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/pagewalk.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 <linux/mm_inline.h>
  31 #include <linux/pgtable.h>
  32 #include <linux/sched/sysctl.h>
  33 #include <linux/userfaultfd_k.h>
  34 #include <linux/memory-tiers.h>
  35 #include <uapi/linux/mman.h>
  36 #include <asm/cacheflush.h>
  37 #include <asm/mmu_context.h>
  38 #include <asm/tlbflush.h>
  39 #include <asm/tlb.h>
  40
  41 #include "internal.h"
  42
  43 bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr,
  44                              pte_t pte)
  45 {
  46         struct page *page;
  47
  48         if (WARN_ON_ONCE(!(vma->vm_flags & VM_WRITE)))
  49                 return false;
  50
  51         /* Don't touch entries that are not even readable. */
  52         if (pte_protnone(pte))
  53                 return false;
  54
  55         /* Do we need write faults for softdirty tracking? */
  56         if (pte_needs_soft_dirty_wp(vma, pte))
  57                 return false;
  58
  59         /* Do we need write faults for uffd-wp tracking? */
  60         if (userfaultfd_pte_wp(vma, pte))
  61                 return false;
  62
  63         if (!(vma->vm_flags & VM_SHARED)) {
  64                 /*
  65                  * Writable MAP_PRIVATE mapping: We can only special-case on
  66                  * exclusive anonymous pages, because we know that our
  67                  * write-fault handler similarly would map them writable without
  68                  * any additional checks while holding the PT lock.
  69                  */
  70                 page = vm_normal_page(vma, addr, pte);
  71                 return page && PageAnon(page) && PageAnonExclusive(page);
  72         }
  73
  74         VM_WARN_ON_ONCE(is_zero_pfn(pte_pfn(pte)) && pte_dirty(pte));
  75
  76         /*
  77          * Writable MAP_SHARED mapping: "clean" might indicate that the FS still
  78          * needs a real write-fault for writenotify
  79          * (see vma_wants_writenotify()). If "dirty", the assumption is that the
  80          * FS was already notified and we can simply mark the PTE writable
  81          * just like the write-fault handler would do.
  82          */
  83         return pte_dirty(pte);
  84 }
  85
  86 static long change_pte_range(struct mmu_gather *tlb,
  87                 struct vm_area_struct *vma, pmd_t *pmd, unsigned long addr,
  88                 unsigned long end, pgprot_t newprot, unsigned long cp_flags)
  89 {
  90         pte_t *pte, oldpte;
  91         spinlock_t *ptl;
  92         long pages = 0;
  93         int target_node = NUMA_NO_NODE;
  94         bool prot_numa = cp_flags & MM_CP_PROT_NUMA;
  95         bool uffd_wp = cp_flags & MM_CP_UFFD_WP;
  96         bool uffd_wp_resolve = cp_flags & MM_CP_UFFD_WP_RESOLVE;
  97
  98         tlb_change_page_size(tlb, PAGE_SIZE);
  99         pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
 100         if (!pte)
 101                 return -EAGAIN;
 102
 103         /* Get target node for single threaded private VMAs */
 104         if (prot_numa && !(vma->vm_flags & VM_SHARED) &&
 105             atomic_read(&vma->vm_mm->mm_users) == 1)
 106                 target_node = numa_node_id();
 107
 108         flush_tlb_batched_pending(vma->vm_mm);
 109         arch_enter_lazy_mmu_mode();
 110         do {
 111                 oldpte = ptep_get(pte);
 112                 if (pte_present(oldpte)) {
 113                         pte_t ptent;
 114
 115                         /*
 116                          * Avoid trapping faults against the zero or KSM
 117                          * pages. See similar comment in change_huge_pmd.
 118                          */
 119                         if (prot_numa) {
 120                                 struct folio *folio;
 121                                 int nid;
 122                                 bool toptier;
 123
 124                                 /* Avoid TLB flush if possible */
 125                                 if (pte_protnone(oldpte))
 126                                         continue;
 127
 128                                 folio = vm_normal_folio(vma, addr, oldpte);
 129                                 if (!folio || folio_is_zone_device(folio) ||
 130                                     folio_test_ksm(folio))
 131                                         continue;
 132
 133                                 /* Also skip shared copy-on-write pages */
 134                                 if (is_cow_mapping(vma->vm_flags) &&
 135                                     (folio_maybe_dma_pinned(folio) ||
 136                                      folio_likely_mapped_shared(folio)))
 137                                         continue;
 138
 139                                 /*
 140                                  * While migration can move some dirty pages,
 141                                  * it cannot move them all from MIGRATE_ASYNC
 142                                  * context.
