linux/mm/mprotect.c
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   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 <linux/pkeys.h>
  27#include <linux/ksm.h>
  28#include <asm/uaccess.h>
  29#include <asm/pgtable.h>
  30#include <asm/cacheflush.h>
  31#include <asm/mmu_context.h>
  32#include <asm/tlbflush.h>
  33
  34#include "internal.h"
  35
  36/*
  37 * For a prot_numa update we only hold mmap_sem for read so there is a
  38 * potential race with faulting where a pmd was temporarily none. This
  39 * function checks for a transhuge pmd under the appropriate lock. It
  40 * returns a pte if it was successfully locked or NULL if it raced with
  41 * a transhuge insertion.
  42 */
  43static pte_t *lock_pte_protection(struct vm_area_struct *vma, pmd_t *pmd,
  44                        unsigned long addr, int prot_numa, spinlock_t **ptl)
  45{
  46        pte_t *pte;
  47        spinlock_t *pmdl;
  48
  49        /* !prot_numa is protected by mmap_sem held for write */
  50        if (!prot_numa)
  51                return pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
  52
  53        pmdl = pmd_lock(vma->vm_mm, pmd);
  54        if (unlikely(pmd_trans_huge(*pmd) || pmd_none(*pmd))) {
  55                spin_unlock(pmdl);
  56                return NULL;
  57        }
  58
  59        pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
  60        spin_unlock(pmdl);
  61        return pte;
  62}
  63
  64static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
  65                unsigned long addr, unsigned long end, pgprot_t newprot,
  66                int dirty_accountable, int prot_numa)
  67{
  68        struct mm_struct *mm = vma->vm_mm;
  69        pte_t *pte, oldpte;
  70        spinlock_t *ptl;
  71        unsigned long pages = 0;
  72
  73        pte = lock_pte_protection(vma, pmd, addr, prot_numa, &ptl);
  74        if (!pte)
  75                return 0;
  76
  77        arch_enter_lazy_mmu_mode();
  78        do {
  79                oldpte = *pte;
  80                if (pte_present(oldpte)) {
  81                        pte_t ptent;
  82                        bool preserve_write = prot_numa && pte_write(oldpte);
  83
  84                        /*
  85                         * Avoid trapping faults against the zero or KSM
  86                         * pages. See similar comment in change_huge_pmd.
  87                         */
  88                        if (prot_numa) {
  89                                struct page *page;
  90
  91                                page = vm_normal_page(vma, addr, oldpte);
  92                                if (!page || PageKsm(page))
  93                                        continue;
  94
  95                                /* Avoid TLB flush if possible */
  96                                if (pte_protnone(oldpte))
  97                                        continue;
  98                        }
  99
 100                        ptent = ptep_modify_prot_start(mm, addr, pte);
 101                        ptent = pte_modify(ptent, newprot);
 102                        if (preserve_write)
 103                                ptent = pte_mkwrite(ptent);
 104
 105                        /* Avoid taking write faults for known dirty pages */
 106                        if (dirty_accountable && pte_dirty(ptent) &&
 107                                        (pte_soft_dirty(ptent) ||
 108                                         !(vma->vm_flags & VM_SOFTDIRTY))) {
 109                                ptent = pte_mkwrite(ptent);
 110                        }
 111                        ptep_modify_prot_commit(mm, addr, pte, ptent);
 112                        pages++;
 113                } else if (IS_ENABLED(CONFIG_MIGRATION)) {
 114                        swp_entry_t entry = pte_to_swp_entry(oldpte);
 115
 116                        if (is_write_migration_entry(entry)) {
 117                                pte_t newpte;
 118                                /*
 119                                 * A protection check is difficult so
 120                                 * just be safe and disable write
 121                                 */
 122                                make_migration_entry_read(&entry);
 123                                newpte = swp_entry_to_pte(entry);
 124                                if (pte_swp_soft_dirty(oldpte))
 125                                        newpte = pte_swp_mksoft_dirty(newpte);
 126                                set_pte_at(mm, addr, pte, newpte);
 127
 128                                pages++;
 129                        }
 130                }
 131        } while (pte++, addr += PAGE_SIZE, addr != end);
 132        arch_leave_lazy_mmu_mode();
 133        pte_unmap_unlock(pte - 1, ptl);
 134
 135        return pages;
 136}
 137
 138static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
 139                pud_t *pud, unsigned long addr, unsigned long end,
 140                pgprot_t newprot, int dirty_accountable, int prot_numa)
 141{
 142        pmd_t *pmd;
 143        struct mm_struct *mm = vma->vm_mm;
 144        unsigned long next;
 145        unsigned long pages = 0;
 146        unsigned long nr_huge_updates = 0;
 147        unsigned long mni_start = 0;
 148
 149        pmd = pmd_offset(pud, addr);
 150        do {
 151                unsigned long this_pages;
 152
 153                next = pmd_addr_end(addr, end);
 154                if (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd)
 155                                && pmd_none_or_clear_bad(pmd))
 156                        continue;
 157
 158                /* invoke the mmu notifier if the pmd is populated */
 159                if (!mni_start) {
 160                        mni_start = addr;
 161                        mmu_notifier_invalidate_range_start(mm, mni_start, end);
