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 52 static struct kmem_cache *bio_post_read_ctx_cache; 53 static mempool_t *bio_post_read_ctx_pool; 54 55 /* postprocessing steps for read bios */ 56 enum bio_post_read_step { 57 STEP_INITIAL = 0, 58 STEP_DECRYPT, 59 STEP_VERITY, 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 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 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); 99 100 fscrypt_decrypt_bio(ctx->bio); 101 102 bio_post_read_processing(ctx); 103 } 104 105 static 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 } 114 115 static 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 } 143 144 static 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 */ 161 static 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 } 172 173 static 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 } 178 179 static 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 } 202 203 static 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 } 211 212 int 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 /* 364 * bio_alloc will _always_ be able to allocate a bio if 365 * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset(). 366 */ 367 bio = bio_alloc(GFP_KERNEL, 368 min_t(int, nr_pages, BIO_MAX_PAGES)); 369 ctx = get_bio_post_read_ctx(inode, bio, page->index); 370 if (IS_ERR(ctx)) { 371 bio_put(bio); 372 bio = NULL; 373 goto set_error_page; 374 } 375 bio_set_dev(bio, bdev); 376 bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9); 377 bio->bi_end_io = mpage_end_io; 378 bio->bi_private = ctx; 379 bio_set_op_attrs(bio, REQ_OP_READ, 380 is_readahead ? REQ_RAHEAD : 0); 381 } 382 383 length = first_hole << blkbits; 384 if (bio_add_page(bio, page, length, 0) < length) 385 goto submit_and_realloc; 386 387 if (((map.m_flags & EXT4_MAP_BOUNDARY) && 388 (relative_block == map.m_len)) || 389 (first_hole != blocks_per_page)) { 390 submit_bio(bio); 391 bio = NULL; 392 } else 393 last_block_in_bio = blocks[blocks_per_page - 1]; 394 goto next_page; 395 confused: 396 if (bio) { 397 submit_bio(bio); 398 bio = NULL; 399 } 400 if (!PageUptodate(page)) 401 block_read_full_page(page, ext4_get_block); 402 else 403 unlock_page(page); 404 next_page: 405 if (pages) 406 put_page(page); 407 } 408 BUG_ON(pages && !list_empty(pages)); 409 if (bio) 410 submit_bio(bio); 411 return 0; 412 } 413 414 int __init ext4_init_post_read_processing(void) 415 { 416 bio_post_read_ctx_cache = 417 kmem_cache_create("ext4_bio_post_read_ctx", 418 sizeof(struct bio_post_read_ctx), 0, 0, NULL); 419 if (!bio_post_read_ctx_cache) 420 goto fail; 421 bio_post_read_ctx_pool = 422 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS, 423 bio_post_read_ctx_cache); 424 if (!bio_post_read_ctx_pool) 425 goto fail_free_cache; 426 return 0; 427 428 fail_free_cache: 429 kmem_cache_destroy(bio_post_read_ctx_cache); 430 fail: 431 return -ENOMEM; 432 } 433 434 void ext4_exit_post_read_processing(void) 435 { 436 mempool_destroy(bio_post_read_ctx_pool); 437 kmem_cache_destroy(bio_post_read_ctx_cache); 438 } 439