 143                                  */
 144                                 if (folio_is_file_lru(folio) &&
 145                                     folio_test_dirty(folio))
 146                                         continue;
 147
 148                                 /*
 149                                  * Don't mess with PTEs if page is already on the node
 150                                  * a single-threaded process is running on.
 151                                  */
 152                                 nid = folio_nid(folio);
 153                                 if (target_node == nid)
 154                                         continue;
 155                                 toptier = node_is_toptier(nid);
 156
 157                                 /*
 158                                  * Skip scanning top tier node if normal numa
 159                                  * balancing is disabled
 160                                  */
 161                                 if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_NORMAL) &&
 162                                     toptier)
 163                                         continue;
 164                                 if (folio_use_access_time(folio))
 165                                         folio_xchg_access_time(folio,
 166                                                 jiffies_to_msecs(jiffies));
 167                         }
 168
 169                         oldpte = ptep_modify_prot_start(vma, addr, pte);
 170                         ptent = pte_modify(oldpte, newprot);
 171
 172                         if (uffd_wp)
 173                                 ptent = pte_mkuffd_wp(ptent);
 174                         else if (uffd_wp_resolve)
 175                                 ptent = pte_clear_uffd_wp(ptent);
 176
 177                         /*
 178                          * In some writable, shared mappings, we might want
 179                          * to catch actual write access -- see
 180                          * vma_wants_writenotify().
 181                          *
 182                          * In all writable, private mappings, we have to
 183                          * properly handle COW.
 184                          *
 185                          * In both cases, we can sometimes still change PTEs
 186                          * writable and avoid the write-fault handler, for
 187                          * example, if a PTE is already dirty and no other
 188                          * COW or special handling is required.
 189                          */
 190                         if ((cp_flags & MM_CP_TRY_CHANGE_WRITABLE) &&
 191                             !pte_write(ptent) &&
 192                             can_change_pte_writable(vma, addr, ptent))
 193                                 ptent = pte_mkwrite(ptent, vma);
 194
 195                         ptep_modify_prot_commit(vma, addr, pte, oldpte, ptent);
 196                         if (pte_needs_flush(oldpte, ptent))
 197                                 tlb_flush_pte_range(tlb, addr, PAGE_SIZE);
 198                         pages++;
 199                 } else if (is_swap_pte(oldpte)) {
 200                         swp_entry_t entry = pte_to_swp_entry(oldpte);
 201                         pte_t newpte;
 202
 203                         if (is_writable_migration_entry(entry)) {
 204                                 struct folio *folio = pfn_swap_entry_folio(entry);
 205
 206                                 /*
 207                                  * A protection check is difficult so
 208                                  * just be safe and disable write
 209                                  */
 210                                 if (folio_test_anon(folio))
 211                                         entry = make_readable_exclusive_migration_entry(
 212                                                              swp_offset(entry));
 213                                 else
 214                                         entry = make_readable_migration_entry(swp_offset(entry));
 215                                 newpte = swp_entry_to_pte(entry);
 216                                 if (pte_swp_soft_dirty(oldpte))
 217                                         newpte = pte_swp_mksoft_dirty(newpte);
 218                         } else if (is_writable_device_private_entry(entry)) {
 219                                 /*
 220                                  * We do not preserve soft-dirtiness. See
 221                                  * copy_nonpresent_pte() for explanation.
 222                                  */
 223                                 entry = make_readable_device_private_entry(
 224                                                         swp_offset(entry));
 225                                 newpte = swp_entry_to_pte(entry);
 226                                 if (pte_swp_uffd_wp(oldpte))
 227                                         newpte = pte_swp_mkuffd_wp(newpte);
 228                         } else if (is_writable_device_exclusive_entry(entry)) {
 229                                 entry = make_readable_device_exclusive_entry(
 230                                                         swp_offset(entry));
 231                                 newpte = swp_entry_to_pte(entry);
 232                                 if (pte_swp_soft_dirty(oldpte))
 233                                         newpte = pte_swp_mksoft_dirty(newpte);
 234                                 if (pte_swp_uffd_wp(oldpte))
 235                                         newpte = pte_swp_mkuffd_wp(newpte);
 236                         } else if (is_pte_marker_entry(entry)) {
 237                                 /*
 238                                  * Ignore error swap entries unconditionally,
 239                                  * because any access should sigbus/sigsegv
 240                                  * anyway.
