xref: /openbmc/linux/mm/mprotect.c (revision 22246614)
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 
29 static 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 #ifdef CONFIG_MIGRATION
57 		} else if (!pte_file(oldpte)) {
58 			swp_entry_t entry = pte_to_swp_entry(oldpte);
59 
60 			if (is_write_migration_entry(entry)) {
61 				/*
62 				 * A protection check is difficult so
63 				 * just be safe and disable write
64 				 */
65 				make_migration_entry_read(&entry);
66 				set_pte_at(mm, addr, pte,
67 					swp_entry_to_pte(entry));
68 			}
69 #endif
70 		}
71 
72 	} while (pte++, addr += PAGE_SIZE, addr != end);
73 	arch_leave_lazy_mmu_mode();
74 	pte_unmap_unlock(pte - 1, ptl);
75 }
76 
77 static inline void change_pmd_range(struct mm_struct *mm, pud_t *pud,
78 		unsigned long addr, unsigned long end, pgprot_t newprot,
79 		int dirty_accountable)
80 {
81 	pmd_t *pmd;
82 	unsigned long next;
83 
84 	pmd = pmd_offset(pud, addr);
85 	do {
86 		next = pmd_addr_end(addr, end);
87 		if (pmd_none_or_clear_bad(pmd))
88 			continue;
89 		change_pte_range(mm, pmd, addr, next, newprot, dirty_accountable);
90 	} while (pmd++, addr = next, addr != end);
91 }
92 
93 static inline void change_pud_range(struct mm_struct *mm, pgd_t *pgd,
94 		unsigned long addr, unsigned long end, pgprot_t newprot,
95 		int dirty_accountable)
96 {
97 	pud_t *pud;
98 	unsigned long next;
99 
100 	pud = pud_offset(pgd, addr);
101 	do {
102 		next = pud_addr_end(addr, end);
103 		if (pud_none_or_clear_bad(pud))
104 			continue;
105 		change_pmd_range(mm, pud, addr, next, newprot, dirty_accountable);
106 	} while (pud++, addr = next, addr != end);
107 }
108 
109 static void change_protection(struct vm_area_struct *vma,
110 		unsigned long addr, unsigned long end, pgprot_t newprot,
111 		int dirty_accountable)
112 {
113 	struct mm_struct *mm = vma->vm_mm;
114 	pgd_t *pgd;
115 	unsigned long next;
116 	unsigned long start = addr;
117 
118 	BUG_ON(addr >= end);
119 	pgd = pgd_offset(mm, addr);
120 	flush_cache_range(vma, addr, end);
121 	do {
122 		next = pgd_addr_end(addr, end);
123 		if (pgd_none_or_clear_bad(pgd))
124 			continue;
125 		change_pud_range(mm, pgd, addr, next, newprot, dirty_accountable);
126 	} while (pgd++, addr = next, addr != end);
127 	flush_tlb_range(vma, start, end);
128 }
129 
130 int
131 mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
132 	unsigned long start, unsigned long end, unsigned long newflags)
133 {
134 	struct mm_struct *mm = vma->vm_mm;
135 	unsigned long oldflags = vma->vm_flags;
136 	long nrpages = (end - start) >> PAGE_SHIFT;
137 	unsigned long charged = 0;
138 	pgoff_t pgoff;
139 	int error;
140 	int dirty_accountable = 0;
141 
142 	if (newflags == oldflags) {
143 		*pprev = vma;
144 		return 0;
145 	}
146 
147 	/*
148 	 * If we make a private mapping writable we increase our commit;
149 	 * but (without finer accounting) cannot reduce our commit if we
150 	 * make it unwritable again.
151 	 *
152 	 * FIXME? We haven't defined a VM_NORESERVE flag, so mprotecting
153 	 * a MAP_NORESERVE private mapping to writable will now reserve.
154 	 */
155 	if (newflags & VM_WRITE) {
156 		if (!(oldflags & (VM_ACCOUNT|VM_WRITE|VM_SHARED))) {
157 			charged = nrpages;
158 			if (security_vm_enough_memory(charged))
159 				return -ENOMEM;
160 			newflags |= VM_ACCOUNT;
161 		}
162 	}
163 
164 	/*
165 	 * First try to merge with previous and/or next vma.
166 	 */
167 	pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
168 	*pprev = vma_merge(mm, *pprev, start, end, newflags,
169 			vma->anon_vma, vma->vm_file, pgoff, vma_policy(vma));
170 	if (*pprev) {
171 		vma = *pprev;
172 		goto success;
173 	}
174 
175 	*pprev = vma;
176 
177 	if (start != vma->vm_start) {
178 		error = split_vma(mm, vma, start, 1);
179 		if (error)
180 			goto fail;
181 	}
182 
183 	if (end != vma->vm_end) {
184 		error = split_vma(mm, vma, end, 0);
185 		if (error)
186 			goto fail;
187 	}
188 
189 success:
190 	/*
191 	 * vm_flags and vm_page_prot are protected by the mmap_sem
192 	 * held in write mode.