 162                }
 163
 164                if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
 165                        if (next - addr != HPAGE_PMD_SIZE) {
 166                                split_huge_pmd(vma, pmd, addr);
 167                                if (pmd_trans_unstable(pmd))
 168                                        continue;
 169                        } else {
 170                                int nr_ptes = change_huge_pmd(vma, pmd, addr,
 171                                                newprot, prot_numa);
 172
 173                                if (nr_ptes) {
 174                                        if (nr_ptes == HPAGE_PMD_NR) {
 175                                                pages += HPAGE_PMD_NR;
 176                                                nr_huge_updates++;
 177                                        }
 178
 179                                        /* huge pmd was handled */
 180                                        continue;
 181                                }
 182                        }
 183                        /* fall through, the trans huge pmd just split */
 184                }
 185                this_pages = change_pte_range(vma, pmd, addr, next, newprot,
 186                                 dirty_accountable, prot_numa);
 187                pages += this_pages;
 188        } while (pmd++, addr = next, addr != end);
 189
 190        if (mni_start)
 191                mmu_notifier_invalidate_range_end(mm, mni_start, end);
 192
 193        if (nr_huge_updates)
 194                count_vm_numa_events(NUMA_HUGE_PTE_UPDATES, nr_huge_updates);
 195        return pages;
 196}
 197
 198static inline unsigned long change_pud_range(struct vm_area_struct *vma,
 199                pgd_t *pgd, unsigned long addr, unsigned long end,
 200                pgprot_t newprot, int dirty_accountable, int prot_numa)
 201{
 202        pud_t *pud;
 203        unsigned long next;
 204        unsigned long pages = 0;
 205
 206        pud = pud_offset(pgd, addr);
 207        do {
 208                next = pud_addr_end(addr, end);
 209                if (pud_none_or_clear_bad(pud))
 210                        continue;
 211                pages += change_pmd_range(vma, pud, addr, next, newprot,
 212                                 dirty_accountable, prot_numa);
 213        } while (pud++, addr = next, addr != end);
 214
 215        return pages;
 216}
 217
 218static unsigned long change_protection_range(struct vm_area_struct *vma,
 219                unsigned long addr, unsigned long end, pgprot_t newprot,
 220                int dirty_accountable, int prot_numa)
 221{
 222        struct mm_struct *mm = vma->vm_mm;
 223        pgd_t *pgd;
 224        unsigned long next;
 225        unsigned long start = addr;
 226        unsigned long pages = 0;
 227
 228        BUG_ON(addr >= end);
 229        pgd = pgd_offset(mm, addr);
 230        flush_cache_range(vma, addr, end);
 231        set_tlb_flush_pending(mm);
 232        do {
 233                next = pgd_addr_end(addr, end);
 234                if (pgd_none_or_clear_bad(pgd))
 235                        continue;
 236                pages += change_pud_range(vma, pgd, addr, next, newprot,
 237                                 dirty_accountable, prot_numa);
 238        } while (pgd++, addr = next, addr != end);
 239
 240        /* Only flush the TLB if we actually modified any entries: */
 241        if (pages)
 242                flush_tlb_range(vma, start, end);
 243        clear_tlb_flush_pending(mm);
 244
 245        return pages;
 246}
 247
 248unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
 249                       unsigned long end, pgprot_t newprot,
 250                       int dirty_accountable, int prot_numa)
 251{
 252        unsigned long pages;
 253
 254        if (is_vm_hugetlb_page(vma))
 255                pages = hugetlb_change_protection(vma, start, end, newprot);
 256        else
 257                pages = change_protection_range(vma, start, end, newprot, dirty_accountable, prot_numa);
 258
 259        return pages;
 260}
 261
 262int
 263mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 264        unsigned long start, unsigned long end, unsigned long newflags)
 265{
 266        struct mm_struct *mm = vma->vm_mm;
 267        unsigned long oldflags = vma->vm_flags;
 268        long nrpages = (end - start) >> PAGE_SHIFT;
 269        unsigned long charged = 0;
 270        pgoff_t pgoff;
 271        int error;
 272        int dirty_accountable = 0;
 273
 274        if (newflags == oldflags) {
 275                *pprev = vma;
 276                return 0;
 277        }
 278
 279        /*
 280         * If we make a private mapping writable we increase our commit;
 281         * but (without finer accounting) cannot reduce our commit if we
 282         * make it unwritable again. hugetlb mapping were accounted for
 283         * even if read-only so there is no need to account for them here
 284         */
 285        if (newflags & VM_WRITE) {
 286                /* Check space limits when area turns into data. */
 287                if (!may_expand_vm(mm, newflags, nrpages) &&
 288                                may_expand_vm(mm, oldflags, nrpages))
 289                        return -ENOMEM;
 290                if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
 291                                                VM_SHARED|VM_NORESERVE))) {
 292                        charged = nrpages;
 293                        if (security_vm_enough_memory_mm(mm, charged))
 294                                return -ENOMEM;
 295                        newflags |= VM_ACCOUNT;
 296                }
 297        }
 298
 299        /*
 300         * First try to merge with previous and/or next vma.