 241                                  */
 242                                 if (is_poisoned_swp_entry(entry) ||
 243                                     is_guard_swp_entry(entry))
 244                                         continue;
 245                                 /*
 246                                  * If this is uffd-wp pte marker and we'd like
 247                                  * to unprotect it, drop it; the next page
 248                                  * fault will trigger without uffd trapping.
 249                                  */
 250                                 if (uffd_wp_resolve) {
 251                                         pte_clear(vma->vm_mm, addr, pte);
 252                                         pages++;
 253                                 }
 254                                 continue;
 255                         } else {
 256                                 newpte = oldpte;
 257                         }
 258
 259                         if (uffd_wp)
 260                                 newpte = pte_swp_mkuffd_wp(newpte);
 261                         else if (uffd_wp_resolve)
 262                                 newpte = pte_swp_clear_uffd_wp(newpte);
 263
 264                         if (!pte_same(oldpte, newpte)) {
 265                                 set_pte_at(vma->vm_mm, addr, pte, newpte);
 266                                 pages++;
 267                         }
 268                 } else {
 269                         /* It must be an none page, or what else?.. */
 270                         WARN_ON_ONCE(!pte_none(oldpte));
 271
 272                         /*
 273                          * Nobody plays with any none ptes besides
 274                          * userfaultfd when applying the protections.
 275                          */
 276                         if (likely(!uffd_wp))
 277                                 continue;
 278
 279                         if (userfaultfd_wp_use_markers(vma)) {
 280                                 /*
 281                                  * For file-backed mem, we need to be able to
 282                                  * wr-protect a none pte, because even if the
 283                                  * pte is none, the page/swap cache could
 284                                  * exist.  Doing that by install a marker.
 285                                  */
 286                                 set_pte_at(vma->vm_mm, addr, pte,
 287                                            make_pte_marker(PTE_MARKER_UFFD_WP));
 288                                 pages++;
 289                         }
 290                 }
 291         } while (pte++, addr += PAGE_SIZE, addr != end);
 292         arch_leave_lazy_mmu_mode();
 293         pte_unmap_unlock(pte - 1, ptl);
 294
 295         return pages;
 296 }
 297
 298 /*
 299  * Return true if we want to split THPs into PTE mappings in change
 300  * protection procedure, false otherwise.
 301  */
 302 static inline bool
 303 pgtable_split_needed(struct vm_area_struct *vma, unsigned long cp_flags)
 304 {
 305         /*
 306          * pte markers only resides in pte level, if we need pte markers,
 307          * we need to split.  For example, we cannot wr-protect a file thp
 308          * (e.g. 2M shmem) because file thp is handled differently when
 309          * split by erasing the pmd so far.
 310          */
 311         return (cp_flags & MM_CP_UFFD_WP) && !vma_is_anonymous(vma);
 312 }
 313
 314 /*
 315  * Return true if we want to populate pgtables in change protection
 316  * procedure, false otherwise
 317  */
 318 static inline bool
 319 pgtable_populate_needed(struct vm_area_struct *vma, unsigned long cp_flags)
 320 {
 321         /* If not within ioctl(UFFDIO_WRITEPROTECT), then don't bother */
 322         if (!(cp_flags & MM_CP_UFFD_WP))
 323                 return false;
 324
 325         /* Populate if the userfaultfd mode requires pte markers */
 326         return userfaultfd_wp_use_markers(vma);
 327 }
 328
 329 /*
 330  * Populate the pgtable underneath for whatever reason if requested.
 331  * When {pte|pmd|...}_alloc() failed we treat it the same way as pgtable
 332  * allocation failures during page faults by kicking OOM and returning
 333  * error.
