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 <linux/ksm.h>
27#include <asm/uaccess.h>
28#include <asm/pgtable.h>
29#include <asm/cacheflush.h>
30#include <asm/tlbflush.h>
31
32#ifndef pgprot_modify
33static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
34{
35    return newprot;
36}
37#endif
38
39/*
40 * For a prot_numa update we only hold mmap_sem for read so there is a
41 * potential race with faulting where a pmd was temporarily none. This
42 * function checks for a transhuge pmd under the appropriate lock. It
43 * returns a pte if it was successfully locked or NULL if it raced with
44 * a transhuge insertion.
45 */
46static pte_t *lock_pte_protection(struct vm_area_struct *vma, pmd_t *pmd,
47            unsigned long addr, int prot_numa, spinlock_t **ptl)
48{
49    pte_t *pte;
50    spinlock_t *pmdl;
51
52    /* !prot_numa is protected by mmap_sem held for write */
53    if (!prot_numa)
54        return pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
55
56    pmdl = pmd_lock(vma->vm_mm, pmd);
57    if (unlikely(pmd_trans_huge(*pmd) || pmd_none(*pmd))) {
58        spin_unlock(pmdl);
59        return NULL;
60    }
61
62    pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
63    spin_unlock(pmdl);
64    return pte;
65}
66
67static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
68        unsigned long addr, unsigned long end, pgprot_t newprot,
69        int dirty_accountable, int prot_numa)
70{
71    struct mm_struct *mm = vma->vm_mm;
72    pte_t *pte, oldpte;
73    spinlock_t *ptl;
74    unsigned long pages = 0;
75
76    pte = lock_pte_protection(vma, pmd, addr, prot_numa, &ptl);
77    if (!pte)
78        return 0;
79
80    arch_enter_lazy_mmu_mode();
81    do {
82        oldpte = *pte;
83        if (pte_present(oldpte)) {
84            pte_t ptent;
85            bool updated = false;
86
87            if (!prot_numa) {
88                ptent = ptep_modify_prot_start(mm, addr, pte);
89                if (pte_numa(ptent))
90                    ptent = pte_mknonnuma(ptent);
91                ptent = pte_modify(ptent, newprot);
92                /*
93                 * Avoid taking write faults for pages we
94                 * know to be dirty.
95                 */
96                if (dirty_accountable && pte_dirty(ptent))
97                    ptent = pte_mkwrite(ptent);
98                ptep_modify_prot_commit(mm, addr, pte, ptent);
99                updated = true;
100            } else {
101                struct page *page;
102
103                page = vm_normal_page(vma, addr, oldpte);
104                if (page && !PageKsm(page)) {
105                    if (!pte_numa(oldpte)) {
106                        ptep_set_numa(mm, addr, pte);
107                        updated = true;
108                    }
109                }
110            }
111            if (updated)
112                pages++;
113        } else if (IS_ENABLED(CONFIG_MIGRATION) && !pte_file(oldpte)) {
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_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)) {
164            if (next - addr != HPAGE_PMD_SIZE)
165                split_huge_page_pmd(vma, addr, pmd);
166            else {
167                int nr_ptes = change_huge_pmd(vma, pmd, addr,
168                        newprot, prot_numa);
169
170                if (nr_ptes) {
171                    if (nr_ptes == HPAGE_PMD_NR) {
172                        pages += HPAGE_PMD_NR;
173                        nr_huge_updates++;
174                    }
175
176                    /* huge pmd was handled */
177                    continue;
178                }
179            }
180            /* fall through, the trans huge pmd just split */
181        }
182        this_pages = change_pte_range(vma, pmd, addr, next, newprot,
183                 dirty_accountable, prot_numa);
184        pages += this_pages;
185    } while (pmd++, addr = next, addr != end);
186
187    if (mni_start)
188        mmu_notifier_invalidate_range_end(mm, mni_start, end);
189
190    if (nr_huge_updates)
191        count_vm_numa_events(NUMA_HUGE_PTE_UPDATES, nr_huge_updates);
192    return pages;
193}
194
195static inline unsigned long change_pud_range(struct vm_area_struct *vma,
196        pgd_t *pgd, unsigned long addr, unsigned long end,
197        pgprot_t newprot, int dirty_accountable, int prot_numa)
198{
199    pud_t *pud;
200    unsigned long next;
201    unsigned long pages = 0;
202
203    pud = pud_offset(pgd, addr);
204    do {
205        next = pud_addr_end(addr, end);
206        if (pud_none_or_clear_bad(pud))
207            continue;
208        pages += change_pmd_range(vma, pud, addr, next, newprot,
209                 dirty_accountable, prot_numa);
210    } while (pud++, addr = next, addr != end);
211
212    return pages;
213}
214
215static unsigned long change_protection_range(struct vm_area_struct *vma,
216        unsigned long addr, unsigned long end, pgprot_t newprot,
217        int dirty_accountable, int prot_numa)
218{
219    struct mm_struct *mm = vma->vm_mm;
220    pgd_t *pgd;
221    unsigned long next;
222    unsigned long start = addr;
223    unsigned long pages = 0;
224
225    BUG_ON(addr >= end);
226    pgd = pgd_offset(mm, addr);
227    flush_cache_range(vma, addr, end);
228    set_tlb_flush_pending(mm);
229    do {
230        next = pgd_addr_end(addr, end);
231        if (pgd_none_or_clear_bad(pgd))
232            continue;
233        pages += change_pud_range(vma, pgd, addr, next, newprot,
234                 dirty_accountable, prot_numa);
235    } while (pgd++, addr = next, addr != end);
236
237    /* Only flush the TLB if we actually modified any entries: */
238    if (pages)
239        flush_tlb_range(vma, start, end);
240    clear_tlb_flush_pending(mm);
241
242    return pages;
243}
244
245unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
246               unsigned long end, pgprot_t newprot,
247               int dirty_accountable, int prot_numa)
248{
249    unsigned long pages;
250
251    if (is_vm_hugetlb_page(vma))
252        pages = hugetlb_change_protection(vma, start, end, newprot);
253    else
254        pages = change_protection_range(vma, start, end, newprot, dirty_accountable, prot_numa);
255
256    return pages;
257}
258
259int
260mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
261    unsigned long start, unsigned long end, unsigned long newflags)
262{
263    struct mm_struct *mm = vma->vm_mm;
264    unsigned long oldflags = vma->vm_flags;
265    long nrpages = (end - start) >> PAGE_SHIFT;
266    unsigned long charged = 0;
267    pgoff_t pgoff;
268    int error;
269    int dirty_accountable = 0;
270
271    if (newflags == oldflags) {
272        *pprev = vma;
273        return 0;
274    }
275
276    /*
277     * If we make a private mapping writable we increase our commit;
278     * but (without finer accounting) cannot reduce our commit if we
279     * make it unwritable again. hugetlb mapping were accounted for
280     * even if read-only so there is no need to account for them here
281     */
282    if (newflags & VM_WRITE) {
283        if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
284                        VM_SHARED|VM_NORESERVE))) {
285            charged = nrpages;
286            if (security_vm_enough_memory_mm(mm, charged))
287                return -ENOMEM;
288            newflags |= VM_ACCOUNT;
289        }
290    }
291
292    /*
293     * First try to merge with previous and/or next vma.
