Root/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 <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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