1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /* file-nommu.c: no-MMU version of ramfs
3  *
4  * Copyright (C) 2005 Red Hat, Inc. All Rights Reserved.
5  * Written by David Howells (dhowells@redhat.com)
6  */
7 
8 #include <linux/module.h>
9 #include <linux/fs.h>
10 #include <linux/mm.h>
11 #include <linux/pagemap.h>
12 #include <linux/highmem.h>
13 #include <linux/init.h>
14 #include <linux/string.h>
15 #include <linux/backing-dev.h>
16 #include <linux/ramfs.h>
17 #include <linux/pagevec.h>
18 #include <linux/mman.h>
19 #include <linux/sched.h>
20 #include <linux/slab.h>
21 
22 #include <linux/uaccess.h>
23 #include "internal.h"
24 
25 static int ramfs_nommu_setattr(struct user_namespace *, struct dentry *, struct iattr *);
26 static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
27 						   unsigned long addr,
28 						   unsigned long len,
29 						   unsigned long pgoff,
30 						   unsigned long flags);
31 static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma);
32 
ramfs_mmap_capabilities(struct file * file)33 static unsigned ramfs_mmap_capabilities(struct file *file)
34 {
35 	return NOMMU_MAP_DIRECT | NOMMU_MAP_COPY | NOMMU_MAP_READ |
36 		NOMMU_MAP_WRITE | NOMMU_MAP_EXEC;
37 }
38 
39 const struct file_operations ramfs_file_operations = {
40 	.mmap_capabilities	= ramfs_mmap_capabilities,
41 	.mmap			= ramfs_nommu_mmap,
42 	.get_unmapped_area	= ramfs_nommu_get_unmapped_area,
43 	.read_iter		= generic_file_read_iter,
44 	.write_iter		= generic_file_write_iter,
45 	.fsync			= noop_fsync,
46 	.splice_read		= generic_file_splice_read,
47 	.splice_write		= iter_file_splice_write,
48 	.llseek			= generic_file_llseek,
49 };
50 
51 const struct inode_operations ramfs_file_inode_operations = {
52 	.setattr		= ramfs_nommu_setattr,
53 	.getattr		= simple_getattr,
54 };
55 
56 /*****************************************************************************/
57 /*
58  * add a contiguous set of pages into a ramfs inode when it's truncated from
59  * size 0 on the assumption that it's going to be used for an mmap of shared
60  * memory
61  */
ramfs_nommu_expand_for_mapping(struct inode * inode,size_t newsize)62 int ramfs_nommu_expand_for_mapping(struct inode *inode, size_t newsize)
63 {
64 	unsigned long npages, xpages, loop;
65 	struct page *pages;
66 	unsigned order;
67 	void *data;
68 	int ret;
69 	gfp_t gfp = mapping_gfp_mask(inode->i_mapping);
70 
71 	/* make various checks */
72 	order = get_order(newsize);
73 	if (unlikely(order >= MAX_ORDER))
74 		return -EFBIG;
75 
76 	ret = inode_newsize_ok(inode, newsize);
77 	if (ret)
78 		return ret;
79 
80 	i_size_write(inode, newsize);
81 
82 	/* allocate enough contiguous pages to be able to satisfy the
83 	 * request */
84 	pages = alloc_pages(gfp, order);
85 	if (!pages)
86 		return -ENOMEM;
87 
88 	/* split the high-order page into an array of single pages */
89 	xpages = 1UL << order;
90 	npages = (newsize + PAGE_SIZE - 1) >> PAGE_SHIFT;
91 
92 	split_page(pages, order);
93 
94 	/* trim off any pages we don't actually require */
95 	for (loop = npages; loop < xpages; loop++)
96 		__free_page(pages + loop);
97 
98 	/* clear the memory we allocated */
99 	newsize = PAGE_SIZE * npages;
100 	data = page_address(pages);
101 	memset(data, 0, newsize);
102 
103 	/* attach all the pages to the inode's address space */
104 	for (loop = 0; loop < npages; loop++) {
105 		struct page *page = pages + loop;
106 
107 		ret = add_to_page_cache_lru(page, inode->i_mapping, loop,
108 					gfp);
109 		if (ret < 0)
110 			goto add_error;
111 
112 		/* prevent the page from being discarded on memory pressure */
113 		SetPageDirty(page);
114 		SetPageUptodate(page);
115 
116 		unlock_page(page);
117 		put_page(page);
118 	}
119 
120 	return 0;
121 
122 add_error:
123 	while (loop < npages)
124 		__free_page(pages + loop++);
125 	return ret;
126 }
127 
128 /*****************************************************************************/
129 /*
130  *
131  */
ramfs_nommu_resize(struct inode * inode,loff_t newsize,loff_t size)132 static int ramfs_nommu_resize(struct inode *inode, loff_t newsize, loff_t size)
133 {
134 	int ret;
