3d21eae267fcaba2126febe294eb157148c226cc
[releases.git] / readpage.c
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 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 verity 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
93 static void bio_post_read_processing(struct bio_post_read_ctx *ctx);
94
95 static 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         struct bio *bio = ctx->bio;
100
101         if (fscrypt_decrypt_bio(bio))
102                 bio_post_read_processing(ctx);
103         else
104                 __read_end_io(bio);
105 }
106
107 static void verity_work(struct work_struct *work)
108 {
109         struct bio_post_read_ctx *ctx =
110                 container_of(work, struct bio_post_read_ctx, work);
111         struct bio *bio = ctx->bio;
112
113         /*
114          * fsverity_verify_bio() may call readahead() again, and although verity
115          * will be disabled for that, decryption may still be needed, causing
116          * another bio_post_read_ctx to be allocated.  So to guarantee that
117          * mempool_alloc() never deadlocks we must free the current ctx first.
118          * This is safe because verity is the last post-read step.
119          */
120         BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX);
121         mempool_free(ctx, bio_post_read_ctx_pool);
122         bio->bi_private = NULL;
123
124         fsverity_verify_bio(bio);
125
126         __read_end_io(bio);
127 }
128
129 static void bio_post_read_processing(struct bio_post_read_ctx *ctx)
130 {
131         /*
132          * We use different work queues for decryption and for verity because
133          * verity may require reading metadata pages that need decryption, and
134          * we shouldn't recurse to the same workqueue.
135          */
136         switch (++ctx->cur_step) {
137         case STEP_DECRYPT:
138                 if (ctx->enabled_steps & (1 << STEP_DECRYPT)) {
139                         INIT_WORK(&ctx->work, decrypt_work);
140                         fscrypt_enqueue_decrypt_work(&ctx->work);
141                         return;
142                 }
143                 ctx->cur_step++;
144                 fallthrough;
145         case STEP_VERITY:
146                 if (ctx->enabled_steps & (1 << STEP_VERITY)) {
147                         INIT_WORK(&ctx->work, verity_work);
148                         fsverity_enqueue_verify_work(&ctx->work);
149                         return;
150                 }
151                 ctx->cur_step++;
152                 fallthrough;
153         default:
154                 __read_end_io(ctx->bio);
155         }
156 }
157
158 static bool bio_post_read_required(struct bio *bio)
159 {
160         return bio->bi_private && !bio->bi_status;
161 }
162
163 /*
164  * I/O completion handler for multipage BIOs.
165  *
166  * The mpage code never puts partial pages into a BIO (except for end-of-file).
167  * If a page does not map to a contiguous run of blocks then it simply falls
168  * back to block_read_full_folio().
169  *
170  * Why is this?  If a page's completion depends on a number of different BIOs
171  * which can complete in any order (or at the same time) then determining the
172  * status of that page is hard.  See end_buffer_async_read() for the details.
173  * There is no point in duplicating all that complexity.
174  */
175 static void mpage_end_io(struct bio *bio)
176 {
177         if (bio_post_read_required(bio)) {
178                 struct bio_post_read_ctx *ctx = bio->bi_private;
179
180                 ctx->cur_step = STEP_INITIAL;
181                 bio_post_read_processing(ctx);
182                 return;
183         }
184         __read_end_io(bio);
185 }
186
187 static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx)
188 {
189         return fsverity_active(inode) &&
190                idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
191 }
192
193 static void ext4_set_bio_post_read_ctx(struct bio *bio,
194                                        const struct inode *inode,
195                                        pgoff_t first_idx)
196 {
197         unsigned int post_read_steps = 0;
198
199         if (fscrypt_inode_uses_fs_layer_crypto(inode))
200                 post_read_steps |= 1 << STEP_DECRYPT;
201
202         if (ext4_need_verity(inode, first_idx))
203                 post_read_steps |= 1 << STEP_VERITY;
204
205         if (post_read_steps) {
206                 /* Due to the mempool, this never fails. */
207                 struct bio_post_read_ctx *ctx =
208                         mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS);
209
210                 ctx->bio = bio;
211                 ctx->enabled_steps = post_read_steps;
212                 bio->bi_private = ctx;
213         }
214 }
215
216 static inline loff_t ext4_readpage_limit(struct inode *inode)
217 {
218         if (IS_ENABLED(CONFIG_FS_VERITY) &&
219             (IS_VERITY(inode) || ext4_verity_in_progress(inode)))
220                 return inode->i_sb->s_maxbytes;
221
222         return i_size_read(inode);
223 }
224
225 int ext4_mpage_readpages(struct inode *inode,
226                 struct readahead_control *rac, struct page *page)
227 {
228         struct bio *bio = NULL;
229         sector_t last_block_in_bio = 0;
230
231         const unsigned blkbits = inode->i_blkbits;
232         const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
233         const unsigned blocksize = 1 << blkbits;
234         sector_t next_block;
235         sector_t block_in_file;
236         sector_t last_block;
237         sector_t last_block_in_file;
238         sector_t blocks[MAX_BUF_PER_PAGE];
239         unsigned page_block;
240         struct block_device *bdev = inode->i_sb->s_bdev;
241         int length;
242         unsigned relative_block = 0;
243         struct ext4_map_blocks map;
244         unsigned int nr_pages = rac ? readahead_count(rac) : 1;
245
246         map.m_pblk = 0;
247         map.m_lblk = 0;
248         map.m_len = 0;
249         map.m_flags = 0;
250
251         for (; nr_pages; nr_pages--) {
252                 int fully_mapped = 1;
253                 unsigned first_hole = blocks_per_page;
254
255                 if (rac) {
256                         page = readahead_page(rac);
257                         prefetchw(&page->flags);
258                 }
259
260                 if (page_has_buffers(page))
261                         goto confused;
262
263                 block_in_file = next_block =
264                         (sector_t)page->index << (PAGE_SHIFT - blkbits);
265                 last_block = block_in_file + nr_pages * blocks_per_page;
266                 last_block_in_file = (ext4_readpage_limit(inode) +
267                                       blocksize - 1) >> blkbits;
268                 if (last_block > last_block_in_file)
269                         last_block = last_block_in_file;
270                 page_block = 0;
271
272                 /*
273                  * Map blocks using the previous result first.
