mm/mprotect.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  mm/mprotect.c
   4  *
   5  *  (C) Copyright 1994 Linus Torvalds
   6  *  (C) Copyright 2002 Christoph Hellwig
   7  *
   8  *  Address space accounting code       <alan@lxorguk.ukuu.org.uk>
   9  *  (C) Copyright 2002 Red Hat Inc, All Rights Reserved
  10  */
  11
  12 #include <linux/mm.h>
  13 #include <linux/hugetlb.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 <linux/migrate.h>
  26 #include <linux/perf_event.h>
  27 #include <linux/pkeys.h>
  28 #include <linux/ksm.h>
  29 #include <linux/uaccess.h>
  30 #include <asm/pgtable.h>
  31 #include <asm/cacheflush.h>
  32 #include <asm/mmu_context.h>
  33 #include <asm/tlbflush.h>
  34
  35 #include "internal.h"
  36
  37 static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
  38                 unsigned long addr, unsigned long end, pgprot_t newprot,
  39                 int dirty_accountable, int prot_numa)
  40 {
  41         struct mm_struct *mm = vma->vm_mm;
  42         pte_t *pte, oldpte;
  43         spinlock_t *ptl;
  44         unsigned long pages = 0;
  45         int target_node = NUMA_NO_NODE;
  46
  47         /*
  48          * Can be called with only the mmap_sem for reading by
  49          * prot_numa so we must check the pmd isn't constantly
  50          * changing from under us from pmd_none to pmd_trans_huge
  51          * and/or the other way around.
  52          */
  53         if (pmd_trans_unstable(pmd))
  54                 return 0;
  55
  56         /*
  57          * The pmd points to a regular pte so the pmd can't change
  58          * from under us even if the mmap_sem is only hold for
  59          * reading.
  60          */
  61         pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
  62
  63         /* Get target node for single threaded private VMAs */
  64         if (prot_numa && !(vma->vm_flags & VM_SHARED) &&
  65             atomic_read(&vma->vm_mm->mm_users) == 1)
  66                 target_node = numa_node_id();
  67
  68         flush_tlb_batched_pending(vma->vm_mm);
  69         arch_enter_lazy_mmu_mode();
  70         do {
  71                 oldpte = *pte;
  72                 if (pte_present(oldpte)) {
  73                         pte_t ptent;
  74                         bool preserve_write = prot_numa && pte_write(oldpte);
  75
  76                         /*
  77                          * Avoid trapping faults against the zero or KSM
  78                          * pages. See similar comment in change_huge_pmd.
  79                          */
  80                         if (prot_numa) {
  81                                 struct page *page;
  82
  83                                 page = vm_normal_page(vma, addr, oldpte);
  84                                 if (!page || PageKsm(page))
  85                                         continue;
  86
  87                                 /* Avoid TLB flush if possible */
  88                                 if (pte_protnone(oldpte))
  89                                         continue;
  90
  91                                 /*
  92                                  * Don't mess with PTEs if page is already on the node
  93                                  * a single-threaded process is running on.
  94                                  */
  95                                 if (target_node == page_to_nid(page))
  96                                         continue;
  97                         }
  98
  99                         ptent = ptep_modify_prot_start(mm, addr, pte);
 100                         ptent = pte_modify(ptent, newprot);
 101                         if (preserve_write)
 102                                 ptent = pte_mk_savedwrite(ptent);
 103
 104                         /* Avoid taking write faults for known dirty pages */
 105                         if (dirty_accountable && pte_dirty(ptent) &&
 106                                         (pte_soft_dirty(ptent) ||
 107                                          !(vma->vm_flags & VM_SOFTDIRTY))) {
 108                                 ptent = pte_mkwrite(ptent);
 109                         }
 110                         ptep_modify_prot_commit(mm, addr, pte, ptent);
 111                         pages++;
 112                 } else if (IS_ENABLED(CONFIG_MIGRATION)) {
 113                         swp_entry_t entry = pte_to_swp_entry(oldpte);
 114
 115                         if (is_write_migration_entry(entry)) {
 116                                 pte_t newpte;
 117                                 /*
 118                                  * A protection check is difficult so
 119                                  * just be safe and disable write
 120                                  */
 121                                 make_migration_entry_read(&entry);
 122                                 newpte = swp_entry_to_pte(entry);
 123                                 if (pte_swp_soft_dirty(oldpte))
 124                                         newpte = pte_swp_mksoft_dirty(newpte);
 125                                 set_pte_at(mm, addr, pte, newpte);
 126
 127                                 pages++;
 128                         }
 129
 130                         if (is_write_device_private_entry(entry)) {
 131                                 pte_t newpte;
 132
 133                                 /*
 134                                  * We do not preserve soft-dirtiness. See
 135                                  * copy_one_pte() for explanation.
