1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * linux/fs/ext4/readpage.c
4 *
5 * Copyright (C) 2002, Linus Torvalds.
6 * Copyright (C) 2015, Google, Inc.
7 *
8 * This was originally taken from fs/mpage.c
9 *
10 * The ext4_mpage_readpages() function here is intended to
11 * replace mpage_readahead() in the general case, not just for
12 * encrypted files. It has some limitations (see below), where it
13 * will fall back to read_block_full_page(), but these limitations
14 * should only be hit when page_size != block_size.
15 *
16 * This will allow us to attach a callback function to support ext4
17 * encryption.
18 *
19 * If anything unusual happens, such as:
20 *
21 * - encountering a page which has buffers
22 * - encountering a page which has a non-hole after a hole
23 * - encountering a page with non-contiguous blocks
24 *
25 * then this code just gives up and calls the buffer_head-based read function.
26 * It does handle a page which has holes at the end - that is a common case:
27 * the end-of-file on blocksize < PAGE_SIZE setups.
28 *
29 */
30
31 #include <linux/kernel.h>
32 #include <linux/export.h>
33 #include <linux/mm.h>
34 #include <linux/kdev_t.h>
35 #include <linux/gfp.h>
36 #include <linux/bio.h>
37 #include <linux/fs.h>
38 #include <linux/buffer_head.h>
39 #include <linux/blkdev.h>
40 #include <linux/highmem.h>
41 #include <linux/prefetch.h>
42 #include <linux/mpage.h>
43 #include <linux/writeback.h>
44 #include <linux/backing-dev.h>
45 #include <linux/pagevec.h>
46
47 #include "ext4.h"
48
49 #define NUM_PREALLOC_POST_READ_CTXS 128
50
51 static struct kmem_cache *bio_post_read_ctx_cache;
52 static mempool_t *bio_post_read_ctx_pool;
53
54 /* postprocessing steps for read bios */
55 enum bio_post_read_step {
56 STEP_INITIAL = 0,
57 STEP_DECRYPT,
58 STEP_VERITY,
59 STEP_MAX,
60 };
61
62 struct bio_post_read_ctx {
63 struct bio *bio;
64 struct work_struct work;
65 unsigned int cur_step;
66 unsigned int enabled_steps;
67 };
68
69 static void __read_end_io(struct bio *bio)
70 {
71 struct folio_iter fi;
72
73 bio_for_each_folio_all(fi, bio)
74 folio_end_read(fi.folio, bio->bi_status == 0);
75 if (bio->bi_private)
76 mempool_free(bio->bi_private, bio_post_read_ctx_pool);
77 bio_put(bio);
78 }
79
80 static void bio_post_read_processing(struct bio_post_read_ctx *ctx);
81
82 static void decrypt_work(struct work_struct *work)
83 {
84 struct bio_post_read_ctx *ctx =
85 container_of(work, struct bio_post_read_ctx, work);
86 struct bio *bio = ctx->bio;
87
88 if (fscrypt_decrypt_bio(bio))
89 bio_post_read_processing(ctx);
90 else
91 __read_end_io(bio);
92 }
93
94 static void verity_work(struct work_struct *work)
95 {
96 struct bio_post_read_ctx *ctx =
97 container_of(work, struct bio_post_read_ctx, work);
98 struct bio *bio = ctx->bio;
99
100 /*
101 * fsverity_verify_bio() may call readahead() again, and although verity
102 * will be disabled for that, decryption may still be needed, causing
103 * another bio_post_read_ctx to be allocated. So to guarantee that
104 * mempool_alloc() never deadlocks we must free the current ctx first.
105 * This is safe because verity is the last post-read step.
106 */
107 BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX);
108 mempool_free(ctx, bio_post_read_ctx_pool);
109 bio->bi_private = NULL;
110
111 fsverity_verify_bio(bio);
112
113 __read_end_io(bio);
114 }
115
116 static void bio_post_read_processing(struct bio_post_read_ctx *ctx)
117 {
118 /*
119 * We use different work queues for decryption and for verity because
120 * verity may require reading metadata pages that need decryption, and
121 * we shouldn't recurse to the same workqueue.
122 */
123 switch (++ctx->cur_step) {
124 case STEP_DECRYPT:
125 if (ctx->enabled_steps & (1 << STEP_DECRYPT)) {
126 INIT_WORK(&ctx->work, decrypt_work);
127 fscrypt_enqueue_decrypt_work(&ctx->work);
128 return;
129 }
130 ctx->cur_step++;
131 fallthrough;
132 case STEP_VERITY:
133 if (ctx->enabled_steps & (1 << STEP_VERITY)) {
134 INIT_WORK(&ctx->work, verity_work);
135 fsverity_enqueue_verify_work(&ctx->work);
136 return;
137 }
138 ctx->cur_step++;
139 fallthrough;
140 default:
141 __read_end_io(ctx->bio);
142 }
143 }
144
145 static bool bio_post_read_required(struct bio *bio)
146 {
147 return bio->bi_private && !bio->bi_status;
148 }
149
150 /*
151 * I/O completion handler for multipage BIOs.
