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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/pkeys.h>
 27 #include <linux/ksm.h>
 28 #include <linux/uaccess.h>
 29 #include <asm/pgtable.h>
 30 #include <asm/cacheflush.h>
 31 #include <asm/mmu_context.h>
 32 #include <asm/tlbflush.h>
 33 
 34 #include "internal.h"
 35 
 36 /*
 37  * For a prot_numa update we only hold mmap_sem for read so there is a
 38  * potential race with faulting where a pmd was temporarily none. This
 39  * function checks for a transhuge pmd under the appropriate lock. It
 40  * returns a pte if it was successfully locked or NULL if it raced with
 41  * a transhuge insertion.
 42  */
 43 static pte_t *lock_pte_protection(struct vm_area_struct *vma, pmd_t *pmd,
 44                         unsigned long addr, int prot_numa, spinlock_t **ptl)
 45 {
 46         pte_t *pte;
 47         spinlock_t *pmdl;
 48 
 49         /* !prot_numa is protected by mmap_sem held for write */
 50         if (!prot_numa)
 51                 return pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
 52 
 53         pmdl = pmd_lock(vma->vm_mm, pmd);
 54         if (unlikely(pmd_trans_huge(*pmd) || pmd_none(*pmd))) {
 55                 spin_unlock(pmdl);
 56                 return NULL;
 57         }
 58 
 59         pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, ptl);
 60         spin_unlock(pmdl);
 61         return pte;
 62 }
 63 
 64 static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 65                 unsigned long addr, unsigned long end, pgprot_t newprot,
 66                 int dirty_accountable, int prot_numa)
 67 {
 68         struct mm_struct *mm = vma->vm_mm;
 69         pte_t *pte, oldpte;
 70         spinlock_t *ptl;
 71         unsigned long pages = 0;
 72         int target_node = NUMA_NO_NODE;
 73 
 74         pte = lock_pte_protection(vma, pmd, addr, prot_numa, &ptl);
 75         if (!pte)
 76                 return 0;
 77 
 78         /* Get target node for single threaded private VMAs */
 79         if (prot_numa && !(vma->vm_flags & VM_SHARED) &&
 80             atomic_read(&vma->vm_mm->mm_users) == 1)
 81                 target_node = numa_node_id();
 82 
 83         arch_enter_lazy_mmu_mode();
 84         do {
 85                 oldpte = *pte;
 86                 if (pte_present(oldpte)) {
 87                         pte_t ptent;
 88                         bool preserve_write = prot_numa && pte_write(oldpte);
 89 
 90                         /*
 91                          * Avoid trapping faults against the zero or KSM
 92                          * pages. See similar comment in change_huge_pmd.
 93                          */
 94                         if (prot_numa) {
 95                                 struct page *page;
 96 
 97                                 page = vm_normal_page(vma, addr, oldpte);
 98                                 if (!page || PageKsm(page))
 99                                         continue;
100 
101                                 /* Avoid TLB flush if possible */
102                                 if (pte_protnone(oldpte))
103                                         continue;
104 
105                                 /*
106                                  * Don't mess with PTEs if page is already on the node
107                                  * a single-threaded process is running on.
108                                  */
109                                 if (target_node == page_to_nid(page))
110                                         continue;
111                         }
112 
113                         ptent = ptep_modify_prot_start(mm, addr, pte);
114                         ptent = pte_modify(ptent, newprot);
115                         if (preserve_write)
116                                 ptent = pte_mkwrite(ptent);
117 
118                         /* Avoid taking write faults for known dirty pages */
119                         if (dirty_accountable && pte_dirty(ptent) &&
120                                         (pte_soft_dirty(ptent) ||
121                                          !(vma->vm_flags & VM_SOFTDIRTY))) {
122                                 ptent = pte_mkwrite(ptent);
123                         }
124                         ptep_modify_prot_commit(mm, addr, pte, ptent);
125                         pages++;
126                 } else if (IS_ENABLED(CONFIG_MIGRATION)) {
127                         swp_entry_t entry = pte_to_swp_entry(oldpte);
128 
129                         if (is_write_migration_entry(entry)) {
130                                 pte_t newpte;
131                                 /*
132                                  * A protection check is difficult so
133                                  * just be safe and disable write
134                                  */
135                                 make_migration_entry_read(&entry);
136                                 newpte = swp_entry_to_pte(entry);
137                                 if (pte_swp_soft_dirty(oldpte))
138                                         newpte = pte_swp_mksoft_dirty(newpte);
139                                 set_pte_at(mm, addr, pte, newpte);
140 