 136                                  */
 137                                 make_device_private_entry_read(&entry);
 138                                 newpte = swp_entry_to_pte(entry);
 139                                 set_pte_at(mm, addr, pte, newpte);
 140
 141                                 pages++;
 142                         }
 143                 }
 144         } while (pte++, addr += PAGE_SIZE, addr != end);
 145         arch_leave_lazy_mmu_mode();
 146         pte_unmap_unlock(pte - 1, ptl);
 147
 148         return pages;
 149 }
 150
 151 static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
 152                 pud_t *pud, unsigned long addr, unsigned long end,
 153                 pgprot_t newprot, int dirty_accountable, int prot_numa)
 154 {
 155         pmd_t *pmd;
 156         struct mm_struct *mm = vma->vm_mm;
 157         unsigned long next;
 158         unsigned long pages = 0;
 159         unsigned long nr_huge_updates = 0;
 160         unsigned long mni_start = 0;
 161
 162         pmd = pmd_offset(pud, addr);
 163         do {
 164                 unsigned long this_pages;
 165
 166                 next = pmd_addr_end(addr, end);
 167                 if (!is_swap_pmd(*pmd) && !pmd_trans_huge(*pmd) && !pmd_devmap(*pmd)
 168                                 && pmd_none_or_clear_bad(pmd))
 169                         goto next;
 170
 171                 /* invoke the mmu notifier if the pmd is populated */
 172                 if (!mni_start) {
 173                         mni_start = addr;
 174                         mmu_notifier_invalidate_range_start(mm, mni_start, end);
 175                 }
 176
 177                 if (is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
 178                         if (next - addr != HPAGE_PMD_SIZE) {
 179                                 __split_huge_pmd(vma, pmd, addr, false, NULL);
 180                         } else {
 181                                 int nr_ptes = change_huge_pmd(vma, pmd, addr,
 182                                                 newprot, prot_numa);
 183
 184                                 if (nr_ptes) {
 185                                         if (nr_ptes == HPAGE_PMD_NR) {
 186                                                 pages += HPAGE_PMD_NR;
 187                                                 nr_huge_updates++;
 188                                         }
 189
 190                                         /* huge pmd was handled */
 191                                         goto next;
 192                                 }
 193                         }
 194                         /* fall through, the trans huge pmd just split */
 195                 }
 196                 this_pages = change_pte_range(vma, pmd, addr, next, newprot,
 197                                  dirty_accountable, prot_numa);
 198                 pages += this_pages;
 199 next:
 200                 cond_resched();
 201         } while (pmd++, addr = next, addr != end);
 202
 203         if (mni_start)
 204                 mmu_notifier_invalidate_range_end(mm, mni_start, end);
 205
 206         if (nr_huge_updates)
 207                 count_vm_numa_events(NUMA_HUGE_PTE_UPDATES, nr_huge_updates);
 208         return pages;
 209 }
 210
 211 static inline unsigned long change_pud_range(struct vm_area_struct *vma,
 212                 p4d_t *p4d, unsigned long addr, unsigned long end,
 213                 pgprot_t newprot, int dirty_accountable, int prot_numa)
 214 {
 215         pud_t *pud;
 216         unsigned long next;
 217         unsigned long pages = 0;
 218
 219         pud = pud_offset(p4d, addr);
 220         do {
 221                 next = pud_addr_end(addr, end);
 222                 if (pud_none_or_clear_bad(pud))
 223                         continue;
 224                 pages += change_pmd_range(vma, pud, addr, next, newprot,
 225                                  dirty_accountable, prot_numa);
 226         } while (pud++, addr = next, addr != end);
 227
 228         return pages;
 229 }
 230
 231 static inline unsigned long change_p4d_range(struct vm_area_struct *vma,
 232                 pgd_t *pgd, unsigned long addr, unsigned long end,
 233                 pgprot_t newprot, int dirty_accountable, int prot_numa)
 234 {
 235         p4d_t *p4d;
 236         unsigned long next;
 237         unsigned long pages = 0;
 238
