LXR linux/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 <linux/ksm.h>
  27#include <linux/pkeys.h>
  28#include <asm/uaccess.h>
  29#include <asm/pgtable.h>
  30#include <asm/cacheflush.h>
  31#include <asm/tlbflush.h>
  32
  33#include "internal.h"
  34
  35/*
  36 * For a prot_numa update we only hold mmap_sem for read so there is a
  37 * potential race with faulting where a pmd was temporarily none. This
  38 * function checks for a transhuge pmd under the appropriate lock. It
  39 * returns a pte if it was successfully locked or NULL if it raced with
  40 * a transhuge insertion.
  41 */
  42static pte_t *lock_pte_protection(struct vm_area_struct *vma, pmd_t *pmd,
  43                        unsigned long addr, int prot_numa, spinlock_t **ptl)
  44{
  45        pte_t *pte;
  46        spinlock_t *pmdl;
  47
  48        /* !prot_numa is protected by mmap_sem held for write */
  49        if (!prot_numa)
  50                return pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
  51
  52        pmdl = pmd_lock(vma->vm_mm, pmd);
  53        if (unlikely(pmd_trans_huge(*pmd) || pmd_none(*pmd))) {
  54                spin_unlock(pmdl);
  55                return NULL;
  56        }
  57
  58        pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
  59        spin_unlock(pmdl);
  60        return pte;
  61}
  62
  63static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
  64                unsigned long addr, unsigned long end, pgprot_t newprot,
  65                int dirty_accountable, int prot_numa)
  66{
  67        struct mm_struct *mm = vma->vm_mm;
  68        pte_t *pte, oldpte;
  69        spinlock_t *ptl;
  70        unsigned long pages = 0;
  71
  72        pte = lock_pte_protection(vma, pmd, addr, prot_numa, &ptl);
  73        if (!pte)
  74                return 0;
  75
  76        arch_enter_lazy_mmu_mode();
  77        do {
  78                oldpte = *pte;
  79                if (pte_present(oldpte)) {
  80                        pte_t ptent;
  81                        bool preserve_write = prot_numa && pte_write(oldpte);
  82
  83                        /*
  84                         * Avoid trapping faults against the zero or KSM
  85                         * pages. See similar comment in change_huge_pmd.
  86                         */
  87                        if (prot_numa) {
  88                                struct page *page;
  89
  90                                page = vm_normal_page(vma, addr, oldpte);
  91                                if (!page || PageKsm(page))
  92                                        continue;
  93
  94                                /* Avoid TLB flush if possible */
  95                                if (pte_protnone(oldpte))
  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_mkwrite(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        } while (pte++, addr += PAGE_SIZE, addr != end);
 131        arch_leave_lazy_mmu_mode();
 132        pte_unmap_unlock(pte - 1, ptl);
 133
 134        return pages;
 135}
 136
 137static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
 138                pud_t *pud, unsigned long addr, unsigned long end,
 139                pgprot_t newprot, int dirty_accountable, int prot_numa)
 140{
 141        pmd_t *pmd;
 142        struct mm_struct *mm = vma->vm_mm;
 143        unsigned long next;
 144        unsigned long pages = 0;
 145        unsigned long nr_huge_updates = 0;
 146        unsigned long mni_start = 0;
 147
 148        pmd = pmd_offset(pud, addr);
 149        do {
 150                unsigned long this_pages;
 151
 152                next = pmd_addr_end(addr, end);
 153                if (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd)
 154                                && pmd_none_or_clear_bad(pmd))
 155                        continue;
 156
 157                /* invoke the mmu notifier if the pmd is populated */
 158                if (!mni_start) {
 159                        mni_start = addr;
 160                        mmu_notifier_invalidate_range_start(mm, mni_start, end);
 161                }
 162
 163                if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
 164                        if (next - addr != HPAGE_PMD_SIZE) {
 165                                split_huge_pmd(vma, pmd, addr);
 166                                if (pmd_none(*pmd))
 167                                        continue;
 168                        } else {
 169                                int nr_ptes = change_huge_pmd(vma, pmd, addr,
 170                                                newprot, prot_numa);
 171
 172                                if (nr_ptes) {
 173                                        if (nr_ptes == HPAGE_PMD_NR) {
 174                                                pages += HPAGE_PMD_NR;
 175                                                nr_huge_updates++;
 176                                        }