 301         */
 302        pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 303        *pprev = vma_merge(mm, *pprev, start, end, newflags,
 304                           vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
 305                           vma->vm_userfaultfd_ctx);
 306        if (*pprev) {
 307                vma = *pprev;
 308                VM_WARN_ON((vma->vm_flags ^ newflags) & ~VM_SOFTDIRTY);
 309                goto success;
 310        }
 311
 312        *pprev = vma;
 313
 314        if (start != vma->vm_start) {
 315                error = split_vma(mm, vma, start, 1);
 316                if (error)
 317                        goto fail;
 318        }
 319
 320        if (end != vma->vm_end) {
 321                error = split_vma(mm, vma, end, 0);
 322                if (error)
 323                        goto fail;
 324        }
 325
 326success:
 327        /*
 328         * vm_flags and vm_page_prot are protected by the mmap_sem
 329         * held in write mode.
 330         */
 331        vma->vm_flags = newflags;
 332        dirty_accountable = vma_wants_writenotify(vma, vma->vm_page_prot);
 333        vma_set_page_prot(vma);
 334
 335        change_protection(vma, start, end, vma->vm_page_prot,
 336                          dirty_accountable, 0);
 337
 338        /*
 339         * Private VM_LOCKED VMA becoming writable: trigger COW to avoid major
 340         * fault on access.
 341         */
 342        if ((oldflags & (VM_WRITE | VM_SHARED | VM_LOCKED)) == VM_LOCKED &&
 343                        (newflags & VM_WRITE)) {
 344                populate_vma_page_range(vma, start, end, NULL);
 345        }
 346
 347        vm_stat_account(mm, oldflags, -nrpages);
 348        vm_stat_account(mm, newflags, nrpages);
 349        perf_event_mmap(vma);
 350        return 0;
 351
 352fail:
 353        vm_unacct_memory(charged);
 354        return error;
 355}
 356
 357/*
 358 * pkey==-1 when doing a legacy mprotect()
 359 */
 360static int do_mprotect_pkey(unsigned long start, size_t len,
 361                unsigned long prot, int pkey)
 362{
 363        unsigned long nstart, end, tmp, reqprot;
 364        struct vm_area_struct *vma, *prev;
 365        int error = -EINVAL;
 366        const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 367        const bool rier = (current->personality & READ_IMPLIES_EXEC) &&
 368                                (prot & PROT_READ);
 369
 370        prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 371        if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 372                return -EINVAL;
 373
 374        if (start & ~PAGE_MASK)
 375                return -EINVAL;
 376        if (!len)
 377                return 0;
 378        len = PAGE_ALIGN(len);
 379        end = start + len;
 380        if (end <= start)
 381                return -ENOMEM;
 382        if (!arch_validate_prot(prot))
 383                return -EINVAL;
 384
 385        reqprot = prot;
 386
 387        if (down_write_killable(&current->mm->mmap_sem))
 388                return -EINTR;
 389
 390        /*
 391         * If userspace did not allocate the pkey, do not let
 392         * them use it here.