141                                 pages++;
142                         }
143                 }
144         } while (pte++, addr += PAGE_SIZE, addr != end);
145         arch_leave_lazy_mmu_mode();
146         pte_unmap_unlock(pte - 1, ptl);
147 
148         return pages;
149 }
150 
151 static inline unsigned long change_pmd_range(struct vm_area_struct *vma,
152                 pud_t *pud, unsigned long addr, unsigned long end,
153                 pgprot_t newprot, int dirty_accountable, int prot_numa)
154 {
155         pmd_t *pmd;
156         struct mm_struct *mm = vma->vm_mm;
157         unsigned long next;
158         unsigned long pages = 0;
159         unsigned long nr_huge_updates = 0;
160         unsigned long mni_start = 0;
161 
162         pmd = pmd_offset(pud, addr);
163         do {
164                 unsigned long this_pages;
165 
166                 next = pmd_addr_end(addr, end);
167                 if (!pmd_trans_huge(*pmd) && !pmd_devmap(*pmd)
168                                 && pmd_none_or_clear_bad(pmd))
169                         continue;
170 
171                 /* invoke the mmu notifier if the pmd is populated */
172                 if (!mni_start) {
173                         mni_start = addr;
174                         mmu_notifier_invalidate_range_start(mm, mni_start, end);
175                 }
176 
177                 if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) {
178                         if (next - addr != HPAGE_PMD_SIZE) {
179                                 __split_huge_pmd(vma, pmd, addr, false, NULL);
180                                 if (pmd_trans_unstable(pmd))
181                                         continue;
182                         } else {
183                                 int nr_ptes = change_huge_pmd(vma, pmd, addr,
184                                                 newprot, prot_numa);
185 
186                                 if (nr_ptes) {
187                                         if (nr_ptes == HPAGE_PMD_NR) {
188                                                 pages += HPAGE_PMD_NR;
189                                                 nr_huge_updates++;
190                                         }
191 
192                                         /* huge pmd was handled */
193                                         continue;
194                                 }
195                         }
196                         /* fall through, the trans huge pmd just split */
197                 }
198                 this_pages = change_pte_range(vma, pmd, addr, next, newprot,
199                                  dirty_accountable, prot_numa);
200                 pages += this_pages;
201         } while (pmd++, addr = next, addr != end);
202 
203         if (mni_start)
204                 mmu_notifier_invalidate_range_end(mm, mni_start, end);
205 
206         if (nr_huge_updates)
207                 count_vm_numa_events(NUMA_HUGE_PTE_UPDATES, nr_huge_updates);
208         return pages;
209 }
210 
211 static inline unsigned long change_pud_range(struct vm_area_struct *vma,
212                 pgd_t *pgd, unsigned long addr, unsigned long end,
213                 pgprot_t newprot, int dirty_accountable, int prot_numa)
214 {
215         pud_t *pud;
216         unsigned long next;
217         unsigned long pages = 0;
218 
219         pud = pud_offset(pgd, addr);
220         do {
221                 next = pud_addr_end(addr, end);
222                 if (pud_none_or_clear_bad(pud))
223                         continue;
224                 pages += change_pmd_range(vma, pud, addr, next, newprot,
225                                  dirty_accountable, prot_numa);
226         } while (pud++, addr = next, addr != end);
227 
228         return pages;
229 }
230 
231 static unsigned long change_protection_range(struct vm_area_struct *vma,
232                 unsigned long addr, unsigned long end, pgprot_t newprot,
233                 int dirty_accountable, int prot_numa)
234 {
235         struct mm_struct *mm = vma->vm_mm;
236         pgd_t *pgd;
237         unsigned long next;
238         unsigned long start = addr;
239         unsigned long pages = 0;
240 
241         BUG_ON(addr >= end);
242         pgd = pgd_offset(mm, addr);
243         flush_cache_range(vma, addr, end);
244         set_tlb_flush_pending(mm);
245         do {
246                 next = pgd_addr_end(addr, end);
247                 if (pgd_none_or_clear_bad(pgd))
248                         continue;
249                 pages += change_pud_range(vma, pgd, addr, next, newprot,
250                                  dirty_accountable, prot_numa);
251         } while (pgd++, addr = next, addr != end);
252 
253         /* Only flush the TLB if we actually modified any entries: */
254         if (pages)
255                 flush_tlb_range(vma, start, end);
256         clear_tlb_flush_pending(mm);
257 
258         return pages;
259 }
260 
261 unsigned long change_protection(struct vm_area_struct *vma, unsigned long start,
262                        unsigned long end, pgprot_t newprot,
263                        int dirty_accountable, int prot_numa)
264 {
265         unsigned long pages;
266 