 177
 178                                        /* huge pmd was handled */
 179                                        continue;
 180                                }
 181                        }
 182                        /* fall through, the trans huge pmd just split */
 183                }
 184                this_pages = change_pte_range(vma, pmd, addr, next, newprot,
 185                                 dirty_accountable, prot_numa);
 186                pages += this_pages;
 187        } while (pmd++, addr = next, addr != end);
 188
 189        if (mni_start)
 190                mmu_notifier_invalidate_range_end(mm, mni_start, end);
 191
 192        if (nr_huge_updates)
 193                count_vm_numa_events(NUMA_HUGE_PTE_UPDATES, nr_huge_updates);
 194        return pages;
 195}
 196
 197static inline unsigned long change_pud_range(struct vm_area_struct *vma,
 198                pgd_t *pgd, unsigned long addr, unsigned long end,
 199                pgprot_t newprot, int dirty_accountable, int prot_numa)
 200{
 201        pud_t *pud;
 202        unsigned long next;
 203        unsigned long pages = 0;
 204
 205        pud = pud_offset(pgd, addr);
 206        do {
 207                next = pud_addr_end(addr, end);
 208                if (pud_none_or_clear_bad(pud))
 209                        continue;
 210                pages += change_pmd_range(vma, pud, addr, next, newprot,
 211                                 dirty_accountable, prot_numa);
 212        } while (pud++, addr = next, addr != end);
 213
 214        return pages;
 215}
 216
 217static unsigned long change_protection_range(struct vm_area_struct *vma,
 218                unsigned long addr, unsigned long end, pgprot_t newprot,
 219                int dirty_accountable, int prot_numa)
 220{
 221        struct mm_struct *mm = vma->vm_mm;
 222        pgd_t *pgd;
 223        unsigned long next;
 224        unsigned long start = addr;
 225        unsigned long pages = 0;
 226
 227        BUG_ON(addr >= end);
 228        pgd = pgd_offset(mm, addr);
 229        flush_cache_range(vma, addr, end);
 230        set_tlb_flush_pending(mm);
 231        do {
 232                next = pgd_addr_end(addr, end);
 233                if (pgd_none_or_clear_bad(pgd))
 234                        continue;
 235                pages += change_pud_range(vma, pgd, addr, next, newprot,
 236                                 dirty_accountable, prot_numa);
 237        } while (pgd++, addr = next, addr != end);
 238
 239        /* Only flush the TLB if we actually modified any entries: */
 240        if (pages)
 241                flush_tlb_range(vma, start, end);
 242        clear_tlb_flush_pending(mm);
 243
 244        return pages;
 245}
 246
 247unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
 248                       unsigned long end, pgprot_t newprot,
 249                       int dirty_accountable, int prot_numa)
 250{
 251        unsigned long pages;
 252
 253        if (is_vm_hugetlb_page(vma))
 254                pages = hugetlb_change_protection(vma, start, end, newprot);
 255        else
 256                pages = change_protection_range(vma, start, end, newprot, dirty_accountable, prot_numa);
 257
 258        return pages;
 259}
 260
 261int
 262mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 263        unsigned long start, unsigned long end, unsigned long newflags)
 264{
 265        struct mm_struct *mm = vma->vm_mm;
 266        unsigned long oldflags = vma->vm_flags;
 267        long nrpages = (end - start) >> PAGE_SHIFT;
 268        unsigned long charged = 0;
 269        pgoff_t pgoff;
 270        int error;
 271        int dirty_accountable = 0;
 272
 273        if (newflags == oldflags) {
 274                *pprev = vma;
 275                return 0;
 276        }
 277
 278        /*
 279         * If we make a private mapping writable we increase our commit;
 280         * but (without finer accounting) cannot reduce our commit if we
 281         * make it unwritable again. hugetlb mapping were accounted for
 282         * even if read-only so there is no need to account for them here
 283         */
 284        if (newflags & VM_WRITE) {
 285                /* Check space limits when area turns into data. */
 286                if (!may_expand_vm(mm, newflags, nrpages) &&
 287                                may_expand_vm(mm, oldflags, nrpages))
 288                        return -ENOMEM;
 289                if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
 290                                                VM_SHARED|VM_NORESERVE))) {
 291                        charged = nrpages;
 292                        if (security_vm_enough_memory_mm(mm, charged))
 293                                return -ENOMEM;
 294                        newflags |= VM_ACCOUNT;
 295                }
 296        }
 297
 298        /*
 299         * First try to merge with previous and/or next vma.
