 208                 }
 209         }
 210
 211         /*
 212          * First try to merge with previous and/or next vma.
 213          */
 214         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 215         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 216                         vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 217         if (*pprev) {
 218                 vma = *pprev;
 219                 goto success;
 220         }
 221
 222         *pprev = vma;
 223
 224         if (start != vma->vm_start) {
 225                 error = split_vma(mm, vma, start, 1);
 226                 if (error)
 227                         goto fail;
 228         }
 229
 230         if (end != vma->vm_end) {
 231                 error = split_vma(mm, vma, end, 0);
 232                 if (error)
 233                         goto fail;
 234         }
 235
 236 success:
 237         /*
 238          * vm_flags and vm_page_prot are protected by the mmap_sem
 239          * held in write mode.
 240          */
 241         vma->vm_flags = newflags;
 242         vma->vm_page_prot = pgprot_modify(vma->vm_page_prot,
 243                                           vm_get_page_prot(newflags));
 244
 245         if (vma_wants_writenotify(vma)) {
 246                 vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
 247                 dirty_accountable = 1;
 248         }
 249
 250         change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
 251
 252         vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 253         vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 254         perf_event_mmap(vma);
 255         return 0;
 256
 257 fail:
 258         vm_unacct_memory(charged);
 259         return error;
 260 }
 261
 262 SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 263                 unsigned long, prot)
 264 {
 265         unsigned long vm_flags, nstart, end, tmp, reqprot;
 266         struct vm_area_struct *vma, *prev;
 267         int error = -EINVAL;
 268         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 269         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 270         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 271                 return -EINVAL;
 272
 273         if (start & ~PAGE_MASK)
 274                 return -EINVAL;
 275         if (!len)
 276                 return 0;
 277         len = PAGE_ALIGN(len);
 278         end = start + len;
 279         if (end <= start)
 280                 return -ENOMEM;
 281         if (!arch_validate_prot(prot))
 282                 return -EINVAL;
 283
 284         reqprot = prot;
 285         /*
 286          * Does the application expect PROT_READ to imply PROT_EXEC:
 287          */
 288         if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
 289                 prot |= PROT_EXEC;
 290
 291         vm_flags = calc_vm_prot_bits(prot);
 292
 293         down_write(&current->mm->mmap_sem);
 294
 295         vma = find_vma(current->mm, start);
 296         error = -ENOMEM;
 297         if (!vma)
 298                 goto out;
 299         prev = vma->vm_prev;
 300         if (unlikely(grows & PROT_GROWSDOWN)) {
 301                 if (vma->vm_start >= end)
 302                         goto out;
 303                 start = vma->vm_start;
 304                 error = -EINVAL;
 305                 if (!(vma->vm_flags & VM_GROWSDOWN))
 306                         goto out;
 307         }
 308         else {
 309                 if (vma->vm_start > start)
 310                         goto out;
 311                 if (unlikely(grows & PROT_GROWSUP)) {
 312                         end = vma->vm_end;
 313                         error = -EINVAL;
 314                         if (!(vma->vm_flags & VM_GROWSUP))
 315                                 goto out;
 316                 }
 317         }
 318         if (start > vma->vm_start)
 319                 prev = vma;
 320
 321         for (nstart = start ; ; ) {
 322                 unsigned long newflags;
 323
 324                 /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 325
 326                 newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 327
 328                 /* newflags >> 4 shift VM_MAY% in place of VM_% */
 329                 if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 330                         error = -EACCES;
 331                         goto out;
 332                 }
 333
 334                 error = security_file_mprotect(vma, reqprot, prot);
 335                 if (error)
 336                         goto out;
 337
 338                 tmp = vma->vm_end;
 339                 if (tmp > end)
 340                         tmp = end;
 341                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 342                 if (error)
 343                         goto out;
 344                 nstart = tmp;
 345
 346                 if (nstart < prev->vm_end)
 347                         nstart = prev->vm_end;
 348                 if (nstart >= end)
 349                         goto out;
 350
 351                 vma = prev->vm_next;
 352                 if (!vma || vma->vm_start != nstart) {
 353                         error = -ENOMEM;
 354                         goto out;
 355                 }
 356         }
 357 out:
 358         up_write(&current->mm->mmap_sem);
 359         return error;
 360 }