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1// SPDX-License-Identifier: GPL-2.02/*3 * Data verification functions, i.e. hooks for ->readahead()4 *5 * Copyright 2019 Google LLC6 */7 8#include "fsverity_private.h"9 10#include <crypto/hash.h>11#include <linux/bio.h>12 13static struct workqueue_struct *fsverity_read_workqueue;14 15/*16 * Returns true if the hash block with index @hblock_idx in the tree, located in17 * @hpage, has already been verified.18 */19static bool is_hash_block_verified(struct fsverity_info *vi, struct page *hpage,20 unsigned long hblock_idx)21{22 unsigned int blocks_per_page;23 unsigned int i;24 25 /*26 * When the Merkle tree block size and page size are the same, then the27 * ->hash_block_verified bitmap isn't allocated, and we use PG_checked28 * to directly indicate whether the page's block has been verified.29 *30 * Using PG_checked also guarantees that we re-verify hash pages that31 * get evicted and re-instantiated from the backing storage, as new32 * pages always start out with PG_checked cleared.33 */34 if (!vi->hash_block_verified)35 return PageChecked(hpage);36 37 /*38 * When the Merkle tree block size and page size differ, we use a bitmap39 * to indicate whether each hash block has been verified.40 *41 * However, we still need to ensure that hash pages that get evicted and42 * re-instantiated from the backing storage are re-verified. To do43 * this, we use PG_checked again, but now it doesn't really mean44 * "checked". Instead, now it just serves as an indicator for whether45 * the hash page is newly instantiated or not. If the page is new, as46 * indicated by PG_checked=0, we clear the bitmap bits for the page's47 * blocks since they are untrustworthy, then set PG_checked=1.48 * Otherwise we return the bitmap bit for the requested block.49 *50 * Multiple threads may execute this code concurrently on the same page.51 * This is safe because we use memory barriers to ensure that if a52 * thread sees PG_checked=1, then it also sees the associated bitmap53 * clearing to have occurred. Also, all writes and their corresponding54 * reads are atomic, and all writes are safe to repeat in the event that55 * multiple threads get into the PG_checked=0 section. (Clearing a56 * bitmap bit again at worst causes a hash block to be verified57 * redundantly. That event should be very rare, so it's not worth using58 * a lock to avoid. Setting PG_checked again has no effect.)59 */60 if (PageChecked(hpage)) {61 /*62 * A read memory barrier is needed here to give ACQUIRE63 * semantics to the above PageChecked() test.64 */65 smp_rmb();66 return test_bit(hblock_idx, vi->hash_block_verified);67 }68 blocks_per_page = vi->tree_params.blocks_per_page;69 hblock_idx = round_down(hblock_idx, blocks_per_page);70 for (i = 0; i < blocks_per_page; i++)71 clear_bit(hblock_idx + i, vi->hash_block_verified);72 /*73 * A write memory barrier is needed here to give RELEASE semantics to74 * the below SetPageChecked() operation.75 */76 smp_wmb();77 SetPageChecked(hpage);78 return false;79}80 81/*82 * Verify a single data block against the file's Merkle tree.83 *84 * In principle, we need to verify the entire path to the root node. However,85 * for efficiency the filesystem may cache the hash blocks. Therefore we need86 * only ascend the tree until an already-verified hash block is seen, and then87 * verify the path to that block.88 *89 * Return: %true if the data block is valid, else %false.90 */91static bool92verify_data_block(struct inode *inode, struct fsverity_info *vi,93 const void *data, u64 data_pos, unsigned long max_ra_pages)94{95 const struct merkle_tree_params *params = &vi->tree_params;96 const unsigned int hsize = params->digest_size;97 int level;98 u8 _want_hash[FS_VERITY_MAX_DIGEST_SIZE];99 const u8 *want_hash;100 u8 real_hash[FS_VERITY_MAX_DIGEST_SIZE];101 /* The hash blocks that are traversed, indexed by level */102 struct {103 /* Page containing the hash block */104 struct page *page;105 /* Mapped address of the hash block (will be within @page) */106 const void *addr;107 /* Index of the hash block in the tree overall */108 unsigned long index;109 /* Byte offset of the wanted hash relative to @addr */110 unsigned int