 334  */
 335 #define  change_pmd_prepare(vma, pmd, cp_flags)                         \
 336         ({                                                              \
 337                 long err = 0;                                           \
 338                 if (unlikely(pgtable_populate_needed(vma, cp_flags))) { \
 339                         if (pte_alloc(vma->vm_mm, pmd))                 \
 340                                 err = -ENOMEM;                          \
 341                 }                                                       \
 342                 err;                                                    \
 343         })
 344
 345 /*
 346  * This is the general pud/p4d/pgd version of change_pmd_prepare(). We need to
 347  * have separate change_pmd_prepare() because pte_alloc() returns 0 on success,
 348  * while {pmd|pud|p4d}_alloc() returns the valid pointer on success.
 349  */
 350 #define  change_prepare(vma, high, low, addr, cp_flags)                 \
 351           ({                                                            \
 352                 long err = 0;                                           \
 353                 if (unlikely(pgtable_populate_needed(vma, cp_flags))) { \
 354                         low##_t *p = low##_alloc(vma->vm_mm, high, addr); \
 355                         if (p == NULL)                                  \
 356                                 err = -ENOMEM;                          \
 357                 }                                                       \
 358                 err;                                                    \
 359         })
 360
 361 static inline long change_pmd_range(struct mmu_gather *tlb,
 362                 struct vm_area_struct *vma, pud_t *pud, unsigned long addr,
 363                 unsigned long end, pgprot_t newprot, unsigned long cp_flags)
 364 {
 365         pmd_t *pmd;
 366         unsigned long next;
 367         long pages = 0;
 368         unsigned long nr_huge_updates = 0;
 369
 370         pmd = pmd_offset(pud, addr);
 371         do {
 372                 long ret;
 373                 pmd_t _pmd;
 374 again:
 375                 next = pmd_addr_end(addr, end);
 376
 377                 ret = change_pmd_prepare(vma, pmd, cp_flags);
 378                 if (ret) {
 379                         pages = ret;
 380                         break;
 381                 }
 382
 383                 if (pmd_none(*pmd))
 384                         goto next;
 385
 386                 _pmd = pmdp_get_lockless(pmd);
 387                 if (is_swap_pmd(_pmd) || pmd_trans_huge(_pmd) || pmd_devmap(_pmd)) {
 388                         if ((next - addr != HPAGE_PMD_SIZE) ||
 389                             pgtable_split_needed(vma, cp_flags)) {
 390                                 __split_huge_pmd(vma, pmd, addr, false, NULL);
 391                                 /*
 392                                  * For file-backed, the pmd could have been
 393                                  * cleared; make sure pmd populated if
 394                                  * necessary, then fall-through to pte level.
 395                                  */
 396                                 ret = change_pmd_prepare(vma, pmd, cp_flags);
 397                                 if (ret) {
 398                                         pages = ret;
 399                                         break;
 400                                 }
 401                         } else {
 402                                 ret = change_huge_pmd(tlb, vma, pmd,
 403                                                 addr, newprot, cp_flags);
 404                                 if (ret) {
 405                                         if (ret == HPAGE_PMD_NR) {
 406                                                 pages += HPAGE_PMD_NR;
 407                                                 nr_huge_updates++;
 408                                         }
 409
 410                                         /* huge pmd was handled */
 411                                         goto next;
 412                                 }
 413                         }
 414                         /* fall through, the trans huge pmd just split */
 415                 }
 416
 417                 ret = change_pte_range(tlb, vma, pmd, addr, next, newprot,
 418                                        cp_flags);
 419                 if (ret < 0)
 420                         goto again;
 421                 pages += ret;
 422 next:
 423                 cond_resched();
 424         } while (pmd++, addr = next, addr != end);
 425
 426         if (nr_huge_updates)
 427                 count_vm_numa_events(NUMA_HUGE_PTE_UPDATES, nr_huge_updates);
 428         return pages;
 429 }
 430
 431 static inline long change_pud_range(struct mmu_gather *tlb,
 432                 struct vm_area_struct *vma, p4d_t *p4d, unsigned long addr,
 433                 unsigned long end, pgprot_t newprot, unsigned long cp_flags)
