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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 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 #include <linux/cleancache.h>
47 
48 #include "ext4.h"
49 #include <trace/events/android_fs.h>
50 
51 #define NUM_PREALLOC_POST_READ_CTXS	128
52 
53 static struct kmem_cache *bio_post_read_ctx_cache;
54 static mempool_t *bio_post_read_ctx_pool;
55 
56 /* postprocessing steps for read bios */
57 enum bio_post_read_step {
58 	STEP_INITIAL = 0,
59 	STEP_DECRYPT,
60 	STEP_VERITY,
61 	STEP_MAX,
62 };
63 
64 struct bio_post_read_ctx {
65 	struct bio *bio;
66 	struct work_struct work;
67 	unsigned int cur_step;
68 	unsigned int enabled_steps;
69 };
70 
__read_end_io(struct bio * bio)71 static void __read_end_io(struct bio *bio)
72 {
73 	struct page *page;
74 	struct bio_vec *bv;
75 	struct bvec_iter_all iter_all;
76 
77 	bio_for_each_segment_all(bv, bio, iter_all) {
78 		page = bv->bv_page;
79 
80 		/* PG_error was set if any post_read step failed */
81 		if (bio->bi_status || PageError(page)) {
82 			ClearPageUptodate(page);
83 			/* will re-read again later */
84 			ClearPageError(page);
85 		} else {
86 			SetPageUptodate(page);
87 		}
88 		unlock_page(page);
89 	}
90 	if (bio->bi_private)
91 		mempool_free(bio->bi_private, bio_post_read_ctx_pool);
92 	bio_put(bio);
93 }
94 
95 static void bio_post_read_processing(struct bio_post_read_ctx *ctx);
96 
decrypt_work(struct work_struct * work)97 static void decrypt_work(struct work_struct *work)
98 {
99 	struct bio_post_read_ctx *ctx =
100 		container_of(work, struct bio_post_read_ctx, work);
101 
102 	fscrypt_decrypt_bio(ctx->bio);
103 
104 	bio_post_read_processing(ctx);
105 }
106 
verity_work(struct work_struct * work)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 readpages() 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 
bio_post_read_processing(struct bio_post_read_ctx * ctx)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 
bio_post_read_required(struct bio * bio)158 static bool bio_post_read_required(struct bio *bio)
159 {
160 	return bio->bi_private && !bio->bi_status;
161 }
162 
163 static void
ext4_trace_read_completion(struct bio * bio)164 ext4_trace_read_completion(struct bio *bio)
165 {
166 	struct page *first_page = bio->bi_io_vec[0].bv_page;
167 
168 	if (first_page != NULL)
169 		trace_android_fs_dataread_end(first_page->mapping->host,
170 					      page_offset(first_page),
171 					      bio->bi_iter.bi_size);
172 }
173 
174 /*
175  * I/O completion handler for multipage BIOs.
176  *
177  * The mpage code never puts partial pages into a BIO (except for end-of-file).
178  * If a page does not map to a contiguous run of blocks then it simply falls
179  * back to block_read_full_page().
180  *
181  * Why is this?  If a page's completion depends on a number of different BIOs
182  * which can complete in any order (or at the same time) then determining the
183  * status of that page is hard.  See end_buffer_async_read() for the details.
184  * There is no point in duplicating all that complexity.
185  */
mpage_end_io(struct bio * bio)186 static void mpage_end_io(struct bio *bio)
187 {
188 	if (trace_android_fs_dataread_start_enabled())
189 		ext4_trace_read_completion(bio);
190 
191 	if (bio_post_read_required(bio)) {
192 		struct bio_post_read_ctx *ctx = bio->bi_private;
193 
194 		ctx->cur_step = STEP_INITIAL;
195 		bio_post_read_processing(ctx);
196 		return;
197 	}
198 	__read_end_io(bio);
199 }
200 
ext4_need_verity(const struct inode * inode,pgoff_t idx)201 static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx)
202 {
203 	return fsverity_active(inode) &&
204 	       idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE);
205 }
206 
ext4_set_bio_post_read_ctx(struct bio * bio,const struct inode * inode,pgoff_t first_idx)207 static void ext4_set_bio_post_read_ctx(struct bio *bio,
208 				       const struct inode *inode,