152 *
153 * The mpage code never puts partial pages into a BIO (except for end-of-file).
154 * If a page does not map to a contiguous run of blocks then it simply falls
155 * back to block_read_full_folio().
156 *
157 * Why is this? If a page's completion depends on a number of different BIOs
158 * which can complete in any order (or at the same time) then determining the
159 * status of that page is hard. See end_buffer_async_read() for the details.
160 * There is no point in duplicating all that complexity.
161 */
162 static void mpage_end_io(struct bio *bio)
163 {
164 if (bio_post_read_required(bio)) {
165 struct bio_post_read_ctx *ctx = bio->bi_private;
166
167 ctx->cur_step = STEP_INITIAL;
168 bio_post_read_processing(ctx);
169 return;
170 }
171 __read_end_io(bio);
172 }
173
174 static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx)
175 {
176 return fsverity_active(inode) &&
177 idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
178 }
179
180 static void ext4_set_bio_post_read_ctx(struct bio *bio,
181 const struct inode *inode,
182 pgoff_t first_idx)
183 {
184 unsigned int post_read_steps = 0;
185
186 if (fscrypt_inode_uses_fs_layer_crypto(inode))
187 post_read_steps |= 1 << STEP_DECRYPT;
188
189 if (ext4_need_verity(inode, first_idx))
190 post_read_steps |= 1 << STEP_VERITY;
191
192 if (post_read_steps) {
193 /* Due to the mempool, this never fails. */
194 struct bio_post_read_ctx *ctx =
195 mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS);
196
197 ctx->bio = bio;
198 ctx->enabled_steps = post_read_steps;
199 bio->bi_private = ctx;
200 }
201 }
202
203 static inline loff_t ext4_readpage_limit(struct inode *inode)
204 {
205 if (IS_ENABLED(CONFIG_FS_VERITY) && IS_VERITY(inode))
206 return inode->i_sb->s_maxbytes;
207
208 return i_size_read(inode);
209 }
210
211 int ext4_mpage_readpages(struct inode *inode,
212 struct readahead_control *rac, struct folio *folio)
213 {
214 struct bio *bio = NULL;
215 sector_t last_block_in_bio = 0;
216
217 const unsigned blkbits = inode->i_blkbits;
218 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
219 const unsigned blocksize = 1 << blkbits;
220 sector_t next_block;
221 sector_t block_in_file;
222 sector_t last_block;
223 sector_t last_block_in_file;
224 sector_t blocks[MAX_BUF_PER_PAGE];
225 unsigned page_block;
226 struct block_device *bdev = inode->i_sb->s_bdev;
227 int length;
228 unsigned relative_block = 0;
229 struct ext4_map_blocks map;
230 unsigned int nr_pages = rac ? readahead_count(rac) : 1;
231
232 map.m_pblk = 0;
233 map.m_lblk = 0;
234 map.m_len = 0;
235 map.m_flags = 0;
236
237 for (; nr_pages; nr_pages--) {
238 int fully_mapped = 1;
239 unsigned first_hole = blocks_per_page;
240
241 if (rac)
242 folio = readahead_folio(rac);
243 prefetchw(&folio->flags);
244
245 if (folio_buffers(folio))
246 goto confused;
247
248 block_in_file = next_block =
249 (sector_t)folio->index << (PAGE_SHIFT - blkbits);
250 last_block = block_in_file + nr_pages * blocks_per_page;
251 last_block_in_file = (ext4_readpage_limit(inode) +
252 blocksize - 1) >> blkbits;
253 if (last_block > last_block_in_file)
254 last_block = last_block_in_file;
255 page_block = 0;
256
257 /*
258 * Map blocks using the previous result first.
259 */
260 if ((map.m_flags & EXT4_MAP_MAPPED) &&
261 block_in_file > map.m_lblk &&
262 block_in_file < (map.m_lblk + map.m_len)) {
263 unsigned map_offset = block_in_file - map.m_lblk;
264 unsigned last = map.m_len - map_offset;
265
266 for (relative_block = 0; ; relative_block++) {
267 if (relative_block == last) {
268 /* needed? */
269 map.m_flags &= ~EXT4_MAP_MAPPED;
270 break;
271 }
272 if (page_block == blocks_per_page)
273 break;
274 blocks[page_block] = map.m_pblk + map_offset +
275 relative_block;
276 page_block++;
277 block_in_file++;
278 }
279 }
280
281 /*
282 * Then do more ext4_map_blocks() calls until we are
283 * done with this folio.