267         if (is_vm_hugetlb_page(vma))
268                 pages = hugetlb_change_protection(vma, start, end, newprot);
269         else
270                 pages = change_protection_range(vma, start, end, newprot, dirty_accountable, prot_numa);
271 
272         return pages;
273 }
274 
275 int
276 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
277         unsigned long start, unsigned long end, unsigned long newflags)
278 {
279         struct mm_struct *mm = vma->vm_mm;
280         unsigned long oldflags = vma->vm_flags;
281         long nrpages = (end - start) >> PAGE_SHIFT;
282         unsigned long charged = 0;
283         pgoff_t pgoff;
284         int error;
285         int dirty_accountable = 0;
286 
287         if (newflags == oldflags) {
288                 *pprev = vma;
289                 return 0;
290         }
291 
292         /*
293          * If we make a private mapping writable we increase our commit;
294          * but (without finer accounting) cannot reduce our commit if we
295          * make it unwritable again. hugetlb mapping were accounted for
296          * even if read-only so there is no need to account for them here
297          */
298         if (newflags & VM_WRITE) {
299                 /* Check space limits when area turns into data. */
300                 if (!may_expand_vm(mm, newflags, nrpages) &&
301                                 may_expand_vm(mm, oldflags, nrpages))
302                         return -ENOMEM;
303                 if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_HUGETLB|
304                                                 VM_SHARED|VM_NORESERVE))) {
305                         charged = nrpages;
306                         if (security_vm_enough_memory_mm(mm, charged))
307                                 return -ENOMEM;
308                         newflags |= VM_ACCOUNT;
309                 }
310         }
311 
312         /*
313          * First try to merge with previous and/or next vma.
314          */
315         pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
316         *pprev = vma_merge(mm, *pprev, start, end, newflags,
317                            vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma),
318                            vma->vm_userfaultfd_ctx);
319         if (*pprev) {
320                 vma = *pprev;
321                 VM_WARN_ON((vma->vm_flags ^ newflags) & ~VM_SOFTDIRTY);
322                 goto success;
323         }
324 
325         *pprev = vma;
326 
327         if (start != vma->vm_start) {
328                 error = split_vma(mm, vma, start, 1);
329                 if (error)
330                         goto fail;
331         }
332 
333         if (end != vma->vm_end) {
334                 error = split_vma(mm, vma, end, 0);
335                 if (error)
336                         goto fail;
337         }
338 
339 success:
340         /*
341          * vm_flags and vm_page_prot are protected by the mmap_sem
342          * held in write mode.
343          */
344         vma->vm_flags = newflags;
345         dirty_accountable = vma_wants_writenotify(vma, vma->vm_page_prot);
346         vma_set_page_prot(vma);
347 
348         change_protection(vma, start, end, vma->vm_page_prot,
349                           dirty_accountable, 0);
350 
351         /*
352          * Private VM_LOCKED VMA becoming writable: trigger COW to avoid major
353          * fault on access.
354          */
355         if ((oldflags & (VM_WRITE | VM_SHARED | VM_LOCKED)) == VM_LOCKED &&
356                         (newflags & VM_WRITE)) {
357                 populate_vma_page_range(vma, start, end, NULL);
358         }
359 
360         vm_stat_account(mm, oldflags, -nrpages);
361         vm_stat_account(mm, newflags, nrpages);
362         perf_event_mmap(vma);
363         return 0;
364 
365 fail:
366         vm_unacct_memory(charged);
367         return error;
368 }
369 
370 /*
371  * pkey==-1 when doing a legacy mprotect()
372  */
373 static int do_mprotect_pkey(unsigned long start, size_t len,
374                 unsigned long prot, int pkey)
375 {
376         unsigned long nstart, end, tmp, reqprot;
377         struct vm_area_struct *vma, *prev;
378         int error = -EINVAL;
379         const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
380         const bool rier = (current->personality & READ_IMPLIES_EXEC) &&
381                                 (prot & PROT_READ);
382 
383         prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
384         if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
385                 return -EINVAL;
386 
387         if (start & ~PAGE_MASK)
388                 return -EINVAL;
389         if (!len)
390                 return 0;
391         len = PAGE_ALIGN(len);
392         end = start + len;
393         if (end <= start)
394                 return -ENOMEM;
395         if (!arch_validate_prot(prot))
396                 return -EINVAL;
397 
398         reqprot = prot;
399 
400         if (down_write_killable(&current->mm->mmap_sem))
401                 return -EINTR;
402 
403         /*
404          * If userspace did not allocate the pkey, do not let
405          * them use it here.
