mprotect.c revision 6606c3e0da5360799e07ae24b05080cc85c68e72 
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@redhat.com>
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/slab.h>
14#include <linux/shm.h>
15#include <linux/mman.h>
16#include <linux/fs.h>
17#include <linux/highmem.h>
18#include <linux/security.h>
19#include <linux/mempolicy.h>
20#include <linux/personality.h>
21#include <linux/syscalls.h>
22#include <linux/swap.h>
23#include <linux/swapops.h>
24#include <asm/uaccess.h>
25#include <asm/pgtable.h>
26#include <asm/cacheflush.h>
27#include <asm/tlbflush.h>
28
29static void change_pte_range(struct mm_struct *mm, pmd_t *pmd,
30		unsigned long addr, unsigned long end, pgprot_t newprot,
31		int dirty_accountable)
32{
33	pte_t *pte, oldpte;
34	spinlock_t *ptl;
35
36	pte = pte_offset_map_lock(mm, pmd, addr, &ptl);
37	arch_enter_lazy_mmu_mode();
38	do {
39		oldpte = *pte;
40		if (pte_present(oldpte)) {
41			pte_t ptent;
42
43			/* Avoid an SMP race with hardware updated dirty/clean
44			 * bits by wiping the pte and then setting the new pte
45			 * into place.
46			 */
47			ptent = ptep_get_and_clear(mm, addr, pte);
48			ptent = pte_modify(ptent, newprot);
49			/*
50			 * Avoid taking write faults for pages we know to be
51			 * dirty.
52			 */
53			if (dirty_accountable && pte_dirty(ptent))
54				ptent = pte_mkwrite(ptent);
55			set_pte_at(mm, addr, pte, ptent);
56			lazy_mmu_prot_update(ptent);
57#ifdef CONFIG_MIGRATION
58		} else if (!pte_file(oldpte)) {
59			swp_entry_t entry = pte_to_swp_entry(oldpte);
60
61			if (is_write_migration_entry(entry)) {
62				/*
63				 * A protection check is difficult so
64				 * just be safe and disable write
65				 */
66				make_migration_entry_read(&entry);
67				set_pte_at(mm, addr, pte,
68					swp_entry_to_pte(entry));
69			}
70#endif
71		}
72
73	} while (pte++, addr += PAGE_SIZE, addr != end);
74	arch_leave_lazy_mmu_mode();
75	pte_unmap_unlock(pte - 1, ptl);
76}
77
78static inline void change_pmd_range(struct mm_struct *mm, pud_t *pud,
79		unsigned long addr, unsigned long end, pgprot_t newprot,
80		int dirty_accountable)
81{
82	pmd_t *pmd;
83	unsigned long next;
84
85	pmd = pmd_offset(pud, addr);
86	do {
87		next = pmd_addr_end(addr, end);
88		if (pmd_none_or_clear_bad(pmd))
89			continue;
90		change_pte_range(mm, pmd, addr, next, newprot, dirty_accountable);
91	} while (pmd++, addr = next, addr != end);
92}
93
94static inline void change_pud_range(struct mm_struct *mm, pgd_t *pgd,
95		unsigned long addr, unsigned long end, pgprot_t newprot,
96		int dirty_accountable)
97{
98	pud_t *pud;
99	unsigned long next;
100
101	pud = pud_offset(pgd, addr);
102	do {
103		next = pud_addr_end(addr, end);
104		if (pud_none_or_clear_bad(pud))
105			continue;
106		change_pmd_range(mm, pud, addr, next, newprot, dirty_accountable);
107	} while (pud++, addr = next, addr != end);
108}
109
110static void change_protection(struct vm_area_struct *vma,
111		unsigned long addr, unsigned long end, pgprot_t newprot,
112		int dirty_accountable)
113{
114	struct mm_struct *mm = vma->vm_mm;
115	pgd_t *pgd;
116	unsigned long next;
117	unsigned long start = addr;
118
119	BUG_ON(addr >= end);
120	pgd = pgd_offset(mm, addr);
121	flush_cache_range(vma, addr, end);
122	do {
123		next = pgd_addr_end(addr, end);
124		if (pgd_none_or_clear_bad(pgd))
125			continue;
126		change_pud_range(mm, pgd, addr, next, newprot, dirty_accountable);
127	} while (pgd++, addr = next, addr != end);
128	flush_tlb_range(vma, start, end);
129}
130
131static int
132mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
133	unsigned long start, unsigned long end, unsigned long newflags)
134{
135	struct mm_struct *mm = vma->vm_mm;
136	unsigned long oldflags = vma->vm_flags;
137	long nrpages = (end - start) >> PAGE_SHIFT;
138	unsigned long charged = 0;
139	pgoff_t pgoff;
140	int error;
141	int dirty_accountable = 0;
142
143	if (newflags == oldflags) {
144		*pprev = vma;
145		return 0;
146	}
147
148	/*
149	 * If we make a private mapping writable we increase our commit;
150	 * but (without finer accounting) cannot reduce our commit if we
151	 * make it unwritable again.