209 				       pgoff_t first_idx)
210 {
211 	unsigned int post_read_steps = 0;
212 
213 	if (fscrypt_inode_uses_fs_layer_crypto(inode))
214 		post_read_steps |= 1 << STEP_DECRYPT;
215 
216 	if (ext4_need_verity(inode, first_idx))
217 		post_read_steps |= 1 << STEP_VERITY;
218 
219 	if (post_read_steps) {
220 		/* Due to the mempool, this never fails. */
221 		struct bio_post_read_ctx *ctx =
222 			mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS);
223 
224 		ctx->bio = bio;
225 		ctx->enabled_steps = post_read_steps;
226 		bio->bi_private = ctx;
227 	}
228 }
229 
ext4_readpage_limit(struct inode * inode)230 static inline loff_t ext4_readpage_limit(struct inode *inode)
231 {
232 	if (IS_ENABLED(CONFIG_FS_VERITY) &&
233 	    (IS_VERITY(inode) || ext4_verity_in_progress(inode)))
234 		return inode->i_sb->s_maxbytes;
235 
236 	return i_size_read(inode);
237 }
238 
239 static void
ext4_submit_bio_read(struct bio * bio)240 ext4_submit_bio_read(struct bio *bio)
241 {
242 	if (trace_android_fs_dataread_start_enabled()) {
243 		struct page *first_page = bio->bi_io_vec[0].bv_page;
244 
245 		if (first_page != NULL) {
246 			char *path, pathbuf[MAX_TRACE_PATHBUF_LEN];
247 
248 			path = android_fstrace_get_pathname(pathbuf,
249 						    MAX_TRACE_PATHBUF_LEN,
250 						    first_page->mapping->host);
251 			trace_android_fs_dataread_start(
252 				first_page->mapping->host,
253 				page_offset(first_page),
254 				bio->bi_iter.bi_size,
255 				current->pid,
256 				path,
257 				current->comm);
258 		}
259 	}
260 	submit_bio(bio);
261 }
262 
ext4_mpage_readpages(struct inode * inode,struct readahead_control * rac,struct page * page)263 int ext4_mpage_readpages(struct inode *inode,
264 		struct readahead_control *rac, struct page *page)
265 {
266 	struct bio *bio = NULL;
267 	sector_t last_block_in_bio = 0;
268 
269 	const unsigned blkbits = inode->i_blkbits;
270 	const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
271 	const unsigned blocksize = 1 << blkbits;
272 	sector_t next_block;
273 	sector_t block_in_file;
274 	sector_t last_block;
275 	sector_t last_block_in_file;
276 	sector_t blocks[MAX_BUF_PER_PAGE];
277 	unsigned page_block;
278 	struct block_device *bdev = inode->i_sb->s_bdev;
279 	int length;
280 	unsigned relative_block = 0;
281 	struct ext4_map_blocks map;
282 	unsigned int nr_pages = rac ? readahead_count(rac) : 1;
283 
284 	map.m_pblk = 0;
285 	map.m_lblk = 0;
286 	map.m_len = 0;
287 	map.m_flags = 0;
288 
289 	for (; nr_pages; nr_pages--) {
290 		int fully_mapped = 1;
291 		unsigned first_hole = blocks_per_page;
292 
293 		if (rac) {
294 			page = readahead_page(rac);
295 			prefetchw(&page->flags);
296 		}
297 
298 		if (page_has_buffers(page))
299 			goto confused;
300 
301 		block_in_file = next_block =
302 			(sector_t)page->index << (PAGE_SHIFT - blkbits);
303 		last_block = block_in_file + nr_pages * blocks_per_page;
304 		last_block_in_file = (ext4_readpage_limit(inode) +
305 				      blocksize - 1) >> blkbits;
306 		if (last_block > last_block_in_file)
307 			last_block = last_block_in_file;
308 		page_block = 0;
309 
310 		/*
311 		 * Map blocks using the previous result first.
312 		 */
313 		if ((map.m_flags & EXT4_MAP_MAPPED) &&
314 		    block_in_file > map.m_lblk &&
315 		    block_in_file < (map.m_lblk + map.m_len)) {
316 			unsigned map_offset = block_in_file - map.m_lblk;
317 			unsigned last = map.m_len - map_offset;
318 
319 			for (relative_block = 0; ; relative_block++) {
320 				if (relative_block == last) {
321 					/* needed? */
322 					map.m_flags &= ~EXT4_MAP_MAPPED;
323 					break;
324 				}
325 				if (page_block == blocks_per_page)
326 					break;
327 				blocks[page_block] = map.m_pblk + map_offset +
328 					relative_block;
329 				page_block++;
330 				block_in_file++;
331 			}
332 		}
333 
334 		/*
335 		 * Then do more ext4_map_blocks() calls until we are
336 		 * done with this page.