 239         p4d = p4d_offset(pgd, addr);
 240         do {
 241                 next = p4d_addr_end(addr, end);
 242                 if (p4d_none_or_clear_bad(p4d))
 243                         continue;
 244                 pages += change_pud_range(vma, p4d, addr, next, newprot,
 245                                  dirty_accountable, prot_numa);
 246         } while (p4d++, addr = next, addr != end);
 247
 248         return pages;
 249 }
 250
 251 static unsigned long change_protection_range(struct vm_area_struct *vma,
 252                 unsigned long addr, unsigned long end, pgprot_t newprot,
 253                 int dirty_accountable, int prot_numa)
 254 {
 255         struct mm_struct *mm = vma->vm_mm;
 256         pgd_t *pgd;
 257         unsigned long next;
 258         unsigned long start = addr;
 259         unsigned long pages = 0;
 260
 261         BUG_ON(addr >= end);
 262         pgd = pgd_offset(mm, addr);
 263         flush_cache_range(vma, addr, end);
 264         inc_tlb_flush_pending(mm);
 265         do {
 266                 next = pgd_addr_end(addr, end);
 267                 if (pgd_none_or_clear_bad(pgd))
 268                         continue;
 269                 pages += change_p4d_range(vma, pgd, addr, next, newprot,
 270                                  dirty_accountable, prot_numa);
 271         } while (pgd++, addr = next, addr != end);
 272
 273         /* Only flush the TLB if we actually modified any entries: */
 274         if (pages)
 275                 flush_tlb_range(vma, start, end);
 276         dec_tlb_flush_pending(mm);
 277
 278         return pages;
 279 }
 280
 281 unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
 282                        unsigned long end, pgprot_t newprot,
 283                        int dirty_accountable, int prot_numa)
 284 {
 285         unsigned long pages;
 286
 287         if (is_vm_hugetlb_page(vma))
 288                 pages = hugetlb_change_protection(vma, start, end, newprot);
 289         else
 290                 pages = change_protection_range(vma, start, end, newprot, dirty_accountable, prot_numa);
 291
 292         return pages;
 293 }
 294
 295 static int prot_none_pte_entry(pte_t *pte, unsigned long addr,
 296                                unsigned long next, struct mm_walk *walk)
 297 {
 298         return pfn_modify_allowed(pte_pfn(*pte), *(pgprot_t *)(walk->private)) ?
 299                 0 : -EACCES;
 300 }
 301
 302 static int prot_none_hugetlb_entry(pte_t *pte, unsigned long hmask,
 303                                    unsigned long addr, unsigned long next,
 304                                    struct mm_walk *walk)
 305 {
 306         return pfn_modify_allowed(pte_pfn(*pte), *(pgprot_t *)(walk->private)) ?
 307                 0 : -EACCES;
 308 }
 309
 310 static int prot_none_test(unsigned long addr, unsigned long next,
 311                           struct mm_walk *walk)
 312 {
 313         return 0;
 314 }
 315
 316 static int prot_none_walk(struct vm_area_struct *vma, unsigned long start,
 317                            unsigned long end, unsigned long newflags)
 318 {
 319         pgprot_t new_pgprot = vm_get_page_prot(newflags);
 320         struct mm_walk prot_none_walk = {
 321                 .pte_entry = prot_none_pte_entry,
 322                 .hugetlb_entry = prot_none_hugetlb_entry,
 323                 .test_walk = prot_none_test,
 324                 .mm = current->mm,
 325                 .private = &new_pgprot,
 326         };
 327
 328         return walk_page_range(start, end, &prot_none_walk);
 329 }
 330
 331 int
 332 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 333         unsigned long start, unsigned long end, unsigned long newflags)
 334 {
 335         struct mm_struct *mm = vma->vm_mm;
 336         unsigned long oldflags = vma->vm_flags;
 337         long nrpages = (end - start) >> PAGE_SHIFT;
 338         unsigned long charged = 0;
 339         pgoff_t pgoff;
 340         int error;
 341         int dirty_accountable = 0;
 342
 343         if (newflags == oldflags) {
 344                 *pprev = vma;
 345                 return 0;
 346         }
 347
 348         /*
 349          * Do PROT_NONE PFN permission checks here when we can still
 350          * bail out without undoing a lot of state. This is a rather
 351          * uncommon case, so doesn't need to be very optimized.
