diff options
Diffstat (limited to 'fs/verity')
| -rw-r--r-- | fs/verity/Kconfig | 38 | ||||
| -rw-r--r-- | fs/verity/Makefile | 4 | ||||
| -rw-r--r-- | fs/verity/fsverity_private.h | 88 | ||||
| -rw-r--r-- | fs/verity/hash_algs.c | 275 | ||||
| -rw-r--r-- | fs/verity/init.c | 41 |
5 files changed, 446 insertions, 0 deletions
diff --git a/fs/verity/Kconfig b/fs/verity/Kconfig new file mode 100644 index 000000000000..c2bca0b01ecf --- /dev/null +++ b/fs/verity/Kconfig @@ -0,0 +1,38 @@ +# SPDX-License-Identifier: GPL-2.0 + +config FS_VERITY + bool "FS Verity (read-only file-based authenticity protection)" + select CRYPTO + # SHA-256 is selected as it's intended to be the default hash algorithm. + # To avoid bloat, other wanted algorithms must be selected explicitly. + select CRYPTO_SHA256 + help + This option enables fs-verity. fs-verity is the dm-verity + mechanism implemented at the file level. On supported + filesystems (currently EXT4 and F2FS), userspace can use an + ioctl to enable verity for a file, which causes the filesystem + to build a Merkle tree for the file. The filesystem will then + transparently verify any data read from the file against the + Merkle tree. The file is also made read-only. + + This serves as an integrity check, but the availability of the + Merkle tree root hash also allows efficiently supporting + various use cases where normally the whole file would need to + be hashed at once, such as: (a) auditing (logging the file's + hash), or (b) authenticity verification (comparing the hash + against a known good value, e.g. from a digital signature). + + fs-verity is especially useful on large files where not all + the contents may actually be needed. Also, fs-verity verifies + data each time it is paged back in, which provides better + protection against malicious disks vs. an ahead-of-time hash. + + If unsure, say N. + +config FS_VERITY_DEBUG + bool "FS Verity debugging" + depends on FS_VERITY + help + Enable debugging messages related to fs-verity by default. + + Say N unless you are an fs-verity developer. diff --git a/fs/verity/Makefile b/fs/verity/Makefile new file mode 100644 index 000000000000..398f3f85fa18 --- /dev/null +++ b/fs/verity/Makefile @@ -0,0 +1,4 @@ +# SPDX-License-Identifier: GPL-2.0 + +obj-$(CONFIG_FS_VERITY) += hash_algs.o \ + init.o diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h new file mode 100644 index 000000000000..9697aaebb5dc --- /dev/null +++ b/fs/verity/fsverity_private.h @@ -0,0 +1,88 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * fs-verity: read-only file-based authenticity protection + * + * Copyright 2019 Google LLC + */ + +#ifndef _FSVERITY_PRIVATE_H +#define _FSVERITY_PRIVATE_H + +#ifdef CONFIG_FS_VERITY_DEBUG +#define DEBUG +#endif + +#define pr_fmt(fmt) "fs-verity: " fmt + +#include <crypto/sha.h> +#include <linux/fs.h> +#include <uapi/linux/fsverity.h> + +struct ahash_request; + +/* + * Implementation limit: maximum depth of the Merkle tree. For now 8 is plenty; + * it's enough for over U64_MAX bytes of data using SHA-256 and 4K blocks. + */ +#define FS_VERITY_MAX_LEVELS 8 + +/* + * Largest digest size among all hash algorithms supported by fs-verity. + * Currently assumed to be <= size of fsverity_descriptor::root_hash. + */ +#define FS_VERITY_MAX_DIGEST_SIZE SHA256_DIGEST_SIZE + +/* A hash algorithm supported by fs-verity */ +struct fsverity_hash_alg { + struct crypto_ahash *tfm; /* hash tfm, allocated on demand */ + const char *name; /* crypto API name, e.g. sha256 */ + unsigned int digest_size; /* digest size in bytes, e.g. 32 for SHA-256 */ + unsigned int block_size; /* block size in bytes, e.g. 64 for SHA-256 */ +}; + +/* Merkle tree parameters: hash algorithm, initial hash state, and topology */ +struct merkle_tree_params { + const struct fsverity_hash_alg *hash_alg; /* the hash algorithm */ + const u8 *hashstate; /* initial hash state or NULL */ + unsigned int digest_size; /* same as hash_alg->digest_size */ + unsigned int block_size; /* size of data and tree blocks */ + unsigned int hashes_per_block; /* number of hashes per tree block */ + unsigned int log_blocksize; /* log2(block_size) */ + unsigned int log_arity; /* log2(hashes_per_block) */ + unsigned int num_levels; /* number of levels in Merkle tree */ + u64 tree_size; /* Merkle tree size in bytes */ + + /* + * Starting block index for each tree level, ordered from leaf level (0) + * to root level ('num_levels - 1') + */ + u64 level_start[FS_VERITY_MAX_LEVELS]; +}; + +/* hash_algs.c */ + +extern struct fsverity_hash_alg fsverity_hash_algs[]; + +const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode, + unsigned int num); +const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg, + const u8 *salt, size_t salt_size); +int fsverity_hash_page(const struct merkle_tree_params *params, + const struct inode *inode, + struct ahash_request *req, struct page *page, u8 *out); +int fsverity_hash_buffer(const struct