Line data Source code
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 0 : static void __read_end_io(struct bio *bio)
70 : {
71 0 : struct folio_iter fi;
72 :
73 0 : bio_for_each_folio_all(fi, bio) {
74 0 : struct folio *folio = fi.folio;
75 :
76 0 : if (bio->bi_status)
77 0 : folio_clear_uptodate(folio);
78 : else
79 0 : folio_mark_uptodate(folio);
80 0 : folio_unlock(folio);
81 : }
82 0 : if (bio->bi_private)
83 0 : mempool_free(bio->bi_private, bio_post_read_ctx_pool);
84 0 : bio_put(bio);
85 0 : }
86 :
87 : static void bio_post_read_processing(struct bio_post_read_ctx *ctx);
88 :
89 0 : static void decrypt_work(struct work_struct *work)
90 : {
91 0 : struct bio_post_read_ctx *ctx =
92 0 : container_of(work, struct bio_post_read_ctx, work);
93 0 : struct bio *bio = ctx->bio;
94 :
95 0 : if (fscrypt_decrypt_bio(bio))
96 0 : bio_post_read_processing(ctx);
97 : else
98 : __read_end_io(bio);
99 0 : }
100 :
101 0 : static void verity_work(struct work_struct *work)
102 : {
103 0 : struct bio_post_read_ctx *ctx =
104 0 : container_of(work, struct bio_post_read_ctx, work);
105 0 : struct bio *bio = ctx->bio;
106 :
107 : /*
108 : * fsverity_verify_bio() may call readahead() again, and although verity
109 : * will be disabled for that, decryption may still be needed, causing
110 : * another bio_post_read_ctx to be allocated. So to guarantee that
111 : * mempool_alloc() never deadlocks we must free the current ctx first.
112 : * This is safe because verity is the last post-read step.
113 : */
114 0 : BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX);
115 0 : mempool_free(ctx, bio_post_read_ctx_pool);
116 0 : bio->bi_private = NULL;
117 :
118 0 : fsverity_verify_bio(bio);
119 :
120 0 : __read_end_io(bio);
121 0 : }
122 :
123 0 : static void bio_post_read_processing(struct bio_post_read_ctx *ctx)
124 : {
125 : /*
126 : * We use different work queues for decryption and for verity because
127 : * verity may require reading metadata pages that need decryption, and
128 : * we shouldn't recurse to the same workqueue.
129 : */
130 0 : switch (++ctx->cur_step) {
131 0 : case STEP_DECRYPT:
132 0 : if (ctx->enabled_steps & (1 << STEP_DECRYPT)) {
133 0 : INIT_WORK(&ctx->work, decrypt_work);
134 0 : fscrypt_enqueue_decrypt_work(&ctx->work);
135 0 : return;
136 : }
137 0 : ctx->cur_step++;
138 0 : fallthrough;
139 0 : case STEP_VERITY:
140 0 : if (ctx->enabled_steps & (1 << STEP_VERITY)) {
141 0 : INIT_WORK(&ctx->work, verity_work);
142 0 : fsverity_enqueue_verify_work(&ctx->work);
143 0 : return;
144 : }
145 0 : ctx->cur_step++;
146 0 : fallthrough;
147 0 : default:
148 0 : __read_end_io(ctx->bio);
149 : }
150 : }
151 :
152 : static bool bio_post_read_required(struct bio *bio)
153 : {
154 0 : return bio->bi_private && !bio->bi_status;
155 : }
156 :
157 : /*
158 : * I/O completion handler for multipage BIOs.
159 : *
160 : * The mpage code never puts partial pages into a BIO (except for end-of-file).
161 : * If a page does not map to a contiguous run of blocks then it simply falls
162 : * back to block_read_full_folio().
163 : *
164 : * Why is this? If a page's completion depends on a number of different BIOs
165 : * which can complete in any order (or at the same time) then determining the
166 : * status of that page is hard. See end_buffer_async_read() for the details.
167 : * There is no point in duplicating all that complexity.