337 		 */
338 		while (page_block < blocks_per_page) {
339 			if (block_in_file < last_block) {
340 				map.m_lblk = block_in_file;
341 				map.m_len = last_block - block_in_file;
342 
343 				if (ext4_map_blocks(NULL, inode, &map, 0) < 0) {
344 				set_error_page:
345 					SetPageError(page);
346 					zero_user_segment(page, 0,
347 							  PAGE_SIZE);
348 					unlock_page(page);
349 					goto next_page;
350 				}
351 			}
352 			if ((map.m_flags & EXT4_MAP_MAPPED) == 0) {
353 				fully_mapped = 0;
354 				if (first_hole == blocks_per_page)
355 					first_hole = page_block;
356 				page_block++;
357 				block_in_file++;
358 				continue;
359 			}
360 			if (first_hole != blocks_per_page)
361 				goto confused;		/* hole -> non-hole */
362 
363 			/* Contiguous blocks? */
364 			if (page_block && blocks[page_block-1] != map.m_pblk-1)
365 				goto confused;
366 			for (relative_block = 0; ; relative_block++) {
367 				if (relative_block == map.m_len) {
368 					/* needed? */
369 					map.m_flags &= ~EXT4_MAP_MAPPED;
370 					break;
371 				} else if (page_block == blocks_per_page)
372 					break;
373 				blocks[page_block] = map.m_pblk+relative_block;
374 				page_block++;
375 				block_in_file++;
376 			}
377 		}
378 		if (first_hole != blocks_per_page) {
379 			zero_user_segment(page, first_hole << blkbits,
380 					  PAGE_SIZE);
381 			if (first_hole == 0) {
382 				if (ext4_need_verity(inode, page->index) &&
383 				    !fsverity_verify_page(page))
384 					goto set_error_page;
385 				SetPageUptodate(page);
386 				unlock_page(page);
387 				goto next_page;
388 			}
389 		} else if (fully_mapped) {
390 			SetPageMappedToDisk(page);
391 		}
392 		if (fully_mapped && blocks_per_page == 1 &&
393 		    !PageUptodate(page) && cleancache_get_page(page) == 0) {
394 			SetPageUptodate(page);
395 			goto confused;
396 		}
397 
398 		/*
399 		 * This page will go to BIO.  Do we need to send this
400 		 * BIO off first?
401 		 */
402 		if (bio && (last_block_in_bio != blocks[0] - 1 ||
403 			    !fscrypt_mergeable_bio(bio, inode, next_block))) {
404 		submit_and_realloc:
405 			ext4_submit_bio_read(bio);
406 			bio = NULL;
407 		}
408 		if (bio == NULL) {
409 			/*
410 			 * bio_alloc will _always_ be able to allocate a bio if
411 			 * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset().
412 			 */
413 			bio = bio_alloc(GFP_KERNEL,
414 				min_t(int, nr_pages, BIO_MAX_PAGES));
415 			fscrypt_set_bio_crypt_ctx(bio, inode, next_block,
416 						  GFP_KERNEL);
417 			ext4_set_bio_post_read_ctx(bio, inode, page->index);
418 			bio_set_dev(bio, bdev);
419 			bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9);
420 			bio->bi_end_io = mpage_end_io;
421 			bio_set_op_attrs(bio, REQ_OP_READ,
422 						rac ? REQ_RAHEAD : 0);
423 		}
424 
425 		length = first_hole << blkbits;
426 		if (bio_add_page(bio, page, length, 0) < length)
427 			goto submit_and_realloc;
428 
429 		if (((map.m_flags & EXT4_MAP_BOUNDARY) &&
430 		     (relative_block == map.m_len)) ||
431 		    (first_hole != blocks_per_page)) {
432 			ext4_submit_bio_read(bio);
433 			bio = NULL;
434 		} else
435 			last_block_in_bio = blocks[blocks_per_page - 1];
436 		goto next_page;
437 	confused:
438 		if (bio) {
439 			ext4_submit_bio_read(bio);
440 			bio = NULL;
441 		}
442 		if (!PageUptodate(page))
443 			block_read_full_page(page, ext4_get_block);
444 		else
445 			unlock_page(page);
446 	next_page:
447 		if (rac)
448 			put_page(page);
449 	}
450 	if (bio)
451 		ext4_submit_bio_read(bio);
452 	return 0;
453 }
454 
ext4_init_post_read_processing(void)455 int __init ext4_init_post_read_processing(void)
456 {
457 	bio_post_read_ctx_cache =
458 		kmem_cache_create("ext4_bio_post_read_ctx",
459 				  sizeof(struct bio_post_read_ctx), 0, 0, NULL);
460 	if (!bio_post_read_ctx_cache)
461 		goto fail;
462 	bio_post_read_ctx_pool =
463 		mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS,
464 					 bio_post_read_ctx_cache);
465 	if (!bio_post_read_ctx_pool)
466 		goto fail_free_cache;
467 	return 0;
468 
469 fail_free_cache:
470 	kmem_cache_destroy(bio_post_read_ctx_cache);
471 fail:
472 	return -ENOMEM;
473 }
474 
ext4_exit_post_read_processing(void)475 void ext4_exit_post_read_processing(void)
476 {
477 	mempool_destroy(bio_post_read_ctx_pool);
478 	kmem_cache_destroy(bio_post_read_ctx_cache);
479 }
480