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 <asm/uaccess.h>
  27#include <asm/pgtable.h>
  28#include <asm/cacheflush.h>
  29#include <asm/tlbflush.h>
  30
  31#ifndef pgprot_modify
  32static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
  33{
  34        return newprot;
  35}
  36#endif
  37
  38static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
  39                unsigned long addr, unsigned long end, pgprot_t newprot,
  40                int dirty_accountable)
  41{
  42        pte_t *pte, oldpte;
  43        spinlock_t *ptl;
  44
  45        pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
  46        arch_enter_lazy_mmu_mode();
  47        do {
  48                oldpte = *pte;
  49                if (pte_present(oldpte)) {
  50                        pte_t ptent;
  51
  52                        ptent = ptep_modify_prot_start(mm, addr, pte);
  53                        ptent = pte_modify(ptent, newprot);
  54
  55                        /*
  56                         * Avoid taking write faults for pages we know to be
  57                         * dirty.
  58                         */
  59                        if (dirty_accountable && pte_dirty(ptent))
  60                                ptent = pte_mkwrite(ptent);
  61
  62                        ptep_modify_prot_commit(mm, addr, pte, ptent);
  63                } else if (PAGE_MIGRATION && !pte_file(oldpte)) {
  64                        swp_entry_t entry = pte_to_swp_entry(oldpte);
  65
  66                        if (is_write_migration_entry(entry)) {
  67                                /*
  68                                 * A protection check is difficult so
  69                                 * just be safe and disable write
  70                                 */
  71                                make_migration_entry_read(&entry);
  72                                set_pte_at(mm, addr, pte,
  73                                        swp_entry_to_pte(entry));
  74                        }
  75                }
  76        } while (pte++, addr += PAGE_SIZE, addr != end);
  77        arch_leave_lazy_mmu_mode();
  78        pte_unmap_unlock(pte - 1, ptl);
  79}
  80
  81static inline void change_pmd_range(struct vm_area_struct *vma, pud_t *pud,
  82                unsigned long addr, unsigned long end, pgprot_t newprot,
  83                int dirty_accountable)
  84{
  85        pmd_t *pmd;
  86        unsigned long next;
  87
  88        pmd = pmd_offset(pud, addr);
  89        do {
  90                next = pmd_addr_end(addr, end);
  91                if (pmd_trans_huge(*pmd)) {
  92                        if (next - addr != HPAGE_PMD_SIZE)
  93                                split_huge_page_pmd(vma->vm_mm, pmd);
  94                        else if (change_huge_pmd(vma, pmd, addr, newprot))
  95                                continue;
  96                        /* fall through */
  97                }
  98                if (pmd_none_or_clear_bad(pmd))
  99                        continue;
 100                change_pte_range(vma->vm_mm, pmd, addr, next, newprot,
 101                                 dirty_accountable);
 102        } while (pmd++, addr = next, addr != end);
 103}
 104
 105static inline void change_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
 106                unsigned long addr, unsigned long end, pgprot_t newprot,
 107                int dirty_accountable)
 108{
 109        pud_t *pud;
 110        unsigned long next;
 111
 112        pud = pud_offset(pgd, addr);
 113        do {
 114                next = pud_addr_end(addr, end);
 115                if (pud_none_or_clear_bad(pud))
 116                        continue;
 117                change_pmd_range(vma, pud, addr, next, newprot,
 118                                 dirty_accountable);
 119        } while (pud++, addr = next, addr != end);
 120}
 121
 122static void change_protection(struct vm_area_struct *vma,
 123                unsigned long addr, unsigned long end, pgprot_t newprot,
 124                int dirty_accountable)
 125{
 126        struct mm_struct *mm = vma->vm_mm;
 127        pgd_t *pgd;
 128        unsigned long next;
 129        unsigned long start = addr;
 130
 131        BUG_ON(addr >= end);
 132        pgd = pgd_offset(mm, addr);
 133        flush_cache_range(vma, addr, end);
 134        do {
 135                next = pgd_addr_end(addr, end);
 136                if (pgd_none_or_clear_bad(pgd))
 137                        continue;
 138                change_pud_range(vma, pgd, addr, next, newprot,
 139                                 dirty_accountable);
 140        } while (pgd++, addr = next, addr != end);
 141        flush_tlb_range(vma, start, end);
 142}
 143
 144int
 145mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
 146        unsigned long start, unsigned long end, unsigned long newflags)
 147{
 148        struct mm_struct *mm = vma->vm_mm;
 149        unsigned long oldflags = vma->vm_flags;
 150        long nrpages = (end - start) >> PAGE_SHIFT;
 151        unsigned long charged = 0;
 152        pgoff_t pgoff;
 153        int error;
 154        int dirty_accountable = 0;
 155
 156        if (newflags == oldflags) {
 157                *pprev = vma;
 158                return 0;
 159        }
 160
 161        /*
 162         * If we make a private mapping writable we increase our commit;
 163         * but (without finer accounting) cannot reduce our commit if we
 164         * make it unwritable again. hugetlb mapping were accounted for
 165         * even if read-only so there is no need to account for them here
 166         */
 167        if (newflags & VM_WRITE) {
 168                if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
 169                                                VM_SHARED|VM_NORESERVE))) {
 170                        charged = nrpages;
 171                        if (security_vm_enough_memory(charged))
 172                                return -ENOMEM;
 173                        newflags |= VM_ACCOUNT;
 174                }
 175        }
 176
 177        /*
 178         * First try to merge with previous and/or next vma.