168 : */
169 0 : static void mpage_end_io(struct bio *bio)
170 : {
171 0 : if (bio_post_read_required(bio)) {
172 0 : struct bio_post_read_ctx *ctx = bio->bi_private;
173 :
174 0 : ctx->cur_step = STEP_INITIAL;
175 0 : bio_post_read_processing(ctx);
176 0 : return;
177 : }
178 0 : __read_end_io(bio);
179 : }
180 :
181 : static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx)
182 : {
183 : return fsverity_active(inode) &&
184 : idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
185 : }
186 :
187 : static void ext4_set_bio_post_read_ctx(struct bio *bio,
188 : const struct inode *inode,
189 : pgoff_t first_idx)
190 : {
191 : unsigned int post_read_steps = 0;
192 :
193 : if (fscrypt_inode_uses_fs_layer_crypto(inode))
194 : post_read_steps |= 1 << STEP_DECRYPT;
195 :
196 : if (ext4_need_verity(inode, first_idx))
197 : post_read_steps |= 1 << STEP_VERITY;
198 :
199 : if (post_read_steps) {
200 : /* Due to the mempool, this never fails. */
201 : struct bio_post_read_ctx *ctx =
202 : mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS);
203 :
204 : ctx->bio = bio;
205 : ctx->enabled_steps = post_read_steps;
206 : bio->bi_private = ctx;
207 : }
208 : }
209 :
210 : static inline loff_t ext4_readpage_limit(struct inode *inode)
211 : {
212 0 : if (IS_ENABLED(CONFIG_FS_VERITY) && IS_VERITY(inode))
213 : return inode->i_sb->s_maxbytes;
214 :
215 0 : return i_size_read(inode);
216 : }
217 :
218 0 : int ext4_mpage_readpages(struct inode *inode,
219 : struct readahead_control *rac, struct folio *folio)
220 : {
221 0 : struct bio *bio = NULL;
222 0 : sector_t last_block_in_bio = 0;
223 :
224 0 : const unsigned blkbits = inode->i_blkbits;
225 0 : const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
226 0 : const unsigned blocksize = 1 << blkbits;
227 0 : sector_t next_block;
228 0 : sector_t block_in_file;
229 0 : sector_t last_block;
230 0 : sector_t last_block_in_file;
231 0 : sector_t blocks[MAX_BUF_PER_PAGE];
232 0 : unsigned page_block;
233 0 : struct block_device *bdev = inode->i_sb->s_bdev;
234 0 : int length;
235 0 : unsigned relative_block = 0;
236 0 : struct ext4_map_blocks map;
237 0 : unsigned int nr_pages = rac ? readahead_count(rac) : 1;
238 :
239 0 : map.m_pblk = 0;
240 0 : map.m_lblk = 0;
241 0 : map.m_len = 0;
242 0 : map.m_flags = 0;
243 :
244 0 : for (; nr_pages; nr_pages--) {
245 0 : int fully_mapped = 1;
246 0 : unsigned first_hole = blocks_per_page;
247 :
248 0 : if (rac)
249 0 : folio = readahead_folio(rac);
250 0 : prefetchw(&folio->flags);
251 :
252 0 : if (folio_buffers(folio))
253 0 : goto confused;
254 :
255 0 : block_in_file = next_block =
256 0 : (sector_t)folio->index << (PAGE_SHIFT - blkbits);
257 0 : last_block = block_in_file + nr_pages * blocks_per_page;
258 0 : last_block_in_file = (ext4_readpage_limit(inode) +
259 0 : blocksize - 1) >> blkbits;
260 0 : if (last_block > last_block_in_file)
261 : last_block = last_block_in_file;
262 0 : page_block = 0;
263 :
264 : /*
265 : * Map blocks using the previous result first.
266 : */
267 0 : if ((map.m_flags & EXT4_MAP_MAPPED) &&
268 0 : block_in_file > map.m_lblk &&
269 0 : block_in_file < (map.m_lblk + map.m_len)) {
270 0 : unsigned map_offset = block_in_file - map.m_lblk;
271 0 : unsigned last = map.m_len - map_offset;
272 :
273 0 : for (relative_block = 0; ; relative_block++) {
274 0 : if (relative_block == last) {
275 : /* needed? */
276 0 : map.m_flags &= ~EXT4_MAP_MAPPED;
277 0 : break;
278 : }
279 0 : if (page_block == blocks_per_page)
280 : break;
281 0 : blocks[page_block] = map.m_pblk + map_offset +
282 : relative_block;
283 0 : page_block++;
284 0 : block_in_file++;
285 : }
286 : }
287 :
288 : /*
289 : * Then do more ext4_map_blocks() calls until we are
290 : * done with this folio.