 393         */
 394        error = -EINVAL;
 395        if ((pkey != -1) && !mm_pkey_is_allocated(current->mm, pkey))
 396                goto out;
 397
 398        vma = find_vma(current->mm, start);
 399        error = -ENOMEM;
 400        if (!vma)
 401                goto out;
 402        prev = vma->vm_prev;
 403        if (unlikely(grows & PROT_GROWSDOWN)) {
 404                if (vma->vm_start >= end)
 405                        goto out;
 406                start = vma->vm_start;
 407                error = -EINVAL;
 408                if (!(vma->vm_flags & VM_GROWSDOWN))
 409                        goto out;
 410        } else {
 411                if (vma->vm_start > start)
 412                        goto out;
 413                if (unlikely(grows & PROT_GROWSUP)) {
 414                        end = vma->vm_end;
 415                        error = -EINVAL;
 416                        if (!(vma->vm_flags & VM_GROWSUP))
 417                                goto out;
 418                }
 419        }
 420        if (start > vma->vm_start)
 421                prev = vma;
 422
 423        for (nstart = start ; ; ) {
 424                unsigned long mask_off_old_flags;
 425                unsigned long newflags;
 426                int new_vma_pkey;
 427
 428                /* Here we know that vma->vm_start <= nstart < vma->vm_end. */
 429
 430                /* Does the application expect PROT_READ to imply PROT_EXEC */
 431                if (rier && (vma->vm_flags & VM_MAYEXEC))
 432                        prot |= PROT_EXEC;
 433
 434                /*
 435                 * Each mprotect() call explicitly passes r/w/x permissions.
 436                 * If a permission is not passed to mprotect(), it must be
 437                 * cleared from the VMA.
 438                 */
 439                mask_off_old_flags = VM_READ | VM_WRITE | VM_EXEC |
 440                                        ARCH_VM_PKEY_FLAGS;
 441
 442                new_vma_pkey = arch_override_mprotect_pkey(vma, prot, pkey);
 443                newflags = calc_vm_prot_bits(prot, new_vma_pkey);
 444                newflags |= (vma->vm_flags & ~mask_off_old_flags);
 445
 446                /* newflags >> 4 shift VM_MAY% in place of VM_% */
 447                if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 448                        error = -EACCES;
 449                        goto out;
 450                }
 451
 452                error = security_file_mprotect(vma, reqprot, prot);
 453                if (error)
 454                        goto out;
 455
 456                tmp = vma->vm_end;
 457                if (tmp > end)
 458                        tmp = end;
 459                error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 460                if (error)
 461                        goto out;
 462                nstart = tmp;
 463
 464                if (nstart < prev->vm_end)
 465                        nstart = prev->vm_end;
 466                if (nstart >= end)
 467                        goto out;
 468
 469                vma = prev->vm_next;
 470                if (!vma || vma->vm_start != nstart) {
 471                        error = -ENOMEM;
 472                        goto out;
 473                }
 474                prot = reqprot;
 475        }
 476out:
 477        up_write(&current->mm->mmap_sem);
 478        return error;
 479}
 480
 481SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 482                unsigned long, prot)
 483{
 484        return do_mprotect_pkey(start, len, prot, -1);
 485}
 486
 487SYSCALL_DEFINE4(pkey_mprotect, unsigned long, start, size_t, len,
 488                unsigned long, prot, int, pkey)
 489{
 490        return do_mprotect_pkey(start, len, prot, pkey);
 491}
 492
 493SYSCALL_DEFINE2(pkey_alloc, unsigned long, flags, unsigned long, init_val)
 494{
 495        int pkey;
 496        int ret;
 497
 498        /* No flags supported yet. */
 499        if (flags)
 500                return -EINVAL;
 501        /* check for unsupported init values */
 502        if (init_val & ~PKEY_ACCESS_MASK)
 503                return -EINVAL;
 504
 505        down_write(&current->mm->mmap_sem);
 506        pkey = mm_pkey_alloc(current->mm);
 507
 508        ret = -ENOSPC;
 509        if (pkey == -1)
 510                goto out;
 511
 512        ret = arch_set_user_pkey_access(current, pkey, init_val);
 513        if (ret) {
 514                mm_pkey_free(current->mm, pkey);
 515                goto out;
 516        }
 517        ret = pkey;
 518out:
 519        up_write(&current->mm->mmap_sem);
 520        return ret;
 521}
 522
 523SYSCALL_DEFINE1(pkey_free, int, pkey)
 524{
 525        int ret;
 526
 527        down_write(&current->mm->mmap_sem);
 528        ret = mm_pkey_free(current->mm, pkey);
 529        up_write(&current->mm->mmap_sem);
 530
 531        /*
 532         * We could provie warnings or errors if any VMA still
 533         * has the pkey set here.
 534         */
 535        return ret;
 536}
 537