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 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 struct bio *bio = ctx->bio; 110 111 /* 112 * fsverity_verify_bio() may call readpages() again, and although verity 113 * will be disabled for that, decryption may still be needed, causing 114 * another bio_post_read_ctx to be allocated. So to guarantee that 115 * mempool_alloc() never deadlocks we must free the current ctx first. 116 * This is safe because verity is the last post-read step. 117 */ 118 BUILD_BUG_ON(STEP_VERITY + 1 != STEP_MAX); 119 mempool_free(ctx, bio_post_read_ctx_pool); 120 bio->bi_private = NULL; 121 122 fsverity_verify_bio(bio); 123 124 __read_end_io(bio); 125 } 126 127 static void bio_post_read_processing(struct bio_post_read_ctx *ctx) 128 { 129 /* 130 * We use different work queues for decryption and for verity because 131 * verity may require reading metadata pages that need decryption, and 132 * we shouldn't recurse to the same workqueue. 133 */ 134 switch (++ctx->cur_step) { 135 case STEP_DECRYPT: 136 if (ctx->enabled_steps & (1 << STEP_DECRYPT)) { 137 INIT_WORK(&ctx->work, decrypt_work); 138 fscrypt_enqueue_decrypt_work(&ctx->work); 139 return; 140 } 141 ctx->cur_step++; 142 fallthrough; 143 case STEP_VERITY: 144 if (ctx->enabled_steps & (1 << STEP_VERITY)) { 145 INIT_WORK(&ctx->work, verity_work); 146 fsverity_enqueue_verify_work(&ctx->work); 147 return; 148 } 149 ctx->cur_step++; 150 fallthrough; 151 default: 152 __read_end_io(ctx->bio); 153 } 154 } 155 156 static bool bio_post_read_required(struct bio *bio) 157 { 158 return bio->bi_private && !bio->bi_status; 159 } 160 161 /* 162 * I/O completion handler for multipage BIOs. 163 * 164 * The mpage code never puts partial pages into a BIO (except for end-of-file). 165 * If a page does not map to a contiguous run of blocks then it simply falls 166 * back to block_read_full_page(). 167 * 168 * Why is this? If a page's completion depends on a number of different BIOs 169 * which can complete in any order (or at the same time) then determining the 170 * status of that page is hard. See end_buffer_async_read() for the details. 171 * There is no point in duplicating all that complexity. 172 */ 173 static void mpage_end_io(struct bio *bio) 174 { 175 if (bio_post_read_required(bio)) { 176 struct bio_post_read_ctx *ctx = bio->bi_private; 177 178 ctx->cur_step = STEP_INITIAL; 179 bio_post_read_processing(ctx); 180 return; 181 } 182 __read_end_io(bio); 183 } 184 185 static inline bool ext4_need_verity(const struct inode *inode, pgoff_t idx) 186 { 187 return fsverity_active(inode) && 188 idx < DIV_ROUND_UP(inode->i_size, PAGE_SIZE); 189 } 190 191 static void ext4_set_bio_post_read_ctx(struct bio *bio, 192 const struct inode *inode, 193 pgoff_t first_idx) 194 { 195 unsigned int post_read_steps = 0; 196 197 if (fscrypt_inode_uses_fs_layer_crypto(inode)) 198 post_read_steps |= 1 << STEP_DECRYPT; 199 200 if (ext4_need_verity(inode, first_idx)) 201 post_read_steps |= 1 << STEP_VERITY; 202 203 if (post_read_steps) { 204 /* Due to the mempool, this never