mprotect.c

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/*
 *  mm/mprotect.c
 *
 *  (C) Copyright 1994 Linus Torvalds
 *  (C) Copyright 2002 Christoph Hellwig
 *
 *  Address space accounting code   <[email protected]>
 *  (C) Copyright 2002 Red Hat Inc, All Rights Reserved
 */

#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/shm.h>
#include <linux/mman.h>
#include <linux/fs.h>
#include <linux/highmem.h>
#include <linux/security.h>
#include <linux/mempolicy.h>
#include <linux/personality.h>
#include <linux/syscalls.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/mmu_notifier.h>
#include <linux/migrate.h>
#include <linux/perf_event.h>
#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/cacheflush.h>
#include <asm/tlbflush.h>

#ifndef pgprot_modify
static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
{
    return newprot;
}
#endif

static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
        unsigned long addr, unsigned long end, pgprot_t newprot,
        int dirty_accountable)
{
    pte_t *pte, oldpte;
    spinlock_t *ptl;

    pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
    arch_enter_lazy_mmu_mode();
    do {
        oldpte = *pte;
        if (pte_present(oldpte)) {
            pte_t ptent;

            ptent = ptep_modify_prot_start(mm, addr, pte);
            ptent = pte_modify(ptent, newprot);

            /*
             * Avoid taking write faults for pages we know to be
             * dirty.
             */
            if (dirty_accountable && pte_dirty(ptent))
                ptent = pte_mkwrite(ptent);

            ptep_modify_prot_commit(mm, addr, pte, ptent);
        } else if (IS_ENABLED(CONFIG_MIGRATION) && !pte_file(oldpte)) {
            swp_entry_t entry = pte_to_swp_entry(oldpte);

            if (is_write_migration_entry(entry)) {
                /*
                 * A protection check is difficult so
                 * just be safe and disable write
                 */
                make_migration_entry_read(&entry);
                set_pte_at(mm, addr, pte,
                    swp_entry_to_pte(entry));
            }
        }
    } while (pte++, addr += PAGE_SIZE, addr != end);
    arch_leave_lazy_mmu_mode();
    pte_unmap_unlock(pte - 1, ptl);
}

static inline void change_pmd_range(struct vm_area_struct *vma, pud_t *pud,
        unsigned long addr, unsigned long end, pgprot_t newprot,
        int dirty_accountable)
{
    pmd_t *pmd;
    unsigned long next;

    pmd = pmd_offset(pud, addr);
    do {
        next = pmd_addr_end(addr, end);
        if (pmd_trans_huge(*pmd)) {
            if (next - addr != HPAGE_PMD_SIZE)
                split_huge_page_pmd(vma->vm_mm, pmd);
            else if (change_huge_pmd(vma, pmd, addr, newprot))
                continue;
            /* fall through */
        }
        if (pmd_none_or_clear_bad(pmd))
            continue;
        change_pte_range(vma->vm_mm, pmd, addr, next, newprot,
                 dirty_accountable);
    } while (pmd++, addr = next, addr != end);
}

static inline void change_pud_range(struct vm_area_struct *vma, pgd_t *pgd,
        unsigned long addr, unsigned long end, pgprot_t newprot,
        int dirty_accountable)
{
    pud_t *pud;
    unsigned long next;

    pud = pud_offset(pgd, addr);
    do {
        next = pud_addr_end(addr, end);
        if (pud_none_or_clear_bad(pud))
            continue;
        change_pmd_range(vma, pud, addr, next, newprot,
                 dirty_accountable);
    } while (pud++, addr = next, addr != end);
}

static void change_protection(struct vm_area_struct *vma,
        unsigned long addr, unsigned long end, pgprot_t newprot,
        int dirty_accountable)
{
    struct mm_struct *mm = vma->vm_mm;
    pgd_t *pgd;
    unsigned long next;
    unsigned long start = addr;