 434 {
 435         struct mmu_notifier_range range;
 436         pud_t *pudp, pud;
 437         unsigned long next;
 438         long pages = 0, ret;
 439
 440         range.start = 0;
 441
 442         pudp = pud_offset(p4d, addr);
 443         do {
 444 again:
 445                 next = pud_addr_end(addr, end);
 446                 ret = change_prepare(vma, pudp, pmd, addr, cp_flags);
 447                 if (ret) {
 448                         pages = ret;
 449                         break;
 450                 }
 451
 452                 pud = READ_ONCE(*pudp);
 453                 if (pud_none(pud))
 454                         continue;
 455
 456                 if (!range.start) {
 457                         mmu_notifier_range_init(&range,
 458                                                 MMU_NOTIFY_PROTECTION_VMA, 0,
 459                                                 vma->vm_mm, addr, end);
 460                         mmu_notifier_invalidate_range_start(&range);
 461                 }
 462
 463                 if (pud_leaf(pud)) {
 464                         if ((next - addr != PUD_SIZE) ||
 465                             pgtable_split_needed(vma, cp_flags)) {
 466                                 __split_huge_pud(vma, pudp, addr);
 467                                 goto again;
 468                         } else {
 469                                 ret = change_huge_pud(tlb, vma, pudp,
 470                                                       addr, newprot, cp_flags);
 471                                 if (ret == 0)
 472                                         goto again;
 473                                 /* huge pud was handled */
 474                                 if (ret == HPAGE_PUD_NR)
 475                                         pages += HPAGE_PUD_NR;
 476                                 continue;
 477                         }
 478                 }
 479
 480                 pages += change_pmd_range(tlb, vma, pudp, addr, next, newprot,
 481                                           cp_flags);
 482         } while (pudp++, addr = next, addr != end);
 483
 484         if (range.start)
 485                 mmu_notifier_invalidate_range_end(&range);
 486
 487         return pages;
 488 }
 489
 490 static inline long change_p4d_range(struct mmu_gather *tlb,
 491                 struct vm_area_struct *vma, pgd_t *pgd, unsigned long addr,
 492                 unsigned long end, pgprot_t newprot, unsigned long cp_flags)
 493 {
 494         p4d_t *p4d;
 495         unsigned long next;
 496         long pages = 0, ret;
 497
 498         p4d = p4d_offset(pgd, addr);
 499         do {
 500                 next = p4d_addr_end(addr, end);
 501                 ret = change_prepare(vma, p4d, pud, addr, cp_flags);
 502                 if (ret)
 503                         return ret;
 504                 if (p4d_none_or_clear_bad(p4d))
 505                         continue;
 506                 pages += change_pud_range(tlb, vma, p4d, addr, next, newprot,
 507                                           cp_flags);
 508         } while (p4d++, addr = next, addr != end);
 509
 510         return pages;
 511 }
 512
 513 static long change_protection_range(struct mmu_gather *tlb,
 514                 struct vm_area_struct *vma, unsigned long addr,
 515                 unsigned long end, pgprot_t newprot, unsigned long cp_flags)
 516 {
 517         struct mm_struct *mm = vma->vm_mm;
 518         pgd_t *pgd;
 519         unsigned long next;
 520         long pages = 0, ret;
 521
 522         BUG_ON(addr >= end);
 523         pgd = pgd_offset(mm, addr);
 524         tlb_start_vma(tlb, vma);
 525         do {
 526                 next = pgd_addr_end(addr, end);
 527                 ret = change_prepare(vma, pgd, p4d, addr, cp_flags);
 528                 if (ret) {
 529                         pages = ret;
 530                         break;
 531                 }
 532                 if (pgd_none_or_clear_bad(pgd))
 533                         continue;
 534                 pages += change_p4d_range(tlb, vma, pgd, addr, next, newprot,
 535                                           cp_flags);
 536         } while (pgd++, addr = next, addr != end);
 537
 538         tlb_end_vma(tlb, vma);
 539
 540         return pages;
 541 }
 542
 543 long change_protection(struct mmu_gather *tlb,
 544                        struct vm_area_struct *vma, unsigned long start,
 545                        unsigned long end, unsigned long cp_flags)
 546 {
 547         pgprot_t newprot = vma->vm_page_prot;
 548         long pages;
 549
 550         BUG_ON((cp_flags & MM_CP_UFFD_WP_ALL) == MM_CP_UFFD_WP_ALL);
 551
 552 #ifdef CONFIG_NUMA_BALANCING
 553         /*
 554          * Ordinary protection updates (mprotect, uffd-wp, softdirty tracking)
 555          * are expected to reflect their requirements via VMA flags such that
 556          * vma_set_page_prot() will adjust vma->vm_page_prot accordingly.