193 	 */
194 	vma->vm_flags = newflags;
195 	vma->vm_page_prot = vm_get_page_prot(newflags);
196 	if (vma_wants_writenotify(vma)) {
197 		vma->vm_page_prot = vm_get_page_prot(newflags & ~VM_SHARED);
198 		dirty_accountable = 1;
199 	}
200 
201 	if (is_vm_hugetlb_page(vma))
202 		hugetlb_change_protection(vma, start, end, vma->vm_page_prot);
203 	else
204 		change_protection(vma, start, end, vma->vm_page_prot, dirty_accountable);
205 	vm_stat_account(mm, oldflags, vma->vm_file, -nrpages);
206 	vm_stat_account(mm, newflags, vma->vm_file, nrpages);
207 	return 0;
208 
209 fail:
210 	vm_unacct_memory(charged);
211 	return error;
212 }
213 
214 asmlinkage long
215 sys_mprotect(unsigned long start, size_t len, unsigned long prot)
216 {
217 	unsigned long vm_flags, nstart, end, tmp, reqprot;
218 	struct vm_area_struct *vma, *prev;
219 	int error = -EINVAL;
220 	const int grows = prot & (PROT_GROWSDOWN|PROT_GROWSUP);
221 	prot &= ~(PROT_GROWSDOWN|PROT_GROWSUP);
222 	if (grows == (PROT_GROWSDOWN|PROT_GROWSUP)) /* can't be both */
223 		return -EINVAL;
224 
225 	if (start & ~PAGE_MASK)
226 		return -EINVAL;
227 	if (!len)
228 		return 0;
229 	len = PAGE_ALIGN(len);
230 	end = start + len;
231 	if (end <= start)
232 		return -ENOMEM;
233 	if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM))
234 		return -EINVAL;
235 
236 	reqprot = prot;
237 	/*
238 	 * Does the application expect PROT_READ to imply PROT_EXEC:
239 	 */
240 	if ((prot & PROT_READ) && (current->personality & READ_IMPLIES_EXEC))
241 		prot |= PROT_EXEC;
242 
243 	vm_flags = calc_vm_prot_bits(prot);
244 
245 	down_write(&current->mm->mmap_sem);
246 
247 	vma = find_vma_prev(current->mm, start, &prev);
248 	error = -ENOMEM;
249 	if (!vma)
250 		goto out;
251 	if (unlikely(grows & PROT_GROWSDOWN)) {
252 		if (vma->vm_start >= end)
253 			goto out;
254 		start = vma->vm_start;
255 		error = -EINVAL;
256 		if (!(vma->vm_flags & VM_GROWSDOWN))
257 			goto out;
258 	}
259 	else {
260 		if (vma->vm_start > start)
261 			goto out;
262 		if (unlikely(grows & PROT_GROWSUP)) {
263 			end = vma->vm_end;
264 			error = -EINVAL;
265 			if (!(vma->vm_flags & VM_GROWSUP))
266 				goto out;
267 		}
268 	}
269 	if (start > vma->vm_start)
270 		prev = vma;
271 
272 	for (nstart = start ; ; ) {
273 		unsigned long newflags;
274 
275 		/* Here we know that  vma->vm_start <= nstart < vma->vm_end. */
276 
277 		newflags = vm_flags | (vma->vm_flags & ~(VM_READ | VM_WRITE | VM_EXEC));
278 
279 		/* newflags >> 4 shift VM_MAY% in place of VM_% */
280 		if ((newflags & ~(newflags >> 4)) & (VM_READ | VM_WRITE | VM_EXEC)) {
281 			error = -EACCES;
282 			goto out;
283 		}
284 
285 		error = security_file_mprotect(vma, reqprot, prot);
286 		if (error)
287 			goto out;
288 
289 		tmp = vma->vm_end;
290 		if (tmp > end)
291 			tmp = end;
292 		error = mprotect_fixup(vma, &prev, nstart, tmp, newflags);
293 		if (error)
294 			goto out;
295 		nstart = tmp;
296 
297 		if (nstart < prev->vm_end)
298 			nstart = prev->vm_end;
299 		if (nstart >= end)
300 			goto out;
301 
302 		vma = prev->vm_next;
303 		if (!vma || vma->vm_start != nstart) {
304 			error = -ENOMEM;
305 			goto out;
306 		}
307 	}
308 out:
309 	up_write(&current->mm->mmap_sem);
310 	return error;
311 }
312