fails. */ 205 struct bio_post_read_ctx *ctx = 206 mempool_alloc(bio_post_read_ctx_pool, GFP_NOFS); 207 208 ctx->bio = bio; 209 ctx->enabled_steps = post_read_steps; 210 bio->bi_private = ctx; 211 } 212 } 213 214 static inline loff_t ext4_readpage_limit(struct inode *inode) 215 { 216 if (IS_ENABLED(CONFIG_FS_VERITY) && 217 (IS_VERITY(inode) || ext4_verity_in_progress(inode))) 218 return inode->i_sb->s_maxbytes; 219 220 return i_size_read(inode); 221 } 222 223 int ext4_mpage_readpages(struct inode *inode, 224 struct readahead_control *rac, struct page *page) 225 { 226 struct bio *bio = NULL; 227 sector_t last_block_in_bio = 0; 228 229 const unsigned blkbits = inode->i_blkbits; 230 const unsigned blocks_per_page = PAGE_SIZE >> blkbits; 231 const unsigned blocksize = 1 << blkbits; 232 sector_t next_block; 233 sector_t block_in_file; 234 sector_t last_block; 235 sector_t last_block_in_file; 236 sector_t blocks[MAX_BUF_PER_PAGE]; 237 unsigned page_block; 238 struct block_device *bdev = inode->i_sb->s_bdev; 239 int length; 240 unsigned relative_block = 0; 241 struct ext4_map_blocks map; 242 unsigned int nr_pages = rac ? readahead_count(rac) : 1; 243 244 map.m_pblk = 0; 245 map.m_lblk = 0; 246 map.m_len = 0; 247 map.m_flags = 0; 248 249 for (; nr_pages; nr_pages--) { 250 int fully_mapped = 1; 251 unsigned first_hole = blocks_per_page; 252 253 if (rac) { 254 page = readahead_page(rac); 255 prefetchw(&page->flags); 256 } 257 258 if (page_has_buffers(page)) 259 goto confused; 260 261 block_in_file = next_block = 262 (sector_t)page->index << (PAGE_SHIFT - blkbits); 263 last_block = block_in_file + nr_pages * blocks_per_page; 264 last_block_in_file = (ext4_readpage_limit(inode) + 265 blocksize - 1) >> blkbits; 266 if (last_block > last_block_in_file) 267 last_block = last_block_in_file; 268 page_block = 0; 269 270 /* 271 * Map blocks using the previous result first. 272 */ 273 if ((map.m_flags & EXT4_MAP_MAPPED) && 274 block_in_file > map.m_lblk && 275 block_in_file < (map.m_lblk + map.m_len)) { 276 unsigned map_offset = block_in_file - map.m_lblk; 277 unsigned last = map.m_len - map_offset; 278 279 for (relative_block = 0; ; relative_block++) { 280 if (relative_block == last) { 281 /* needed? */ 282 map.m_flags &= ~EXT4_MAP_MAPPED; 283 break; 284 } 285 if (page_block == blocks_per_page) 286 break; 287 blocks[page_block] = map.m_pblk + map_offset + 288 relative_block; 289 page_block++; 290 block_in_file++; 291 } 292 } 293 294 /* 295 * Then do more ext4_map_blocks() calls until we are 296 * done with this page. 297 */ 298 while (page_block < blocks_per_page) { 299 if (block_in_file < last_block) { 300 map.m_lblk = block_in_file; 301 map.m_len = last_block - block_in_file; 302 303 if (ext4_map_blocks(NULL, inode, &map, 0) < 0) { 304 set_error_page: 305 SetPageError(page); 306 zero_user_segment(page, 0, 307 PAGE_SIZE); 308 unlock_page(page); 309 goto next_page; 310 } 311 } 312 if ((map.m_flags & EXT4_MAP_MAPPED) == 0) { 313 fully_mapped = 0; 314 if (first_hole == blocks_per_page) 315 first_hole = page_block; 316 page_block++; 317 block_in_file++; 