 557          */
 558         if (cp_flags & MM_CP_PROT_NUMA)
 559                 newprot = PAGE_NONE;
 560 #else
 561         WARN_ON_ONCE(cp_flags & MM_CP_PROT_NUMA);
 562 #endif
 563
 564         if (is_vm_hugetlb_page(vma))
 565                 pages = hugetlb_change_protection(vma, start, end, newprot,
 566                                                   cp_flags);
 567         else
 568                 pages = change_protection_range(tlb, vma, start, end, newprot,
 569                                                 cp_flags);
 570
 571         return pages;
 572 }
 573
 574 static int prot_none_pte_entry(pte_t *pte, unsigned long addr,
 575                                unsigned long next, struct mm_walk *walk)
 576 {
 577         return pfn_modify_allowed(pte_pfn(ptep_get(pte)),
 578                                   *(pgprot_t *)(walk->private)) ?
 579                 0 : -EACCES;
 580 }
 581
 582 static int prot_none_hugetlb_entry(pte_t *pte, unsigned long hmask,
 583                                    unsigned long addr, unsigned long next,
 584                                    struct mm_walk *walk)
 585 {
 586         return pfn_modify_allowed(pte_pfn(ptep_get(pte)),
 587                                   *(pgprot_t *)(walk->private)) ?
 588                 0 : -EACCES;
 589 }
 590
 591 static int prot_none_test(unsigned long addr, unsigned long next,
 592                           struct mm_walk *walk)
 593 {
 594         return 0;
 595 }
 596
 597 static const struct mm_walk_ops prot_none_walk_ops = {
 598         .pte_entry              = prot_none_pte_entry,
 599         .hugetlb_entry          = prot_none_hugetlb_entry,
 600         .test_walk              = prot_none_test,
 601         .walk_lock              = PGWALK_WRLOCK,
 602 };
 603
 604 int
 605 mprotect_fixup(struct vma_iterator *vmi, struct mmu_gather *tlb,
 606                struct vm_area_struct *vma, struct vm_area_struct **pprev,
 607                unsigned long start, unsigned long end, unsigned long newflags)
 608 {
 609         struct mm_struct *mm = vma->vm_mm;
 610         unsigned long oldflags = vma->vm_flags;
 611         long nrpages = (end - start) >> PAGE_SHIFT;
 612         unsigned int mm_cp_flags = 0;
 613         unsigned long charged = 0;
 614         int error;
 615
 616         if (!can_modify_vma(vma))
 617                 return -EPERM;
 618
 619         if (newflags == oldflags) {
 620                 *pprev = vma;
 621                 return 0;
 622         }
 623
 624         /*
 625          * Do PROT_NONE PFN permission checks here when we can still
 626          * bail out without undoing a lot of state. This is a rather
 627          * uncommon case, so doesn't need to be very optimized.
 628          */
 629         if (arch_has_pfn_modify_check() &&
 630             (vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP)) &&
 631             (newflags & VM_ACCESS_FLAGS) == 0) {
 632                 pgprot_t new_pgprot = vm_get_page_prot(newflags);
 633
 634                 error = walk_page_range(current->mm, start, end,
 635                                 &prot_none_walk_ops, &new_pgprot);
 636                 if (error)
 637                         return error;
 638         }
 639
 640         /*
 641          * If we make a private mapping writable we increase our commit;
 642          * but (without finer accounting) cannot reduce our commit if we
 643          * make it unwritable again except in the anonymous case where no
 644          * anon_vma has yet to be assigned.
 645          *
 646          * hugetlb mapping were accounted for even if read-only so there is
 647          * no need to account for them here.
 648          */
 649         if (newflags & VM_WRITE) {
 650                 /* Check space limits when area turns into data. */
 651                 if (!may_expand_vm(mm, newflags, nrpages) &&
 652                                 may_expand_vm(mm, oldflags, nrpages))
 653                         return -ENOMEM;
 654                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
 655                                                 VM_SHARED|VM_NORESERVE))) {
 656                         charged = nrpages;
 657                         if (security_vm_enough_memory_mm(mm, charged))
 658                                 return -ENOMEM;
 659                         newflags |= VM_ACCOUNT;
 660                 }
 661         } else if ((oldflags & VM_ACCOUNT) && vma_is_anonymous(vma) &&
 662                    !vma->anon_vma) {
 663                 newflags &= ~VM_ACCOUNT;
 664         }
 665
 666         vma = vma_modify_flags(vmi, *pprev, vma, start, end, newflags);
 667         if (IS_ERR(vma)) {
 668                 error = PTR_ERR(vma);
 669                 goto fail;
 670         }
 671
 672         *pprev = vma;
 673
 674         /*
 675          * vm_flags and vm_page_prot are protected by the mmap_lock
 676          * held in write mode.
