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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 intent is the ext4_mpage_readpages() function here is intended
11 * to replace mpage_readpages() 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#include <linux/cleancache.h>
47
48#include "ext4.h"
49
50#define NUM_PREALLOC_POST_READ_CTXS 128
51
52static struct kmem_cache *bio_post_read_ctx_cache;
53static mempool_t *bio_post_read_ctx_pool;
54
55/* postprocessing steps for read bios */
56enum bio_post_read_step {
57 STEP_INITIAL = 0,
58 STEP_DECRYPT,
59 STEP_VERITY,
60};
61
62struct 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
69static void __read_end_io(struct bio *bio)
70{
71 struct page *page;
72 struct bio_vec *bv;
73 struct bvec_iter_all iter_all;
74
75 bio_for_each_segment_all(bv, bio, iter_all) {
76 page = bv->bv_page;
77
78 /* PG_error was set if any post_read step failed */
79 if (bio->bi_status || PageError(page)) {
80 ClearPageUptodate(page);
81 /* will re-read again later */
82 ClearPageError(page);
83 } else {
84 SetPageUptodate(page);
85 }
86 unlock_page(page);
87 }
88 if (bio->bi_private)
89 mempool_free(bio->bi_private, bio_post_read_ctx_pool);
90 bio_put(bio);
91}
92
93static void bio_post_read_processing(struct bio_post_read_ctx *ctx);
94
95static void decrypt_work(struct work_struct *work)
96{
97 struct bio_post_read_ctx *ctx =
98 container_of(work, struct bio_post_read_ctx, work);
99
100 fscrypt_decrypt_bio(ctx->bio);
101
102 bio_post_read_processing(ctx);
103}
104
105static void verity_work(struct work_struct *work)
106{
107 struct bio_post_read_ctx *ctx =
108 container_of(work, struct bio_post_read_ctx, work);
109
110 fsverity_verify_bio(ctx->bio);
111
112 bio_post_read_processing(ctx);
113}
114
115static void bio_post_read_processing(struct bio_post_read_ctx *ctx)
116{
117 /*
118 * We use different work queues for decryption and for verity because
119 * verity may require reading metadata pages that need decryption, and
120 * we shouldn't recurse to the same workqueue.
121 */
122 switch (++ctx->cur_step) {
123 case STEP_DECRYPT:
124 if (ctx->enabled_steps & (1 << STEP_DECRYPT)) {
125 INIT_WORK(&ctx->work, decrypt_work);
126 fscrypt_enqueue_decrypt_work(&ctx->work);
127 return;
128 }
129 ctx->cur_step++;
130 /* fall-through */
131 case STEP_VERITY:
132 if (ctx->enabled_steps & (1 << STEP_VERITY)) {
133 INIT_WORK(&ctx->work, verity_work);
134 fsverity_enqueue_verify_work(&ctx->work);
135 return;
136 }
137 ctx->cur_step++;
138 /* fall-through */
139 default:
140 __read_end_io(ctx->bio);
141 }
142}
143
144static bool bio_post_read_required(struct bio *bio)
145{
146 return bio->bi_private && !bio->bi_status;
147}
148
149/*
150 * I/O completion handler for multipage BIOs.
151 *
152 * The mpage code never puts partial pages into a BIO (except for end-of-file).
153 * If a page does not map to a contiguous run of blocks then it simply falls
154 * back to block_read_full_page().
155 *
156 * Why is this? If a page's completion depends on a number of different BIOs
157 * which can complete in any order (or at the same time) then determining the
158 * status of that page is hard. See end_buffer_async_read() for the details.
159 * There is no point in duplicating all that complexity.