 179         */
 180        pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
 181        *pprev = vma_merge(mm, *pprev, start, end, newflags,
 182                        vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
 183        if (*pprev) {
 184                vma = *pprev;
 185                goto success;
 186        }
 187
 188        *pprev = vma;
 189
 190        if (start != vma->vm_start) {
 191                error = split_vma(mm, vma, start, 1);
 192                if (error)
 193                        goto fail;
 194        }
 195
 196        if (end != vma->vm_end) {
 197                error = split_vma(mm, vma, end, 0);
 198                if (error)
 199                        goto fail;
 200        }
 201
 202success:
 203        /*
 204         * vm_flags and vm_page_prot are protected by the mmap_sem
 205         * held in write mode.
 206         */
 207        vma->vm_flags = newflags;
 208        vma->vm_page_prot = pgprot_modify(vma->vm_page_prot,
 209                                          vm_get_page_prot(newflags));
 210
 211        if (vma_wants_writenotify(vma)) {
 212                vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
 213                dirty_accountable = 1;
 214        }
 215
 216        mmu_notifier_invalidate_range_start(mm, start, end);
 217        if (is_vm_hugetlb_page(vma))
 218                hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
 219        else
 220                change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
 221        mmu_notifier_invalidate_range_end(mm, start, end);
 222        vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
 223        vm_stat_account(mm, newflags, vma->vm_file, nrpages);
 224        perf_event_mmap(vma);
 225        return 0;
 226
 227fail:
 228        vm_unacct_memory(charged);
 229        return error;
 230}
 231
 232SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
 233                unsigned long, prot)
 234{
 235        unsigned long vm_flags, nstart, end, tmp, reqprot;
 236        struct vm_area_struct *vma, *prev;
 237        int error = -EINVAL;
 238        const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
 239        prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
 240        if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
 241                return -EINVAL;
 242
 243        if (start & ~PAGE_MASK)
 244                return -EINVAL;
 245        if (!len)
 246                return 0;
 247        len = PAGE_ALIGN(len);
 248        end = start + len;
 249        if (end <= start)
 250                return -ENOMEM;
 251        if (!arch_validate_prot(prot))
 252                return -EINVAL;
 253
 254        reqprot = prot;
 255        /*
 256         * Does the application expect PROT_READ to imply PROT_EXEC:
 257         */
 258        if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
 259                prot |= PROT_EXEC;
 260
 261        vm_flags = calc_vm_prot_bits(prot);
 262
 263        down_write(&current->mm->mmap_sem);
 264
 265        vma = find_vma_prev(current->mm, start, &prev);
 266        error = -ENOMEM;
 267        if (!vma)
 268                goto out;
 269        if (unlikely(grows & PROT_GROWSDOWN)) {
 270                if (vma->vm_start >= end)
 271                        goto out;
 272                start = vma->vm_start;
 273                error = -EINVAL;
 274                if (!(vma->vm_flags & VM_GROWSDOWN))
 275                        goto out;
 276        }
 277        else {
 278                if (vma->vm_start > start)
 279                        goto out;
 280                if (unlikely(grows & PROT_GROWSUP)) {
 281                        end = vma->vm_end;
 282                        error = -EINVAL;
 283                        if (!(vma->vm_flags & VM_GROWSUP))
 284                                goto out;
 285                }
 286        }
 287        if (start > vma->vm_start)
 288                prev = vma;
 289
 290        for (nstart = start ; ; ) {
 291                unsigned long newflags;
 292
 293                /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
 294
 295                newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
 296
 297                /* newflags >> 4 shift VM_MAY% in place of VM_% */
 298                if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
 299                        error = -EACCES;
 300                        goto out;
 301                }
 302
 303                error = security_file_mprotect(vma, reqprot, prot);
 304                if (error)
 305                        goto out;
 306
 307                tmp = vma->vm_end;
 308                if (tmp > end)
 309                        tmp = end;
 310                error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
 311                if (error)
 312                        goto out;
 313                nstart = tmp;
 314
 315                if (nstart < prev->vm_end)
 316                        nstart = prev->vm_end;
 317                if (nstart >= end)
 318                        goto out;
 319
 320                vma = prev->vm_next;
 321                if (!vma || vma->vm_start != nstart) {
 322                        error = -ENOMEM;
 323                        goto out;
 324                }
 325        }
 326out:
 327        up_write(&current->mm->mmap_sem);
 328        return error;
 329}
 330
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