 677          */
 678         vma_start_write(vma);
 679         vm_flags_reset(vma, newflags);
 680         if (vma_wants_manual_pte_write_upgrade(vma))
 681                 mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE;
 682         vma_set_page_prot(vma);
 683
 684         change_protection(tlb, vma, start, end, mm_cp_flags);
 685
 686         if ((oldflags & VM_ACCOUNT) && !(newflags & VM_ACCOUNT))
 687                 vm_unacct_memory(nrpages);
 688
 689         /*
 690          * Private VM_LOCKED VMA becoming writable: trigger COW to avoid major
 691          * fault on access.
 692          */
 693         if ((oldflags & (VM_WRITE | VM_SHARED | VM_LOCKED)) == VM_LOCKED &&
 694                         (newflags & VM_WRITE)) {
 695                 populate_vma_page_range(vma, start, end, NULL);
 696         }
 697
 698         vm_stat_account(mm, oldflags, -nrpages);
 699         vm_stat_account(mm, newflags, nrpages);
 700         perf_event_mmap(vma);
 701         return 0;
 702
 703 fail:
 704         vm_unacct_memory(charged);
 705         return error;
 706 }
 707
 708 /*
 709  * pkey==-1 when doing a legacy mprotect()
 710  */
 711 static int do_mprotect_pkey(unsigned long start, size_t len,
 712                 unsigned long prot, int pkey)
 713 {
 714         unsigned long nstart, end, tmp, reqprot;
 715         struct vm_area_struct *vma, *prev;
 716         int error;
 717         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 718         const bool rier = (current->personality & READ_IMPLIES_EXEC) &&
 719                                 (prot & PROT_READ);
 720         struct mmu_gather tlb;
 721         struct vma_iterator vmi;
 722
 723         start = untagged_addr(start);
 724
 725         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 726         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 727                 return -EINVAL;
 728
 729         if (start & ~PAGE_MASK)
 730                 return -EINVAL;
 731         if (!len)
 732                 return 0;
 733         len = PAGE_ALIGN(len);
 734         end = start + len;
 735         if (end <= start)
 736                 return -ENOMEM;
 737         if (!arch_validate_prot(prot, start))
 738                 return -EINVAL;
 739
 740         reqprot = prot;
 741
 742         if (mmap_write_lock_killable(current->mm))
 743                 return -EINTR;
 744
 745         /*
 746          * If userspace did not allocate the pkey, do not let
 747          * them use it here.
 748          */
 749         error = -EINVAL;
 750         if ((pkey != -1) && !mm_pkey_is_allocated(current->mm, pkey))
 751                 goto out;
 752
 753         vma_iter_init(&vmi, current->mm, start);
 754         vma = vma_find(&vmi, end);
 755         error = -ENOMEM;
 756         if (!vma)
 757                 goto out;
 758
 759         if (unlikely(grows & PROT_GROWSDOWN)) {
 760                 if (vma->vm_start >= end)
 761                         goto out;
 762                 start = vma->vm_start;
 763                 error = -EINVAL;
 764                 if (!(vma->vm_flags & VM_GROWSDOWN))
 765                         goto out;
 766         } else {
 767                 if (vma->vm_start > start)
 768                         goto out;
 769                 if (unlikely(grows & PROT_GROWSUP)) {
 770                         end = vma->vm_end;
 771                         error = -EINVAL;
 772                         if (!(vma->vm_flags & VM_GROWSUP))
 773                                 goto out;
 774                 }
 775         }
 776
 777         prev = vma_prev(&vmi);
 778         if (start > vma->vm_start)
 779                 prev = vma;
 780
 781         tlb_gather_mmu(&tlb, current->mm);
 782         nstart = start;
 783         tmp = vma->vm_start;
 784         for_each_vma_range(vmi, vma, end) {
 785                 unsigned long mask_off_old_flags;
 786                 unsigned long newflags;
 787                 int new_vma_pkey;
 788
 789                 if (vma->vm_start != tmp) {
 790                         error = -ENOMEM;
 791                         break;
 792                 }
 793
 794                 /* Does the application expect PROT_READ to imply PROT_EXEC */
 795                 if (rier && (vma->vm_flags & VM_MAYEXEC))
 796                         prot |= PROT_EXEC;
 797
 798                 /*
 799                  * Each mprotect() call explicitly passes r/w/x permissions.