135 
136 	/* assume a truncate from zero size is going to be for the purposes of
137 	 * shared mmap */
138 	if (size == 0) {
139 		if (unlikely(newsize >> 32))
140 			return -EFBIG;
141 
142 		return ramfs_nommu_expand_for_mapping(inode, newsize);
143 	}
144 
145 	/* check that a decrease in size doesn't cut off any shared mappings */
146 	if (newsize < size) {
147 		ret = nommu_shrink_inode_mappings(inode, size, newsize);
148 		if (ret < 0)
149 			return ret;
150 	}
151 
152 	truncate_setsize(inode, newsize);
153 	return 0;
154 }
155 
156 /*****************************************************************************/
157 /*
158  * handle a change of attributes
159  * - we're specifically interested in a change of size
160  */
ramfs_nommu_setattr(struct user_namespace * mnt_userns,struct dentry * dentry,struct iattr * ia)161 static int ramfs_nommu_setattr(struct user_namespace *mnt_userns,
162 			       struct dentry *dentry, struct iattr *ia)
163 {
164 	struct inode *inode = d_inode(dentry);
165 	unsigned int old_ia_valid = ia->ia_valid;
166 	int ret = 0;
167 
168 	/* POSIX UID/GID verification for setting inode attributes */
169 	ret = setattr_prepare(&init_user_ns, dentry, ia);
170 	if (ret)
171 		return ret;
172 
173 	/* pick out size-changing events */
174 	if (ia->ia_valid & ATTR_SIZE) {
175 		loff_t size = inode->i_size;
176 
177 		if (ia->ia_size != size) {
178 			ret = ramfs_nommu_resize(inode, ia->ia_size, size);
179 			if (ret < 0 || ia->ia_valid == ATTR_SIZE)
180 				goto out;
181 		} else {
182 			/* we skipped the truncate but must still update
183 			 * timestamps
184 			 */
185 			ia->ia_valid |= ATTR_MTIME|ATTR_CTIME;
186 		}
187 	}
188 
189 	setattr_copy(&init_user_ns, inode, ia);
190  out:
191 	ia->ia_valid = old_ia_valid;
192 	return ret;
193 }
194 
195 /*****************************************************************************/
196 /*
197  * try to determine where a shared mapping can be made
198  * - we require that:
199  *   - the pages to be mapped must exist
200  *   - the pages be physically contiguous in sequence
201  */
ramfs_nommu_get_unmapped_area(struct file * file,unsigned long addr,unsigned long len,unsigned long pgoff,unsigned long flags)202 static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
203 					    unsigned long addr, unsigned long len,
204 					    unsigned long pgoff, unsigned long flags)
205 {
206 	unsigned long maxpages, lpages, nr, loop, ret;
207 	struct inode *inode = file_inode(file);
208 	struct page **pages = NULL, **ptr, *page;
209 	loff_t isize;
210 
211 	/* the mapping mustn't extend beyond the EOF */
212 	lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
213 	isize = i_size_read(inode);
214 
215 	ret = -ENOSYS;
216 	maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
217 	if (pgoff >= maxpages)
218 		goto out;
219 
220 	if (maxpages - pgoff < lpages)
221 		goto out;
222 
223 	/* gang-find the pages */
224 	pages = kcalloc(lpages, sizeof(struct page *), GFP_KERNEL);
225 	if (!pages)
226 		goto out_free;
227 
228 	nr = find_get_pages_contig(inode->i_mapping, pgoff, lpages, pages);
229 	if (nr != lpages)
230 		goto out_free_pages; /* leave if some pages were missing */
231 
232 	/* check the pages for physical adjacency */
233 	ptr = pages;
234 	page = *ptr++;
235 	page++;
236 	for (loop = lpages; loop > 1; loop--)
237 		if (*ptr++ != page++)
238 			goto out_free_pages;
239 
240 	/* okay - all conditions fulfilled */
241 	ret = (unsigned long) page_address(pages[0]);
242 
243 out_free_pages:
244 	ptr = pages;
245 	for (loop = nr; loop > 0; loop--)
246 		put_page(*ptr++);
247 out_free:
248 	kfree(pages);
249 out:
250 	return ret;
251 }
252 
253 /*****************************************************************************/
254 /*
255  * set up a mapping for shared memory segments
256  */
ramfs_nommu_mmap(struct file * file,struct vm_area_struct * vma)257 static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma)
258 {
259 	if (!(vma->vm_flags & (VM_SHARED | VM_MAYSHARE)))
260 		return -ENOSYS;
261 
262 	file_accessed(file);
263 	vma->vm_ops = &generic_file_vm_ops;
264 	return 0;
265 }
266