 300         */
 301        pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 302        *pprev = vma_merge(mm, *pprev, start, end, newflags,
 303                           vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
 304                           vma->vm_userfaultfd_ctx);
 305        if (*pprev) {
 306                vma = *pprev;
 307                goto success;
 308        }
 309
 310        *pprev = vma;
 311
 312        if (start != vma->vm_start) {
 313                error = split_vma(mm, vma, start, 1);
 314                if (error)
 315                        goto fail;
 316        }
 317
 318        if (end != vma->vm_end) {
 319                error = split_vma(mm, vma, end, 0);
 320                if (error)
 321                        goto fail;
 322        }
 323
 324success:
 325        /*
 326         * vm_flags and vm_page_prot are protected by the mmap_sem
 327         * held in write mode.
 328         */
 329        vma->vm_flags = newflags;
 330        dirty_accountable = vma_wants_writenotify(vma);
 331        vma_set_page_prot(vma);
 332
 333        change_protection(vma, start, end, vma->vm_page_prot,
 334                          dirty_accountable, 0);
 335
 336        /*
 337         * Private VM_LOCKED VMA becoming writable: trigger COW to avoid major
 338         * fault on access.
 339         */
 340        if ((oldflags & (VM_WRITE | VM_SHARED | VM_LOCKED)) == VM_LOCKED &&
 341                        (newflags & VM_WRITE)) {
 342                populate_vma_page_range(vma, start, end, NULL);
 343        }
 344
 345        vm_stat_account(mm, oldflags, -nrpages);
 346        vm_stat_account(mm, newflags, nrpages);
 347        perf_event_mmap(vma);
 348        return 0;
 349
 350fail:
 351        vm_unacct_memory(charged);
 352        return error;
 353}
 354
 355SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 356                unsigned long, prot)
 357{
 358        unsigned long nstart, end, tmp, reqprot;
 359        struct vm_area_struct *vma, *prev;
 360        int error = -EINVAL;
 361        const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 362        const bool rier = (current->personality & READ_IMPLIES_EXEC) &&
 363                                (prot & PROT_READ);
 364
 365        prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 366        if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 367                return -EINVAL;
 368
 369        if (start & ~PAGE_MASK)
 370                return -EINVAL;
 371        if (!len)
 372                return 0;
 373        len = PAGE_ALIGN(len);
 374        end = start + len;
 375        if (end <= start)
 376                return -ENOMEM;
 377        if (!arch_validate_prot(prot))
 378                return -EINVAL;
 379
 380        reqprot = prot;
 381
 382        down_write(&current->mm->mmap_sem);
 383
 384        vma = find_vma(current->mm, start);
 385        error = -ENOMEM;
 386        if (!vma)
 387                goto out;
 388        prev = vma->vm_prev;
 389        if (unlikely(grows & PROT_GROWSDOWN)) {
 390                if (vma->vm_start >= end)
 391                        goto out;
 392                start = vma->vm_start;
 393                error = -EINVAL;
 394                if (!(vma->vm_flags & VM_GROWSDOWN))
 395                        goto out;
 396        } else {
 397                if (vma->vm_start > start)
 398                        goto out;
 399                if (unlikely(grows & PROT_GROWSUP)) {
 400                        end = vma->vm_end;
 401                        error = -EINVAL;
 402                        if (!(vma->vm_flags & VM_GROWSUP))
 403                                goto out;
 404                }
 405        }
 406        if (start > vma->vm_start)
 407                prev = vma;
 408
 409        for (nstart = start ; ; ) {
 410                unsigned long newflags;
 411                int pkey = arch_override_mprotect_pkey(vma, prot, -1);
 412
 413                /* Here we know that vma->vm_start <= nstart < vma->vm_end. */
 414
 415                /* Does the application expect PROT_READ to imply PROT_EXEC */
 416                if (rier && (vma->vm_flags & VM_MAYEXEC))
 417                        prot |= PROT_EXEC;
 418
 419                newflags = calc_vm_prot_bits(prot, pkey);
 420                newflags |= (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 421
 422                /* newflags >> 4 shift VM_MAY% in place of VM_% */
 423                if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 424                        error = -EACCES;
 425                        goto out;
 426                }
 427
 428                error = security_file_mprotect(vma, reqprot, prot);
 429                if (error)
 430                        goto out;
 431
 432                tmp = vma->vm_end;
 433                if (tmp > end)
 434                        tmp = end;
 435                error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 436                if (error)
 437                        goto out;
 438                nstart = tmp;
 439
 440                if (nstart < prev->vm_end)
 441                        nstart = prev->vm_end;
 442                if (nstart >= end)
 443                        goto out;
 444
 445                vma = prev->vm_next;
 446                if (!vma || vma->vm_start != nstart) {
 447                        error = -ENOMEM;
 448                        goto out;
 449                }
 450                prot = reqprot;
 451        }
 452out:
 453        up_write(&current->mm->mmap_sem);
 454        return error;
 455}
 456