 800                  * If a permission is not passed to mprotect(), it must be
 801                  * cleared from the VMA.
 802                  */
 803                 mask_off_old_flags = VM_ACCESS_FLAGS | VM_FLAGS_CLEAR;
 804
 805                 new_vma_pkey = arch_override_mprotect_pkey(vma, prot, pkey);
 806                 newflags = calc_vm_prot_bits(prot, new_vma_pkey);
 807                 newflags |= (vma->vm_flags & ~mask_off_old_flags);
 808
 809                 /* newflags >> 4 shift VM_MAY% in place of VM_% */
 810                 if ((newflags & ~(newflags >> 4)) & VM_ACCESS_FLAGS) {
 811                         error = -EACCES;
 812                         break;
 813                 }
 814
 815                 if (map_deny_write_exec(vma->vm_flags, newflags)) {
 816                         error = -EACCES;
 817                         break;
 818                 }
 819
 820                 /* Allow architectures to sanity-check the new flags */
 821                 if (!arch_validate_flags(newflags)) {
 822                         error = -EINVAL;
 823                         break;
 824                 }
 825
 826                 error = security_file_mprotect(vma, reqprot, prot);
 827                 if (error)
 828                         break;
 829
 830                 tmp = vma->vm_end;
 831                 if (tmp > end)
 832                         tmp = end;
 833
 834                 if (vma->vm_ops && vma->vm_ops->mprotect) {
 835                         error = vma->vm_ops->mprotect(vma, nstart, tmp, newflags);
 836                         if (error)
 837                                 break;
 838                 }
 839
 840                 error = mprotect_fixup(&vmi, &tlb, vma, &prev, nstart, tmp, newflags);
 841                 if (error)
 842                         break;
 843
 844                 tmp = vma_iter_end(&vmi);
 845                 nstart = tmp;
 846                 prot = reqprot;
 847         }
 848         tlb_finish_mmu(&tlb);
 849
 850         if (!error && tmp < end)
 851                 error = -ENOMEM;
 852
 853 out:
 854         mmap_write_unlock(current->mm);
 855         return error;
 856 }
 857
 858 SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 859                 unsigned long, prot)
 860 {
 861         return do_mprotect_pkey(start, len, prot, -1);
 862 }
 863
 864 #ifdef CONFIG_ARCH_HAS_PKEYS
 865
 866 SYSCALL_DEFINE4(pkey_mprotect, unsigned long, start, size_t, len,
 867                 unsigned long, prot, int, pkey)
 868 {
 869         return do_mprotect_pkey(start, len, prot, pkey);
 870 }
 871
 872 SYSCALL_DEFINE2(pkey_alloc, unsigned long, flags, unsigned long, init_val)
 873 {
 874         int pkey;
 875         int ret;
 876
 877         /* No flags supported yet. */
 878         if (flags)
 879                 return -EINVAL;
 880         /* check for unsupported init values */
 881         if (init_val & ~PKEY_ACCESS_MASK)
 882                 return -EINVAL;
 883
 884         mmap_write_lock(current->mm);
 885         pkey = mm_pkey_alloc(current->mm);
 886
 887         ret = -ENOSPC;
 888         if (pkey == -1)
 889                 goto out;
 890
 891         ret = arch_set_user_pkey_access(current, pkey, init_val);
 892         if (ret) {
 893                 mm_pkey_free(current->mm, pkey);
 894                 goto out;
 895         }
 896         ret = pkey;
 897 out:
 898         mmap_write_unlock(current->mm);
 899         return ret;
 900 }
 901
 902 SYSCALL_DEFINE1(pkey_free, int, pkey)
 903 {
 904         int ret;
 905
 906         mmap_write_lock(current->mm);
 907         ret = mm_pkey_free(current->mm, pkey);
 908         mmap_write_unlock(current->mm);
 909
 910         /*
 911          * We could provide warnings or errors if any VMA still
 912          * has the pkey set here.
 913          */
 914         return ret;
 915 }
 916
 917 #endif /* CONFIG_ARCH_HAS_PKEYS */