 352          */
 353         if (arch_has_pfn_modify_check() &&
 354             (vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) &&
 355             (newflags & (VM_READ|VM_WRITE|VM_EXEC)) == 0) {
 356                 error = prot_none_walk(vma, start, end, newflags);
 357                 if (error)
 358                         return error;
 359         }
 360
 361         /*
 362          * If we make a private mapping writable we increase our commit;
 363          * but (without finer accounting) cannot reduce our commit if we
 364          * make it unwritable again. hugetlb mapping were accounted for
 365          * even if read-only so there is no need to account for them here
 366          */
 367         if (newflags & VM_WRITE) {
 368                 /* Check space limits when area turns into data. */
 369                 if (!may_expand_vm(mm, newflags, nrpages) &&
 370                                 may_expand_vm(mm, oldflags, nrpages))
 371                         return -ENOMEM;
 372                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
 373                                                 VM_SHARED|VM_NORESERVE))) {
 374                         charged = nrpages;
 375                         if (security_vm_enough_memory_mm(mm, charged))
 376                                 return -ENOMEM;
 377                         newflags |= VM_ACCOUNT;
 378                 }
 379         }
 380
 381         /*
 382          * First try to merge with previous and/or next vma.
 383          */
 384         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 385         *pprev = vma_merge(mm, *pprev, start, end, newflags,
 386                            vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
 387                            vma->vm_userfaultfd_ctx, vma_get_anon_name(vma));
 388         if (*pprev) {
 389                 vma = *pprev;
 390                 VM_WARN_ON((vma->vm_flags ^ newflags) & ~VM_SOFTDIRTY);
 391                 goto success;
 392         }
 393
 394         *pprev = vma;
 395
 396         if (start != vma->vm_start) {
 397                 error = split_vma(mm, vma, start, 1);
 398                 if (error)
 399                         goto fail;
 400         }
 401
 402         if (end != vma->vm_end) {
 403                 error = split_vma(mm, vma, end, 0);
 404                 if (error)
 405                         goto fail;
 406         }
 407
 408 success:
 409         /*
 410          * vm_flags and vm_page_prot are protected by the mmap_sem
 411          * held in write mode.
 412          */
 413         vma->vm_flags = newflags;
 414         dirty_accountable = vma_wants_writenotify(vma, vma->vm_page_prot);
 415         vma_set_page_prot(vma);
 416
 417         change_protection(vma, start, end, vma->vm_page_prot,
 418                           dirty_accountable, 0);
 419
 420         /*
 421          * Private VM_LOCKED VMA becoming writable: trigger COW to avoid major
 422          * fault on access.
 423          */
 424         if ((oldflags & (VM_WRITE | VM_SHARED | VM_LOCKED)) == VM_LOCKED &&
 425                         (newflags & VM_WRITE)) {
 426                 populate_vma_page_range(vma, start, end, NULL);
 427         }
 428
 429         vm_stat_account(mm, oldflags, -nrpages);
 430         vm_stat_account(mm, newflags, nrpages);
 431         perf_event_mmap(vma);
 432         return 0;
 433
 434 fail:
 435         vm_unacct_memory(charged);
 436         return error;
 437 }
 438
 439 /*
 440  * pkey==-1 when doing a legacy mprotect()
 441  */
 442 static int do_mprotect_pkey(unsigned long start, size_t len,
 443                 unsigned long prot, int pkey)
 444 {
 445         unsigned long nstart, end, tmp, reqprot;
 446         struct vm_area_struct *vma, *prev;
 447         int error = -EINVAL;
 448         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 449         const bool rier = (current->personality & READ_IMPLIES_EXEC) &&
 450                                 (prot & PROT_READ);
 451
 452         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 453         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 454                 return -EINVAL;
 455
 456         if (start & ~PAGE_MASK)
 457                 return -EINVAL;
 458         if (!len)
 459                 return 0;
 460         len = PAGE_ALIGN(len);
 461         end = start + len;
 462         if (end <= start)
 463                 return -ENOMEM;
 464         if (!arch_validate_prot(prot))
 465                 return -EINVAL;
 466
 467         reqprot = prot;
 468
 469         if (down_write_killable(&current->mm->mmap_sem))
 470                 return -EINTR;
 471
 472         /*
 473          * If userspace did not allocate the pkey, do not let
 474          * them use it here.