160 */
161static void mpage_end_io(struct bio *bio)
162{
163 if (bio_post_read_required(bio)) {
164 struct bio_post_read_ctx *ctx = bio->bi_private;
165
166 ctx->cur_step = STEP_INITIAL;
167 bio_post_read_processing(ctx);
168 return;
169 }
170 __read_end_io(bio);
171}
172
173static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx)
174{
175 return fsverity_active(inode) &&
176 idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
177}
178
179static struct bio_post_read_ctx *get_bio_post_read_ctx(struct inode *inode,
180 struct bio *bio,
181 pgoff_t first_idx)
182{
183 unsigned int post_read_steps = 0;
184 struct bio_post_read_ctx *ctx = NULL;
185
186 if (IS_ENCRYPTED(inode) && S_ISREG(inode->i_mode))
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 ctx = mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS);
194 if (!ctx)
195 return ERR_PTR(-ENOMEM);
196 ctx->bio = bio;
197 ctx->enabled_steps = post_read_steps;
198 bio->bi_private = ctx;
199 }
200 return ctx;
201}
202
203static inline loff_t ext4_readpage_limit(struct inode *inode)
204{
205 if (IS_ENABLED(CONFIG_FS_VERITY) &&
206 (IS_VERITY(inode) || ext4_verity_in_progress(inode)))
207 return inode->i_sb->s_maxbytes;
208
209 return i_size_read(inode);
210}
211
212int ext4_mpage_readpages(struct address_space *mapping,
213 struct list_head *pages, struct page *page,
214 unsigned nr_pages, bool is_readahead)
215{
216 struct bio *bio = NULL;
217 sector_t last_block_in_bio = 0;
218
219 struct inode *inode = mapping->host;
220 const unsigned blkbits = inode->i_blkbits;
221 const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
222 const unsigned blocksize = 1 << blkbits;
223 sector_t block_in_file;
224 sector_t last_block;
225 sector_t last_block_in_file;
226 sector_t blocks[MAX_BUF_PER_PAGE];
227 unsigned page_block;
228 struct block_device *bdev = inode->i_sb->s_bdev;
229 int length;
230 unsigned relative_block = 0;
231 struct ext4_map_blocks map;
232
233 map.m_pblk = 0;
234 map.m_lblk = 0;
235 map.m_len = 0;
236 map.m_flags = 0;
237
238 for (; nr_pages; nr_pages--) {
239 int fully_mapped = 1;
240 unsigned first_hole = blocks_per_page;
241
242 if (pages) {
243 page = lru_to_page(pages);
244
245 prefetchw(&page->flags);
246 list_del(&page->lru);
247 if (add_to_page_cache_lru(page, mapping, page->index,
248 readahead_gfp_mask(mapping)))
249 goto next_page;
250 }
251
252 if (page_has_buffers(page))
253 goto confused;
254
255 block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
256 last_block = block_in_file + nr_pages * blocks_per_page;
257 last_block_in_file = (ext4_readpage_limit(inode) +
258 blocksize - 1) >> blkbits;
259 if (last_block > last_block_in_file)
260 last_block = last_block_in_file;
261 page_block = 0;
262
263 /*
264 * Map blocks using the previous result first.
265 */
266 if ((map.m_flags & EXT4_MAP_MAPPED) &&
267 block_in_file > map.m_lblk &&
268 block_in_file < (map.m_lblk + map.m_len)) {
269 unsigned map_offset = block_in_file - map.m_lblk;
270 unsigned last = map.m_len - map_offset;
271
272 for (relative_block = 0; ; relative_block++) {
273 if (relative_block == last) {
274 /* needed? */
275 map.m_flags &= ~EXT4_MAP_MAPPED;
276 break;
277 }
278 if (page_block == blocks_per_page)
279 break;
280 blocks[page_block] = map.m_pblk + map_offset +
281 relative_block;
282 page_block++;
283 block_in_file++;
284 }
285 }
286
287 /*
288 * Then do more ext4_map_blocks() calls until we are
289 * done with this page.