406          */
407         error = -EINVAL;
408         if ((pkey != -1) && !mm_pkey_is_allocated(current->mm, pkey))
409                 goto out;
410 
411         vma = find_vma(current->mm, start);
412         error = -ENOMEM;
413         if (!vma)
414                 goto out;
415         prev = vma->vm_prev;
416         if (unlikely(grows & PROT_GROWSDOWN)) {
417                 if (vma->vm_start >= end)
418                         goto out;
419                 start = vma->vm_start;
420                 error = -EINVAL;
421                 if (!(vma->vm_flags & VM_GROWSDOWN))
422                         goto out;
423         } else {
424                 if (vma->vm_start > start)
425                         goto out;
426                 if (unlikely(grows & PROT_GROWSUP)) {
427                         end = vma->vm_end;
428                         error = -EINVAL;
429                         if (!(vma->vm_flags & VM_GROWSUP))
430                                 goto out;
431                 }
432         }
433         if (start > vma->vm_start)
434                 prev = vma;
435 
436         for (nstart = start ; ; ) {
437                 unsigned long mask_off_old_flags;
438                 unsigned long newflags;
439                 int new_vma_pkey;
440 
441                 /* Here we know that vma->vm_start <= nstart < vma->vm_end. */
442 
443                 /* Does the application expect PROT_READ to imply PROT_EXEC */
444                 if (rier && (vma->vm_flags & VM_MAYEXEC))
445                         prot |= PROT_EXEC;
446 
447                 /*
448                  * Each mprotect() call explicitly passes r/w/x permissions.
449                  * If a permission is not passed to mprotect(), it must be
450                  * cleared from the VMA.
451                  */
452                 mask_off_old_flags = VM_READ | VM_WRITE | VM_EXEC |
453                                         ARCH_VM_PKEY_FLAGS;
454 
455                 new_vma_pkey = arch_override_mprotect_pkey(vma, prot, pkey);
456                 newflags = calc_vm_prot_bits(prot, new_vma_pkey);
457                 newflags |= (vma->vm_flags & ~mask_off_old_flags);
458 
459                 /* newflags >> 4 shift VM_MAY% in place of VM_% */
460                 if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
461                         error = -EACCES;
462                         goto out;
463                 }
464 
465                 error = security_file_mprotect(vma, reqprot, prot);
466                 if (error)
467                         goto out;
468 
469                 tmp = vma->vm_end;
470                 if (tmp > end)
471                         tmp = end;
472                 error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
473                 if (error)
474                         goto out;
475                 nstart = tmp;
476 
477                 if (nstart < prev->vm_end)
478                         nstart = prev->vm_end;
479                 if (nstart >= end)
480                         goto out;
481 
482                 vma = prev->vm_next;
483                 if (!vma || vma->vm_start != nstart) {
484                         error = -ENOMEM;
485                         goto out;
486                 }
487                 prot = reqprot;
488         }
489 out:
490         up_write(&current->mm->mmap_sem);
491         return error;
492 }
493 
494 SYSCALL_DEFINE3(mprotect, unsigned long, start, size_t, len,
495                 unsigned long, prot)
496 {
497         return do_mprotect_pkey(start, len, prot, -1);
498 }
499 
500 #ifdef CONFIG_ARCH_HAS_PKEYS
501 
502 SYSCALL_DEFINE4(pkey_mprotect, unsigned long, start, size_t, len,
503                 unsigned long, prot, int, pkey)
504 {
505         return do_mprotect_pkey(start, len, prot, pkey);
506 }
507 
508 SYSCALL_DEFINE2(pkey_alloc, unsigned long, flags, unsigned long, init_val)
509 {
510         int pkey;
511         int ret;
512 
513         /* No flags supported yet. */
514         if (flags)
515                 return -EINVAL;
516         /* check for unsupported init values */
517         if (init_val & ~PKEY_ACCESS_MASK)
518                 return -EINVAL;
519 
520         down_write(&current->mm->mmap_sem);
521         pkey = mm_pkey_alloc(current->mm);
522 
523         ret = -ENOSPC;
524         if (pkey == -1)
525                 goto out;
526 
527         ret = arch_set_user_pkey_access(current, pkey, init_val);
528         if (ret) {
529                 mm_pkey_free(current->mm, pkey);
530                 goto out;
531         }
532         ret = pkey;
533 out:
534         up_write(&current->mm->mmap_sem);
535         return ret;
536 }
537 
538 SYSCALL_DEFINE1(pkey_free, int, pkey)
539 {
540         int ret;
541 
542         down_write(&current->mm->mmap_sem);
543         ret = mm_pkey_free(current->mm, pkey);
544         up_write(&current->mm->mmap_sem);
545 
546         /*
547          * We could provie warnings or errors if any VMA still
548          * has the pkey set here.
549          */
550         return ret;
551 }
552 
553 #endif /* CONFIG_ARCH_HAS_PKEYS */
554 

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