152	 *
153	 * FIXME? We haven't defined a VM_NORESERVE flag, so mprotecting
154	 * a MAP_NORESERVE private mapping to writable will now reserve.
155	 */
156	if (newflags & VM_WRITE) {
157		if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_SHARED))) {
158			charged = nrpages;
159			if (security_vm_enough_memory(charged))
160				return -ENOMEM;
161			newflags |= VM_ACCOUNT;
162		}
163	}
164
165	/*
166	 * First try to merge with previous and/or next vma.
167	 */
168	pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
169	*pprev = vma_merge(mm, *pprev, start, end, newflags,
170			vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
171	if (*pprev) {
172		vma = *pprev;
173		goto success;
174	}
175
176	*pprev = vma;
177
178	if (start != vma->vm_start) {
179		error = split_vma(mm, vma, start, 1);
180		if (error)
181			goto fail;
182	}
183
184	if (end != vma->vm_end) {
185		error = split_vma(mm, vma, end, 0);
186		if (error)
187			goto fail;
188	}
189
190success:
191	/*
192	 * vm_flags and vm_page_prot are protected by the mmap_sem
193	 * held in write mode.
194	 */
195	vma->vm_flags = newflags;
196	vma->vm_page_prot = protection_map[newflags &
197		(VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)];
198	if (vma_wants_writenotify(vma)) {
199		vma->vm_page_prot = protection_map[newflags &
200			(VM_READ|VM_WRITE|VM_EXEC)];
201		dirty_accountable = 1;
202	}
203
204	if (is_vm_hugetlb_page(vma))
205		hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
206	else
207		change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
208	vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
209	vm_stat_account(mm, newflags, vma->vm_file, nrpages);
210	return 0;
211
212fail:
213	vm_unacct_memory(charged);
214	return error;
215}
216
217asmlinkage long
218sys_mprotect(unsigned long start, size_t len, unsigned long prot)
219{
220	unsigned long vm_flags, nstart, end, tmp, reqprot;
221	struct vm_area_struct *vma, *prev;
222	int error = -EINVAL;
223	const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
224	prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
225	if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
226		return -EINVAL;
227
228	if (start & ~PAGE_MASK)
229		return -EINVAL;
230	if (!len)
231		return 0;
232	len = PAGE_ALIGN(len);
233	end = start + len;
234	if (end <= start)
235		return -ENOMEM;
236	if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM))
237		return -EINVAL;
238
239	reqprot = prot;
240	/*
241	 * Does the application expect PROT_READ to imply PROT_EXEC:
242	 */
243	if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
244		prot |= PROT_EXEC;
245
246	vm_flags = calc_vm_prot_bits(prot);
247
248	down_write(&current->mm->mmap_sem);
249
250	vma = find_vma_prev(current->mm, start, &prev);
251	error = -ENOMEM;
252	if (!vma)
253		goto out;
254	if (unlikely(grows & PROT_GROWSDOWN)) {
255		if (vma->vm_start >= end)
256			goto out;
257		start = vma->vm_start;
258		error = -EINVAL;
259		if (!(vma->vm_flags & VM_GROWSDOWN))
260			goto out;
261	}
262	else {
263		if (vma->vm_start > start)
264			goto out;
265		if (unlikely(grows & PROT_GROWSUP)) {
266			end = vma->vm_end;
267			error = -EINVAL;
268			if (!(vma->vm_flags & VM_GROWSUP))
269				goto out;
270		}
271	}
272	if (start > vma->vm_start)
273		prev = vma;
274
275	for (nstart = start ; ; ) {
276		unsigned long newflags;
277
278		/* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
279
280		newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
281
282		/* newflags >> 4 shift VM_MAY% in place of VM_% */
283		if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
284			error = -EACCES;
285			goto out;
286		}
287
288		error = security_file_mprotect(vma, reqprot, prot);
289		if (error)
290			goto out;
291
292		tmp = vma->vm_end;
293		if (tmp > end)
294			tmp = end;
295		error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
296		if (error)
297			goto out;
298		nstart = tmp;
299
300		if (nstart < prev->vm_end)
301			nstart = prev->vm_end;
302		if (nstart >= end)
303			goto out;
304
305		vma = prev->vm_next;
306		if (!vma || vma->vm_start != nstart) {
307			error = -ENOMEM;
308			goto out;
309		}
310	}
311out:
312	up_write(&current->mm->mmap_sem);
313	return error;
314}
315