hoffset;111 } hblocks[FS_VERITY_MAX_LEVELS];112 /*113 * The index of the previous level's block within that level; also the114 * index of that block's hash within the current level.115 */116 u64 hidx = data_pos >> params->log_blocksize;117 118 /* Up to 1 + FS_VERITY_MAX_LEVELS pages may be mapped at once */119 BUILD_BUG_ON(1 + FS_VERITY_MAX_LEVELS > KM_MAX_IDX);120 121 if (unlikely(data_pos >= inode->i_size)) {122 /*123 * This can happen in the data page spanning EOF when the Merkle124 * tree block size is less than the page size. The Merkle tree125 * doesn't cover data blocks fully past EOF. But the entire126 * page spanning EOF can be visible to userspace via a mmap, and127 * any part past EOF should be all zeroes. Therefore, we need128 * to verify that any data blocks fully past EOF are all zeroes.129 */130 if (memchr_inv(data, 0, params->block_size)) {131 fsverity_err(inode,132 "FILE CORRUPTED! Data past EOF is not zeroed");133 return false;134 }135 return true;136 }137 138 /*139 * Starting at the leaf level, ascend the tree saving hash blocks along140 * the way until we find a hash block that has already been verified, or141 * until we reach the root.142 */143 for (level = 0; level < params->num_levels; level++) {144 unsigned long next_hidx;145 unsigned long hblock_idx;146 pgoff_t hpage_idx;147 unsigned int hblock_offset_in_page;148 unsigned int hoffset;149 struct page *hpage;150 const void *haddr;151 152 /*153 * The index of the block in the current level; also the index154 * of that block's hash within the next level.155 */156 next_hidx = hidx >> params->log_arity;157 158 /* Index of the hash block in the tree overall */159 hblock_idx = params->level_start[level] + next_hidx;160 161 /* Index of the hash page in the tree overall */162 hpage_idx = hblock_idx >> params->log_blocks_per_page;163 164 /* Byte offset of the hash block within the page */165 hblock_offset_in_page =166 (hblock_idx << params->log_blocksize) & ~PAGE_MASK;167 168 /* Byte offset of the hash within the block */169 hoffset = (hidx << params->log_digestsize) &170 (params->block_size - 1);171 172 hpage = inode->i_sb->s_vop->read_merkle_tree_page(inode,173 hpage_idx, level == 0 ? min(max_ra_pages,174 params->tree_pages - hpage_idx) : 0);175 if (IS_ERR(hpage)) {176 fsverity_err(inode,177 "Error %ld reading Merkle tree page %lu",178 PTR_ERR(hpage), hpage_idx);179 goto error;180 }181 haddr = kmap_local_page(hpage) + hblock_offset_in_page;182 if (is_hash_block_verified(vi, hpage, hblock_idx)) {183 memcpy(_want_hash, haddr + hoffset, hsize);184 want_hash = _want_hash;185 kunmap_local(haddr);186 put_page(hpage);187 goto descend;188 }189 hblocks[level].page = hpage;190 hblocks[level].addr = haddr;191 hblocks[level].index = hblock_idx;192 hblocks[level].hoffset = hoffset;193 hidx = next_hidx;194 }195 196 want_hash = vi->root_hash;197descend:198 /* Descend the tree verifying hash blocks. */199 for (; level > 0; level--) {200 struct page *hpage = hblocks[level - 1].page;201 const void *haddr = hblocks[level - 1].addr;202 unsigned long hblock_idx = hblocks[level - 1].index;203 unsigned int hoffset = hblocks[level - 1].hoffset;204 205 if (fsverity_hash_block(params, inode, haddr, real_hash) != 0)206 goto error;207 if (memcmp(want_hash, real_hash, hsize) != 0)208 goto corrupted;209 /*210 * Mark the hash block as verified. This must be atomic and211 * idempotent, as the same hash block might be verified by212 * multiple threads concurrently.213 */214 if (vi->hash_block_verified)215 set_bit(hblock_idx, vi->hash_block_verified);216 else217 SetPageChecked(hpage);218 memcpy(_want_hash, haddr + hoffset, hsize);219 want_hash = _want_hash;220 kunmap_local(haddr);221 put_page(hpage);222 }223 224 /* Finally, verify the data block. */225 if (fsverity_hash_block(params, inode, data, real_hash) != 0)226 goto error;227 if (memcmp(want_hash, real_hash, hsize) != 0)228 goto corrupted;229 return true;230 231corrupted:232 fsverity_err(inode,233 "FILE CORRUPTED! pos=%llu, level=%d, want_hash=%s:%*phN, real_hash=%s:%*phN",234 data_pos, level - 1,235 params->hash_alg->name, hsize, want_hash,236 params->hash_alg->name, hsize, real_hash);237error:238 for (; level > 0; level--) {239 kunmap_local(hblocks[level - 1].addr);240 put_page(hblocks[level - 1].page);241 }242 return false;243}244 245static bool246verify_data_blocks(struct folio *data_folio, size_t len, size_t offset,247 unsigned long max_ra_pages)248{249 struct inode *inode = data_folio->mapping->host;250 struct fsverity_info *vi = inode->i_verity_info;251 const unsigned int block_size = vi->tree_params.block_size;252 u64 pos = (u64)data_folio->index << PAGE_SHIFT;253 254 if (WARN_ON_ONCE(len <= 0 || !IS_ALIGNED(len | offset, block_size)))255 return false;256 if (WARN_ON_ONCE(!folio_test_locked(data_folio) ||257 folio_test_uptodate(data_folio)))258 return false;259 do {260 void *data;261 bool valid;262 263 data = kmap_local_folio(data_folio, offset);264 valid = verify_data_block(inode, vi, data, pos + offset,265 max_ra_pages);266 kunmap_local(data);267 if (!valid)268 return false;269 offset += block_size;270 len -= block_size;271 } while (len);272 return true;273}274 275/**276 * fsverity_verify_blocks() - verify data in a folio277 * @folio: the folio containing the data to verify278 * @len: the length of the data to verify in the folio279 * @offset: the offset of the data to verify in the folio280 *281 * Verify data that has just been read from a verity file. The data must be282 * located in a pagecache folio that is still locked and not yet uptodate. The283 * length and offset of the data must be Merkle tree block size aligned.284 *285 * Return: %true if the data is valid, else %false.286 */287bool fsverity_verify_blocks(struct folio *folio, size_t len, size_t offset)288{289 return verify_data_blocks(folio, len, offset, 0);290}291EXPORT_SYMBOL_GPL(fsverity_verify_blocks);292 293#ifdef CONFIG_BLOCK294/**295 * fsverity_verify_bio() - verify a 'read' bio that has just completed296 * @bio: the bio to verify297 *298 * Verify the bio's data against the file's Merkle tree. All bio data segments299 * must be aligned to the file's Merkle tree block size. If any data fails300 * verification, then bio->bi_status is set to an error status.301 *302 * This is a helper function for use by the ->readahead() method of filesystems303 * that issue bios to read data directly into the page cache. Filesystems that304 * populate the page cache without issuing bios (e.g. non block-based305 * filesystems) must instead call fsverity_verify_page() directly on each page.306 * All filesystems must also call fsverity_verify_page() on holes.307 */308void fsverity_verify_bio(struct bio *bio)309{310 struct folio_iter fi;311 unsigned long max_ra_pages = 0;312 313 if (bio->bi_opf & REQ_RAHEAD) {314 /*315 * If this bio is for data readahead, then we also do readahead316 * of the first (largest) level of the Merkle tree. Namely,317 * when a Merkle tree page is read, we also try to piggy-back on318 * some additional pages -- up to 1/4 the number of data pages.319 *320 * This improves sequential read performance, as it greatly321 * reduces the number of I/O requests made to the Merkle tree.322 */323 max_ra_pages = bio->bi_iter.bi_size >> (PAGE_SHIFT + 2);324 }325 326 bio_for_each_folio_all(fi, bio) {327 if (!verify_data_blocks(fi.folio, fi.length, fi.offset,328 max_ra_pages)) {329 bio->bi_status = BLK_STS_IOERR;330 break;331 }332 }333}334EXPORT_SYMBOL_GPL(fsverity_verify_bio);335#endif /* CONFIG_BLOCK */336 337/**338 * fsverity_enqueue_verify_work() - enqueue work on the fs-verity workqueue339 * @work: the work to enqueue340 *341 * Enqueue verification work for asynchronous processing.342 */343void fsverity_enqueue_verify_work(struct work_struct *work)344{345 queue_work(fsverity_read_workqueue, work);346}347EXPORT_SYMBOL_GPL(fsverity_enqueue_verify_work);348 349void __init fsverity_init_workqueue(void)350{351 /*352 * Use a high-priority workqueue to prioritize verification work, which353 * blocks reads from completing, over regular application tasks.354 *355 * For performance reasons, don't use an unbound workqueue. Using an356 * unbound workqueue for crypto operations causes excessive scheduler357 * latency on ARM64.358 */359 fsverity_read_workqueue = alloc_workqueue("fsverity_read_queue",360 WQ_HIGHPRI,361 num_online_cpus());362 if (!fsverity_read_workqueue)363 panic("failed to allocate fsverity_read_queue");364}365