318 continue; 319 } 320 if (first_hole != blocks_per_page) 321 goto confused; /* hole -> non-hole */ 322 323 /* Contiguous blocks? */ 324 if (page_block && blocks[page_block-1] != map.m_pblk-1) 325 goto confused; 326 for (relative_block = 0; ; relative_block++) { 327 if (relative_block == map.m_len) { 328 /* needed? */ 329 map.m_flags &= ~EXT4_MAP_MAPPED; 330 break; 331 } else if (page_block == blocks_per_page) 332 break; 333 blocks[page_block] = map.m_pblk+relative_block; 334 page_block++; 335 block_in_file++; 336 } 337 } 338 if (first_hole != blocks_per_page) { 339 zero_user_segment(page, first_hole << blkbits, 340 PAGE_SIZE); 341 if (first_hole == 0) { 342 if (ext4_need_verity(inode, page->index) && 343 !fsverity_verify_page(page)) 344 goto set_error_page; 345 SetPageUptodate(page); 346 unlock_page(page); 347 goto next_page; 348 } 349 } else if (fully_mapped) { 350 SetPageMappedToDisk(page); 351 } 352 353 /* 354 * This page will go to BIO. Do we need to send this 355 * BIO off first? 356 */ 357 if (bio && (last_block_in_bio != blocks[0] - 1 || 358 !fscrypt_mergeable_bio(bio, inode, next_block))) { 359 submit_and_realloc: 360 submit_bio(bio); 361 bio = NULL; 362 } 363 if (bio == NULL) { 364 /* 365 * bio_alloc will _always_ be able to allocate a bio if 366 * __GFP_DIRECT_RECLAIM is set, see bio_alloc_bioset(). 367 */ 368 bio = bio_alloc(GFP_KERNEL, bio_max_segs(nr_pages)); 369 fscrypt_set_bio_crypt_ctx(bio, inode, next_block, 370 GFP_KERNEL); 371 ext4_set_bio_post_read_ctx(bio, inode, page->index); 372 bio_set_dev(bio, bdev); 373 bio->bi_iter.bi_sector = blocks[0] << (blkbits - 9); 374 bio->bi_end_io = mpage_end_io; 375 bio_set_op_attrs(bio, REQ_OP_READ, 376 rac ? REQ_RAHEAD : 0); 377 } 378 379 length = first_hole << blkbits; 380 if (bio_add_page(bio, page, length, 0) < length) 381 goto submit_and_realloc; 382 383 if (((map.m_flags & EXT4_MAP_BOUNDARY) && 384 (relative_block == map.m_len)) || 385 (first_hole != blocks_per_page)) { 386 submit_bio(bio); 387 bio = NULL; 388 } else 389 last_block_in_bio = blocks[blocks_per_page - 1]; 390 goto next_page; 391 confused: 392 if (bio) { 393 submit_bio(bio); 394 bio = NULL; 395 } 396 if (!PageUptodate(page)) 397 block_read_full_page(page, ext4_get_block); 398 else 399 unlock_page(page); 400 next_page: 401 if (rac) 402 put_page(page); 403 } 404 if (bio) 405 submit_bio(bio); 406 return 0; 407 } 408 409 int __init ext4_init_post_read_processing(void) 410 { 411 bio_post_read_ctx_cache = 412 kmem_cache_create("ext4_bio_post_read_ctx", 413 sizeof(struct bio_post_read_ctx), 0, 0, NULL); 414 if (!bio_post_read_ctx_cache) 415 goto fail; 416 bio_post_read_ctx_pool = 417 mempool_create_slab_pool(NUM_PREALLOC_POST_READ_CTXS, 418 bio_post_read_ctx_cache); 419 if (!bio_post_read_ctx_pool) 420 goto fail_free_cache; 421 return 0; 422 423 fail_free_cache: 424 kmem_cache_destroy(bio_post_read_ctx_cache); 425 fail: 426 return -ENOMEM; 427 } 428 429 void ext4_exit_post_read_processing(void) 430 { 431 mempool_destroy(bio_post_read_ctx_pool); 432 kmem_cache_destroy(bio_post_read_ctx_cache); 433 } 434