294     */
295    pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
296    *pprev = vma_merge(mm, *pprev, start, end, newflags,
297            vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
298    if (*pprev) {
299        vma = *pprev;
300        goto success;
301    }
302
303    *pprev = vma;
304
305    if (start != vma->vm_start) {
306        error = split_vma(mm, vma, start, 1);
307        if (error)
308            goto fail;
309    }
310
311    if (end != vma->vm_end) {
312        error = split_vma(mm, vma, end, 0);
313        if (error)
314            goto fail;
315    }
316
317success:
318    /*
319     * vm_flags and vm_page_prot are protected by the mmap_sem
320     * held in write mode.
321     */
322    vma->vm_flags = newflags;
323    vma->vm_page_prot = pgprot_modify(vma->vm_page_prot,
324                      vm_get_page_prot(newflags));
325
326    if (vma_wants_writenotify(vma)) {
327        vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
328        dirty_accountable = 1;
329    }
330
331    change_protection(vma, start, end, vma->vm_page_prot,
332              dirty_accountable, 0);
333
334    vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
335    vm_stat_account(mm, newflags, vma->vm_file, nrpages);
336    perf_event_mmap(vma);
337    return 0;
338
339fail:
340    vm_unacct_memory(charged);
341    return error;
342}
343
344SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
345        unsigned long, prot)
346{
347    unsigned long vm_flags, nstart, end, tmp, reqprot;
348    struct vm_area_struct *vma, *prev;
349    int error = -EINVAL;
350    const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
351    prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
352    if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
353        return -EINVAL;
354
355    if (start & ~PAGE_MASK)
356        return -EINVAL;
357    if (!len)
358        return 0;
359    len = PAGE_ALIGN(len);
360    end = start + len;
361    if (end <= start)
362        return -ENOMEM;
363    if (!arch_validate_prot(prot))
364        return -EINVAL;
365
366    reqprot = prot;
367    /*
368     * Does the application expect PROT_READ to imply PROT_EXEC:
369     */
370    if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
371        prot |= PROT_EXEC;
372
373    vm_flags = calc_vm_prot_bits(prot);
374
375    down_write(&current->mm->mmap_sem);
376
377    vma = find_vma(current->mm, start);
378    error = -ENOMEM;
379    if (!vma)
380        goto out;
381    prev = vma->vm_prev;
382    if (unlikely(grows & PROT_GROWSDOWN)) {
383        if (vma->vm_start >= end)
384            goto out;
385        start = vma->vm_start;
386        error = -EINVAL;
387        if (!(vma->vm_flags & VM_GROWSDOWN))
388            goto out;
389    } else {
390        if (vma->vm_start > start)
391            goto out;
392        if (unlikely(grows & PROT_GROWSUP)) {
393            end = vma->vm_end;
394            error = -EINVAL;
395            if (!(vma->vm_flags & VM_GROWSUP))
396                goto out;
397        }
398    }
399    if (start > vma->vm_start)
400        prev = vma;
401
402    for (nstart = start ; ; ) {
403        unsigned long newflags;
404
405        /* Here we know that vma->vm_start <= nstart < vma->vm_end. */
406
407        newflags = vm_flags;
408        newflags |= (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
409
410        /* newflags >> 4 shift VM_MAY% in place of VM_% */
411        if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
412            error = -EACCES;
413            goto out;
414        }
415
416        error = security_file_mprotect(vma, reqprot, prot);
417        if (error)
418            goto out;
419
420        tmp = vma->vm_end;
421        if (tmp > end)
422            tmp = end;
423        error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
424        if (error)
425            goto out;
426        nstart = tmp;
427
428        if (nstart < prev->vm_end)
429            nstart = prev->vm_end;
430        if (nstart >= end)
431            goto out;
432
433        vma = prev->vm_next;
434        if (!vma || vma->vm_start != nstart) {
435            error = -ENOMEM;
436            goto out;
437        }
438    }
439out:
440    up_write(&current->mm->mmap_sem);
441    return error;
442}
443

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