284 */
285 while (page_block < blocks_per_page) {
286 if (block_in_file < last_block) {
287 map.m_lblk = block_in_file;
288 map.m_len = last_block - block_in_file;
289
290 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
291 set_error_page:
292 folio_zero_segment(folio, 0,
293 folio_size(folio));
294 folio_unlock(folio);
295 goto next_page;
296 }
297 }
298 if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
299 fully_mapped = 0;
300 if (first_hole == blocks_per_page)
301 first_hole = page_block;
302 page_block++;
303 block_in_file++;
304 continue;
305 }
306 if (first_hole != blocks_per_page)
307 goto confused; /* hole -> non-hole */
308
309 /* Contiguous blocks? */
310 if (page_block && blocks[page_block-1] != map.m_pblk-1)
311 goto confused;
312 for (relative_block = 0; ; relative_block++) {
313 if (relative_block == map.m_len) {
314 /* needed? */
315 map.m_flags &= ~EXT4_MAP_MAPPED;
316 break;
317 } else if (page_block == blocks_per_page)
318 break;
319 blocks[page_block] = map.m_pblk+relative_block;
320 page_block++;
321 block_in_file++;
322 }
323 }
324 if (first_hole != blocks_per_page) {
325 folio_zero_segment(folio, first_hole << blkbits,
326 folio_size(folio));
327 if (first_hole == 0) {
328 if (ext4_need_verity(inode, folio->index) &&
329 !fsverity_verify_folio(folio))
330 goto set_error_page;
331 folio_end_read(folio, true);
332 continue;
333 }
334 } else if (fully_mapped) {
335 folio_set_mappedtodisk(folio);
336 }
337
338 /*
339 * This folio will go to BIO. Do we need to send this
340 * BIO off first?
341 */
342 if (bio && (last_block_in_bio != blocks[0] - 1 ||
343 !fscrypt_mergeable_bio(bio, inode, next_block))) {
344 submit_and_realloc:
345 submit_bio(bio);
346 bio = NULL;
347 }
348 if (bio == NULL) {
349 /*
350 * bio_alloc will _always_ be able to allocate a bio if
351 * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
352 */
353 bio = bio_alloc(bdev, bio_max_segs(nr_pages),
354 REQ_OP_READ, GFP_KERNEL);
355 fscrypt_set_bio_crypt_ctx(bio, inode, next_block,
356 GFP_KERNEL);
357 ext4_set_bio_post_read_ctx(bio, inode, folio->index);
358 bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
359 bio->bi_end_io = mpage_end_io;
360 if (rac)
361 bio->bi_opf |= REQ_RAHEAD;
362 }
363
364 length = first_hole << blkbits;
365 if (!bio_add_folio(bio, folio, length, 0))
366 goto submit_and_realloc;
367
368 if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
369 (relative_block == map.m_len)) ||
370 (first_hole != blocks_per_page)) {
371 submit_bio(bio);
372 bio = NULL;
373 } else
374 last_block_in_bio = blocks[blocks_per_page - 1];
375 continue;
376 confused:
377 if (bio) {
378 submit_bio(bio);
379 bio = NULL;
380 }
381 if (!folio_test_uptodate(folio))
382 block_read_full_folio(folio, ext4_get_block);
383 else
384 folio_unlock(folio);
385 next_page:
386 ; /* A label shall be followed by a statement until C23 */
387 }
388 if (bio)
389 submit_bio(bio);
390 return 0;
391 }
392
393 int __init ext4_init_post_read_processing(void)
394 {
395 bio_post_read_ctx_cache = KMEM_CACHE(bio_post_read_ctx, SLAB_RECLAIM_ACCOUNT);
396
397 if (!bio_post_read_ctx_cache)
398 goto fail;
399 bio_post_read_ctx_pool =
400 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,
401 bio_post_read_ctx_cache);
402 if (!bio_post_read_ctx_pool)
403 goto fail_free_cache;
404 return 0;
405
406 fail_free_cache:
407 kmem_cache_destroy(bio_post_read_ctx_cache);
408 fail:
409 return -ENOMEM;
410 }
411
412 void ext4_exit_post_read_processing(void)
413 {
414 mempool_destroy(bio_post_read_ctx_pool);
415 kmem_cache_destroy(bio_post_read_ctx_cache);
416 }
417
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