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
51static struct kmem_cache *bio_post_read_ctx_cache;
52static mempool_t *bio_post_read_ctx_pool;
53
54/* postprocessing steps for read bios */
55enum bio_post_read_step {
56	STEP_INITIAL = 0,
57	STEP_DECRYPT,
58	STEP_VERITY,
59	STEP_MAX,
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 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
80static void bio_post_read_processing(struct bio_post_read_ctx *ctx);
81
82static 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
94static 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
116static 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
145static 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 */
162static 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
174static 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
180static 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
203static 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
211int 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_set_error(folio);
293					folio_zero_segment(folio, 0,
294							  folio_size(folio));
295					folio_unlock(folio);
296					goto next_page;
297				}
298			}
299			if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
300				fully_mapped = 0;
301				if (first_hole == blocks_per_page)
302					first_hole = page_block;
303				page_block++;
304				block_in_file++;
305				continue;
306			}
307			if (first_hole != blocks_per_page)
308				goto confused;		/* hole -> non-hole */
309
310			/* Contiguous blocks? */
311			if (page_block && blocks[page_block-1] != map.m_pblk-1)
312				goto confused;
313			for (relative_block = 0; ; relative_block++) {
314				if (relative_block == map.m_len) {
315					/* needed? */
316					map.m_flags &= ~EXT4_MAP_MAPPED;
317					break;
318				} else if (page_block == blocks_per_page)
319					break;
320				blocks[page_block] = map.m_pblk+relative_block;
321				page_block++;
322				block_in_file++;
323			}
324		}
325		if (first_hole != blocks_per_page) {
326			folio_zero_segment(folio, first_hole << blkbits,
327					  folio_size(folio));
328			if (first_hole == 0) {
329				if (ext4_need_verity(inode, folio->index) &&
330				    !fsverity_verify_folio(folio))
331					goto set_error_page;
332				folio_end_read(folio, true);
333				continue;
334			}
335		} else if (fully_mapped) {
336			folio_set_mappedtodisk(folio);
337		}
338
339		/*
340		 * This folio will go to BIO.  Do we need to send this
341		 * BIO off first?
342		 */
343		if (bio && (last_block_in_bio != blocks[0] - 1 ||
344			    !fscrypt_mergeable_bio(bio, inode, next_block))) {
345		submit_and_realloc:
346			submit_bio(bio);
347			bio = NULL;
348		}
349		if (bio == NULL) {
350			/*
351			 * bio_alloc will _always_ be able to allocate a bio if
352			 * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
353			 */
354			bio = bio_alloc(bdev, bio_max_segs(nr_pages),
355					REQ_OP_READ, GFP_KERNEL);
356			fscrypt_set_bio_crypt_ctx(bio, inode, next_block,
357						  GFP_KERNEL);
358			ext4_set_bio_post_read_ctx(bio, inode, folio->index);
359			bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
360			bio->bi_end_io = mpage_end_io;
361			if (rac)
362				bio->bi_opf |= REQ_RAHEAD;
363		}
364
365		length = first_hole << blkbits;
366		if (!bio_add_folio(bio, folio, length, 0))
367			goto submit_and_realloc;
368
369		if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
370		     (relative_block == map.m_len)) ||
371		    (first_hole != blocks_per_page)) {
372			submit_bio(bio);
373			bio = NULL;
374		} else
375			last_block_in_bio = blocks[blocks_per_page - 1];
376		continue;
377	confused:
378		if (bio) {
379			submit_bio(bio);
380			bio = NULL;
381		}
382		if (!folio_test_uptodate(folio))
383			block_read_full_folio(folio, ext4_get_block);
384		else
385			folio_unlock(folio);
386next_page:
387		; /* A label shall be followed by a statement until C23 */
388	}
389	if (bio)
390		submit_bio(bio);
391	return 0;
392}
393
394int __init ext4_init_post_read_processing(void)
395{
396	bio_post_read_ctx_cache = KMEM_CACHE(bio_post_read_ctx, SLAB_RECLAIM_ACCOUNT);
397
398	if (!bio_post_read_ctx_cache)
399		goto fail;
400	bio_post_read_ctx_pool =
401		mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,
402					 bio_post_read_ctx_cache);
403	if (!bio_post_read_ctx_pool)
404		goto fail_free_cache;
405	return 0;
406
407fail_free_cache:
408	kmem_cache_destroy(bio_post_read_ctx_cache);
409fail:
410	return -ENOMEM;
411}
412
413void ext4_exit_post_read_processing(void)
414{
415	mempool_destroy(bio_post_read_ctx_pool);
416	kmem_cache_destroy(bio_post_read_ctx_cache);
417}
418