291 : */
292 0 : while (page_block < blocks_per_page) {
293 0 : if (block_in_file < last_block) {
294 0 : map.m_lblk = block_in_file;
295 0 : map.m_len = last_block - block_in_file;
296 :
297 0 : if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
298 0 : set_error_page:
299 0 : folio_set_error(folio);
300 0 : folio_zero_segment(folio, 0,
301 : folio_size(folio));
302 0 : folio_unlock(folio);
303 0 : goto next_page;
304 : }
305 : }
306 0 : if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
307 0 : fully_mapped = 0;
308 0 : if (first_hole == blocks_per_page)
309 0 : first_hole = page_block;
310 0 : page_block++;
311 0 : block_in_file++;
312 0 : continue;
313 : }
314 0 : if (first_hole != blocks_per_page)
315 0 : goto confused; /* hole -> non-hole */
316 :
317 : /* Contiguous blocks? */
318 0 : if (page_block && blocks[page_block-1] != map.m_pblk-1)
319 0 : goto confused;
320 0 : for (relative_block = 0; ; relative_block++) {
321 0 : if (relative_block == map.m_len) {
322 : /* needed? */
323 0 : map.m_flags &= ~EXT4_MAP_MAPPED;
324 0 : break;
325 0 : } else if (page_block == blocks_per_page)
326 : break;
327 0 : blocks[page_block] = map.m_pblk+relative_block;
328 0 : page_block++;
329 0 : block_in_file++;
330 : }
331 : }
332 0 : if (first_hole != blocks_per_page) {
333 0 : folio_zero_segment(folio, first_hole << blkbits,
334 : folio_size(folio));
335 0 : if (first_hole == 0) {
336 0 : if (ext4_need_verity(inode, folio->index) &&
337 : !fsverity_verify_folio(folio))
338 : goto set_error_page;
339 0 : folio_mark_uptodate(folio);
340 0 : folio_unlock(folio);
341 0 : continue;
342 : }
343 0 : } else if (fully_mapped) {
344 0 : folio_set_mappedtodisk(folio);
345 : }
346 :
347 : /*
348 : * This folio will go to BIO. Do we need to send this
349 : * BIO off first?
350 : */
351 0 : if (bio && (last_block_in_bio != blocks[0] - 1 ||
352 : !fscrypt_mergeable_bio(bio, inode, next_block))) {
353 0 : submit_and_realloc:
354 0 : submit_bio(bio);
355 0 : bio = NULL;
356 : }
357 0 : if (bio == NULL) {
358 : /*
359 : * bio_alloc will _always_ be able to allocate a bio if
360 : * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
361 : */
362 0 : bio = bio_alloc(bdev, bio_max_segs(nr_pages),
363 : REQ_OP_READ, GFP_KERNEL);
364 0 : fscrypt_set_bio_crypt_ctx(bio, inode, next_block,
365 : GFP_KERNEL);
366 0 : ext4_set_bio_post_read_ctx(bio, inode, folio->index);
367 0 : bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
368 0 : bio->bi_end_io = mpage_end_io;
369 0 : if (rac)
370 0 : bio->bi_opf |= REQ_RAHEAD;
371 : }
372 :
373 0 : length = first_hole << blkbits;
374 0 : if (!bio_add_folio(bio, folio, length, 0))
375 0 : goto submit_and_realloc;
376 :
377 0 : if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
378 0 : (relative_block == map.m_len)) ||
379 : (first_hole != blocks_per_page)) {
380 0 : submit_bio(bio);
381 0 : bio = NULL;
382 : } else
383 0 : last_block_in_bio = blocks[blocks_per_page - 1];
384 0 : continue;
385 0 : confused:
386 0 : if (bio) {
387 0 : submit_bio(bio);
388 0 : bio = NULL;
389 : }
390 0 : if (!folio_test_uptodate(folio))
391 0 : block_read_full_folio(folio, ext4_get_block);
392 : else
393 0 : folio_unlock(folio);
394 0 : next_page:
395 0 : ; /* A label shall be followed by a statement until C23 */
396 : }
397 0 : if (bio)
398 0 : submit_bio(bio);
399 0 : return 0;
400 : }
401 :
402 2 : int __init ext4_init_post_read_processing(void)
403 : {
404 2 : bio_post_read_ctx_cache = KMEM_CACHE(bio_post_read_ctx, SLAB_RECLAIM_ACCOUNT);
405 :
406 2 : if (!bio_post_read_ctx_cache)
407 0 : goto fail;
408 2 : bio_post_read_ctx_pool =
409 : mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,
410 : bio_post_read_ctx_cache);
411 2 : if (!bio_post_read_ctx_pool)
412 0 : goto fail_free_cache;
413 : return 0;
414 :
415 : fail_free_cache:
416 0 : kmem_cache_destroy(bio_post_read_ctx_cache);
417 : fail:
418 : return -ENOMEM;
419 : }
420 :
421 0 : void ext4_exit_post_read_processing(void)
422 : {
423 0 : mempool_destroy(bio_post_read_ctx_pool);
424 0 : kmem_cache_destroy(bio_post_read_ctx_cache);
425 0 : }
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