    BUG_ON(addr >= end);
    pgd = pgd_offset(mm, addr);
    flush_cache_range(vma, addr, end);
    do {
        next = pgd_addr_end(addr, end);
        if (pgd_none_or_clear_bad(pgd))
            continue;
        change_pud_range(vma, pgd, addr, next, newprot,
                 dirty_accountable);
    } while (pgd++, addr = next, addr != end);
    flush_tlb_range(vma, start, end);
}

int
mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
    unsigned long start, unsigned long end, unsigned long newflags)
{
    struct mm_struct *mm = vma->vm_mm;
    unsigned long oldflags = vma->vm_flags;
    long nrpages = (end - start) >> PAGE_SHIFT;
    unsigned long charged = 0;
    pgoff_t pgoff;
    int error;
    int dirty_accountable = 0;

    if (newflags == oldflags) {
        *pprev = vma;
        return 0;
    }

    /*
     * If we make a private mapping writable we increase our commit;
     * but (without finer accounting) cannot reduce our commit if we
     * make it unwritable again. hugetlb mapping were accounted for
     * even if read-only so there is no need to account for them here
     */
    if (newflags & VM_WRITE) {
        if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
                        VM_SHARED|VM_NORESERVE))) {
            charged = nrpages;
            if (security_vm_enough_memory_mm(mm, charged))
                return -ENOMEM;
            newflags |= VM_ACCOUNT;
        }
    }

    /*
     * First try to merge with previous and/or next vma.
     */
    pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
    *pprev = vma_merge(mm, *pprev, start, end, newflags,
            vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
    if (*pprev) {
        vma = *pprev;
        goto success;
    }

    *pprev = vma;

    if (start != vma->vm_start) {
        error = split_vma(mm, vma, start, 1);
        if (error)
            goto fail;
    }

    if (end != vma->vm_end) {
        error = split_vma(mm, vma, end, 0);
        if (error)
            goto fail;
    }

success:
    /*
     * vm_flags and vm_page_prot are protected by the mmap_sem
     * held in write mode.
     */
    vma->vm_flags = newflags;
    vma->vm_page_prot = pgprot_modify(vma->vm_page_prot,
                      vm_get_page_prot(newflags));

    if (vma_wants_writenotify(vma)) {
        vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
        dirty_accountable = 1;
    }

    mmu_notifier_invalidate_range_start(mm, start, end);
    if (is_vm_hugetlb_page(vma))
        hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
    else
        change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
    mmu_notifier_invalidate_range_end(mm, start, end);
    vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
    vm_stat_account(mm, newflags, vma->vm_file, nrpages);
    perf_event_mmap(vma);
    return 0;

fail:
    vm_unacct_memory(charged);
    return error;
}

SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
        unsigned long, prot)
{
    unsigned long vm_flags, nstart, end, tmp, reqprot;
    struct vm_area_struct *vma, *prev;
    int error = -EINVAL;
    const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
    prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
    if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
        return -EINVAL;

    if (start & ~PAGE_MASK)
        return -EINVAL;
    if (!len)
        return 0;
    len = PAGE_ALIGN(len);
    end = start + len;
    if (end <= start)
        return -ENOMEM;
    if (!arch_validate_prot(prot))
        return -EINVAL;

    reqprot = prot;
    /*
     * Does the application expect PROT_READ to imply PROT_EXEC:
     */
    if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
        prot |= PROT_EXEC;

    vm_flags = calc_vm_prot_bits(prot);

    down_write(&current->mm->mmap_sem);

    vma = find_vma(current->mm, start);
    error = -ENOMEM;
    if (!vma)
        goto out;
    prev = vma->vm_prev;
    if (unlikely(grows & PROT_GROWSDOWN)) {
        if (vma->vm_start >= end)
            goto out;
        start = vma->vm_start;
        error = -EINVAL;
        if (!(vma->vm_flags & VM_GROWSDOWN))
            goto out;
    }
    else {
        if (vma->vm_start > start)
            goto out;
        if (unlikely(grows & PROT_GROWSUP)) {
            end = vma->vm_end;
            error = -EINVAL;
            if (!(vma->vm_flags & VM_GROWSUP))
                goto out;
        }
    }
    if (start > vma->vm_start)
        prev = vma;

    for (nstart = start ; ; ) {
        unsigned long newflags;

        /* Here we know that  vma->vm_start <= nstart < vma->vm_end. */

        newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));

        /* newflags >> 4 shift VM_MAY% in place of VM_% */
        if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
            error = -EACCES;
            goto out;
        }

        error = security_file_mprotect(vma, reqprot, prot);
        if (error)
            goto out;

        tmp = vma->vm_end;
        if (tmp > end)
            tmp = end;
        error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
        if (error)
            goto out;
        nstart = tmp;

        if (nstart < prev->vm_end)
            nstart = prev->vm_end;
        if (nstart >= end)
            goto out;

        vma = prev->vm_next;
        if (!vma || vma->vm_start != nstart) {
            error = -ENOMEM;
            goto out;
        }
    }
out:
    up_write(&current->mm->mmap_sem);
    return error;
}