 475          */
 476         error = -EINVAL;
 477         if ((pkey != -1) && !mm_pkey_is_allocated(current->mm, pkey))
 478                 goto out;
 479
 480         vma = find_vma(current->mm, start);
 481         error = -ENOMEM;
 482         if (!vma)
 483                 goto out;
 484         prev = vma->vm_prev;
 485         if (unlikely(grows & PROT_GROWSDOWN)) {
 486                 if (vma->vm_start >= end)
 487                         goto out;
 488                 start = vma->vm_start;
 489                 error = -EINVAL;
 490                 if (!(vma->vm_flags & VM_GROWSDOWN))
 491                         goto out;
 492         } else {
 493                 if (vma->vm_start > start)
 494                         goto out;
 495                 if (unlikely(grows & PROT_GROWSUP)) {
 496                         end = vma->vm_end;
 497                         error = -EINVAL;
 498                         if (!(vma->vm_flags & VM_GROWSUP))
 499                                 goto out;
 500                 }
 501         }
 502         if (start > vma->vm_start)
 503                 prev = vma;
 504
 505         for (nstart = start ; ; ) {
 506                 unsigned long mask_off_old_flags;
 507                 unsigned long newflags;
 508                 int new_vma_pkey;
 509
 510                 /* Here we know that vma->vm_start <= nstart < vma->vm_end. */
 511
 512                 /* Does the application expect PROT_READ to imply PROT_EXEC */
 513                 if (rier && (vma->vm_flags & VM_MAYEXEC))
 514                         prot |= PROT_EXEC;
 515
 516                 /*
 517                  * Each mprotect() call explicitly passes r/w/x permissions.
 518                  * If a permission is not passed to mprotect(), it must be
 519                  * cleared from the VMA.
 520                  */
 521                 mask_off_old_flags = VM_READ | VM_WRITE | VM_EXEC |
 522                                         ARCH_VM_PKEY_FLAGS;
 523
 524                 new_vma_pkey = arch_override_mprotect_pkey(vma, prot, pkey);
 525                 newflags = calc_vm_prot_bits(prot, new_vma_pkey);
 526                 newflags |= (vma->vm_flags & ~mask_off_old_flags);
 527
 528                 /* newflags >> 4 shift VM_MAY% in place of VM_% */
 529                 if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 530                         error = -EACCES;
 531                         goto out;
 532                 }
 533
 534                 error = security_file_mprotect(vma, reqprot, prot);
 535                 if (error)
 536                         goto out;
 537
 538                 tmp = vma->vm_end;
 539                 if (tmp > end)
 540                         tmp = end;
 541                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 542                 if (error)
 543                         goto out;
 544                 nstart = tmp;
 545
 546                 if (nstart < prev->vm_end)
 547                         nstart = prev->vm_end;
 548                 if (nstart >= end)
 549                         goto out;
 550
 551                 vma = prev->vm_next;
 552                 if (!vma || vma->vm_start != nstart) {
 553                         error = -ENOMEM;
 554                         goto out;
 555                 }
 556                 prot = reqprot;
 557         }
 558 out:
 559         up_write(&current->mm->mmap_sem);
 560         return error;
 561 }
 562
 563 SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 564                 unsigned long, prot)
 565 {
 566         return do_mprotect_pkey(start, len, prot, -1);
 567 }
 568
 569 #ifdef CONFIG_ARCH_HAS_PKEYS
 570
 571 SYSCALL_DEFINE4(pkey_mprotect, unsigned long, start, size_t, len,
 572                 unsigned long, prot, int, pkey)
 573 {
 574         return do_mprotect_pkey(start, len, prot, pkey);
 575 }
 576
 577 SYSCALL_DEFINE2(pkey_alloc, unsigned long, flags, unsigned long, init_val)
 578 {
 579         int pkey;
 580         int ret;
 581
 582         /* No flags supported yet. */
 583         if (flags)
 584                 return -EINVAL;
 585         /* check for unsupported init values */
 586         if (init_val & ~PKEY_ACCESS_MASK)
 587                 return -EINVAL;
 588
 589         down_write(&current->mm->mmap_sem);
 590         pkey = mm_pkey_alloc(current->mm);
 591
 592         ret = -ENOSPC;
 593         if (pkey == -1)
 594                 goto out;
 595
 596         ret = arch_set_user_pkey_access(current, pkey, init_val);
 597         if (ret) {
 598                 mm_pkey_free(current->mm, pkey);
 599                 goto out;
 600         }
 601         ret = pkey;
 602 out:
 603         up_write(&current->mm->mmap_sem);
 604         return ret;
 605 }
 606
 607 SYSCALL_DEFINE1(pkey_free, int, pkey)
 608 {
 609         int ret;
 610
 611         down_write(&current->mm->mmap_sem);
 612         ret = mm_pkey_free(current->mm, pkey);
 613         up_write(&current->mm->mmap_sem);
 614
 615         /*
 616          * We could provie warnings or errors if any VMA still
 617          * has the pkey set here.
 618          */
 619         return ret;
 620 }
 621
 622 #endif /* CONFIG_ARCH_HAS_PKEYS */