274                  */
275                 if ((map.m_flags & EXT4_MAP_MAPPED) &&
276                     block_in_file > map.m_lblk &&
277                     block_in_file < (map.m_lblk + map.m_len)) {
278                         unsigned map_offset = block_in_file - map.m_lblk;
279                         unsigned last = map.m_len - map_offset;
280
281                         for (relative_block = 0; ; relative_block++) {
282                                 if (relative_block == last) {
283                                         /* needed? */
284                                         map.m_flags &= ~EXT4_MAP_MAPPED;
285                                         break;
286                                 }
287                                 if (page_block == blocks_per_page)
288                                         break;
289                                 blocks[page_block] = map.m_pblk + map_offset +
290                                         relative_block;
291                                 page_block++;
292                                 block_in_file++;
293                         }
294                 }
295
296                 /*
297                  * Then do more ext4_map_blocks() calls until we are
298                  * done with this page.
299                  */
300                 while (page_block < blocks_per_page) {
301                         if (block_in_file < last_block) {
302                                 map.m_lblk = block_in_file;
303                                 map.m_len = last_block - block_in_file;
304
305                                 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
306                                 set_error_page:
307                                         SetPageError(page);
308                                         zero_user_segment(page, 0,
309                                                           PAGE_SIZE);
310                                         unlock_page(page);
311                                         goto next_page;
312                                 }
313                         }
314                         if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
315                                 fully_mapped = 0;
316                                 if (first_hole == blocks_per_page)
317                                         first_hole = page_block;
318                                 page_block++;
319                                 block_in_file++;
320                                 continue;
321                         }
322                         if (first_hole != blocks_per_page)
323                                 goto confused;          /* hole -> non-hole */
324
325                         /* Contiguous blocks? */
326                         if (page_block && blocks[page_block-1] != map.m_pblk-1)
327                                 goto confused;
328                         for (relative_block = 0; ; relative_block++) {
329                                 if (relative_block == map.m_len) {
330                                         /* needed? */
331                                         map.m_flags &= ~EXT4_MAP_MAPPED;
332                                         break;
333                                 } else if (page_block == blocks_per_page)
334                                         break;
335                                 blocks[page_block] = map.m_pblk+relative_block;
336                                 page_block++;
337                                 block_in_file++;
338                         }
339                 }
340                 if (first_hole != blocks_per_page) {
341                         zero_user_segment(page, first_hole << blkbits,
342                                           PAGE_SIZE);
343                         if (first_hole == 0) {
344                                 if (ext4_need_verity(inode, page->index) &&
345                                     !fsverity_verify_page(page))
346                                         goto set_error_page;
347                                 SetPageUptodate(page);
348                                 unlock_page(page);
349                                 goto next_page;
350                         }
351                 } else if (fully_mapped) {
352                         SetPageMappedToDisk(page);
353                 }
354
355                 /*
356                  * This page will go to BIO.  Do we need to send this
357                  * BIO off first?
358                  */
359                 if (bio && (last_block_in_bio != blocks[0] - 1 ||
360                             !fscrypt_mergeable_bio(bio, inode, next_block))) {
361                 submit_and_realloc:
362                         submit_bio(bio);
363                         bio = NULL;
364                 }
365                 if (bio == NULL) {
366                         /*
367                          * bio_alloc will _always_ be able to allocate a bio if
368                          * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
369                          */
370                         bio = bio_alloc(bdev, bio_max_segs(nr_pages),
371                                         REQ_OP_READ, GFP_KERNEL);
372                         fscrypt_set_bio_crypt_ctx(bio, inode, next_block,
373                                                   GFP_KERNEL);
374                         ext4_set_bio_post_read_ctx(bio, inode, page->index);
375                         bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
376                         bio->bi_end_io = mpage_end_io;
377                         if (rac)
378                                 bio->bi_opf |= REQ_RAHEAD;
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_folio(page_folio(page), ext4_get_block);
400                 else
401                         unlock_page(page);
402         next_page:
403                 if (rac)
404                         put_page(page);
405         }
406         if (bio)
407                 submit_bio(bio);
408         return 0;
409 }
410
411 int __init ext4_init_post_read_processing(void)
412 {
413         bio_post_read_ctx_cache =
414                 kmem_cache_create("ext4_bio_post_read_ctx",
415                                   sizeof(struct bio_post_read_ctx), 0, 0, NULL);
416         if (!bio_post_read_ctx_cache)
417                 goto fail;
418         bio_post_read_ctx_pool =
419                 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,
420                                          bio_post_read_ctx_cache);
421         if (!bio_post_read_ctx_pool)
422                 goto fail_free_cache;
423         return 0;
424
425 fail_free_cache:
426         kmem_cache_destroy(bio_post_read_ctx_cache);
427 fail:
428         return -ENOMEM;
429 }
430
431 void ext4_exit_post_read_processing(void)
432 {
433         mempool_destroy(bio_post_read_ctx_pool);
434         kmem_cache_destroy(bio_post_read_ctx_cache);
435 }