290 */
291 while (page_block < blocks_per_page) {
292 if (block_in_file < last_block) {
293 map.m_lblk = block_in_file;
294 map.m_len = last_block - block_in_file;
295
296 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
297 set_error_page:
298 SetPageError(page);
299 zero_user_segment(page, 0,
300 PAGE_SIZE);
301 unlock_page(page);
302 goto next_page;
303 }
304 }
305 if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
306 fully_mapped = 0;
307 if (first_hole == blocks_per_page)
308 first_hole = page_block;
309 page_block++;
310 block_in_file++;
311 continue;
312 }
313 if (first_hole != blocks_per_page)
314 goto confused; /* hole -> non-hole */
315
316 /* Contiguous blocks? */
317 if (page_block && blocks[page_block-1] != map.m_pblk-1)
318 goto confused;
319 for (relative_block = 0; ; relative_block++) {
320 if (relative_block == map.m_len) {
321 /* needed? */
322 map.m_flags &= ~EXT4_MAP_MAPPED;
323 break;
324 } else if (page_block == blocks_per_page)
325 break;
326 blocks[page_block] = map.m_pblk+relative_block;
327 page_block++;
328 block_in_file++;
329 }
330 }
331 if (first_hole != blocks_per_page) {
332 zero_user_segment(page, first_hole << blkbits,
333 PAGE_SIZE);
334 if (first_hole == 0) {
335 if (ext4_need_verity(inode, page->index) &&
336 !fsverity_verify_page(page))
337 goto set_error_page;
338 SetPageUptodate(page);
339 unlock_page(page);
340 goto next_page;
341 }
342 } else if (fully_mapped) {
343 SetPageMappedToDisk(page);
344 }
345 if (fully_mapped && blocks_per_page == 1 &&
346 !PageUptodate(page) && cleancache_get_page(page) == 0) {
347 SetPageUptodate(page);
348 goto confused;
349 }
350
351 /*
352 * This page will go to BIO. Do we need to send this
353 * BIO off first?
354 */
355 if (bio && (last_block_in_bio != blocks[0] - 1)) {
356 submit_and_realloc:
357 submit_bio(bio);
358 bio = NULL;
359 }
360 if (bio == NULL) {
361 struct bio_post_read_ctx *ctx;
362
363 bio = bio_alloc(GFP_KERNEL,
364 min_t(int, nr_pages, BIO_MAX_PAGES));
365 if (!bio)
366 goto set_error_page;
367 ctx = get_bio_post_read_ctx(inode, bio, page->index);
368 if (IS_ERR(ctx)) {
369 bio_put(bio);
370 bio = NULL;
371 goto set_error_page;
372 }
373 bio_set_dev(bio, bdev);
374 bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
375 bio->bi_end_io = mpage_end_io;
376 bio->bi_private = ctx;
377 bio_set_op_attrs(bio, REQ_OP_READ,
378 is_readahead ? REQ_RAHEAD : 0);
379 }
380
381 length = first_hole << blkbits;
382 if (bio_add_page(bio, page, length, 0) < length)
383 goto submit_and_realloc;
384
385 if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
386 (relative_block == map.m_len)) ||
387 (first_hole != blocks_per_page)) {
388 submit_bio(bio);
389 bio = NULL;
390 } else
391 last_block_in_bio = blocks[blocks_per_page - 1];
392 goto next_page;
393 confused:
394 if (bio) {
395 submit_bio(bio);
396 bio = NULL;
397 }
398 if (!PageUptodate(page))
399 block_read_full_page(page, ext4_get_block);
400 else
401 unlock_page(page);
402 next_page:
403 if (pages)
404 put_page(page);
405 }
406 BUG_ON(pages && !list_empty(pages));
407 if (bio)
408 submit_bio(bio);
409 return 0;
410}
411
412int __init ext4_init_post_read_processing(void)
413{
414 bio_post_read_ctx_cache =
415 kmem_cache_create("ext4_bio_post_read_ctx",
416 sizeof(struct bio_post_read_ctx), 0, 0, NULL);
417 if (!bio_post_read_ctx_cache)
418 goto fail;
419 bio_post_read_ctx_pool =
420 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,
421 bio_post_read_ctx_cache);
422 if (!bio_post_read_ctx_pool)
423 goto fail_free_cache;
424 return 0;
425
426fail_free_cache:
427 kmem_cache_destroy(bio_post_read_ctx_cache);
428fail:
429 return -ENOMEM;
430}
431
432void ext4_exit_post_read_processing(void)
433{
434 mempool_destroy(bio_post_read_ctx_pool);
435 kmem_cache_destroy(bio_post_read_ctx_cache);
436}