fsverity_hash_alg *alg, + const void *data, size_t size, u8 *out); +void __init fsverity_check_hash_algs(void); + +/* init.c */ + +extern void __printf(3, 4) __cold +fsverity_msg(const struct inode *inode, const char *level, + const char *fmt, ...); + +#define fsverity_warn(inode, fmt, ...) \ + fsverity_msg((inode), KERN_WARNING, fmt, ##__VA_ARGS__) +#define fsverity_err(inode, fmt, ...) \ + fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__) + +#endif /* _FSVERITY_PRIVATE_H */ diff --git a/fs/verity/hash_algs.c b/fs/verity/hash_algs.c new file mode 100644 index 000000000000..7df1d67742b8 --- /dev/null +++ b/fs/verity/hash_algs.c @@ -0,0 +1,275 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * fs/verity/hash_algs.c: fs-verity hash algorithms + * + * Copyright 2019 Google LLC + */ + +#include "fsverity_private.h" + +#include <crypto/hash.h> +#include <linux/scatterlist.h> + +/* The hash algorithms supported by fs-verity */ +struct fsverity_hash_alg fsverity_hash_algs[] = { + [FS_VERITY_HASH_ALG_SHA256] = { + .name = "sha256", + .digest_size = SHA256_DIGEST_SIZE, + .block_size = SHA256_BLOCK_SIZE, + }, +}; + +/** + * fsverity_get_hash_alg() - validate and prepare a hash algorithm + * @inode: optional inode for logging purposes + * @num: the hash algorithm number + * + * Get the struct fsverity_hash_alg for the given hash algorithm number, and + * ensure it has a hash transform ready to go. The hash transforms are + * allocated on-demand so that we don't waste resources unnecessarily, and + * because the crypto modules may be initialized later than fs/verity/. + * + * Return: pointer to the hash alg on success, else an ERR_PTR() + */ +const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode, + unsigned int num) +{ + struct fsverity_hash_alg *alg; + struct crypto_ahash *tfm; + int err; + + if (num >= ARRAY_SIZE(fsverity_hash_algs) || + !fsverity_hash_algs[num].name) { + fsverity_warn(inode, "Unknown hash algorithm number: %u", num); + return ERR_PTR(-EINVAL); + } + alg = &fsverity_hash_algs[num]; + + /* pairs with cmpxchg() below */ + tfm = READ_ONCE(alg->tfm); + if (likely(tfm != NULL)) + return alg; + /* + * Using the shash API would make things a bit simpler, but the ahash + * API is preferable as it allows the use of crypto accelerators. + */ + tfm = crypto_alloc_ahash(alg->name, 0, 0); + if (IS_ERR(tfm)) { + if (PTR_ERR(tfm) == -ENOENT) { + fsverity_warn(inode, + "Missing crypto API support for hash algorithm \"%s\"", + alg->name); + return ERR_PTR(-ENOPKG); + } + fsverity_err(inode, + "Error allocating hash algorithm \"%s\": %ld", + alg->name, PTR_ERR(tfm)); + return ERR_CAST(tfm); + } + + err = -EINVAL; + if (WARN_ON(alg->digest_size != crypto_ahash_digestsize(tfm))) + goto err_free_tfm; + if (WARN_ON(alg->block_size != crypto_ahash_blocksize(tfm))) + goto err_free_tfm; + + pr_info("%s using implementation \"%s\"\n", + alg->name, crypto_ahash_driver_name(tfm)); + + /* pairs with READ_ONCE() above */ + if (cmpxchg(&alg->tfm, NULL, tfm) != NULL) + crypto_free_ahash(tfm); + + return alg; + +err_free_tfm: + crypto_free_ahash(tfm); + return ERR_PTR(err); +} + +/** + * fsverity_prepare_hash_state() - precompute the initial hash state + * @alg: hash algorithm + * @salt: a salt which is to be prepended to all data to be hashed + * @salt_size: salt size in bytes, possibly 0 + * + * Return: NULL if the salt is empty, otherwise the kmalloc()'ed precomputed + * initial hash state on success or an ERR_PTR() on failure. + */ +const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg, + const u8 *salt, size_t salt_size) +{ + u8 *hashstate = NULL; + struct ahash_request *req = NULL; + u8 *padded_salt = NULL; + size_t padded_salt_size; + struct scatterlist sg; + DECLARE_CRYPTO_WAIT(wait); + int err; + + if (salt_size == 0) + return NULL; + + hashstate = kmalloc(crypto_ahash_statesize(alg->tfm), GFP_KERNEL); + if (!hashstate) + return ERR_PTR(-ENOMEM); + + req = ahash_request_alloc(alg->tfm, GFP_KERNEL); + if (!req) { + err = -ENOMEM; + goto err_free; + } + + /* + * Zero-pad the salt to the next multiple of the input size of the hash + * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128 + * bytes for SHA-512. This ensures that the hash algorithm won't have + * any bytes buffered internally after processing the salt, thus making + * salted hashing just as fast as unsalted hashing. + */ + padded_salt_size = round_up(salt_size, alg->block_size); + padded_salt = kzalloc(padded_salt_size, GFP_KERNEL); + if (!padded_salt) { + err = -ENOMEM; + goto err_free; + } + memcpy(padded_salt, salt, salt_size); + + sg_init_one(&sg, padded_salt, padded_salt_size); + ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | + CRYPTO_TFM_REQ_MAY_BACKLOG, + crypto_req_done, &wait); + ahash_request_set_crypt(req, &sg, NULL, padded_salt_size); + + err = crypto_wait_req(crypto_ahash_init(req), &wait); + if (err) + goto err_free; + + err = crypto_wait_req(crypto_ahash_update(req), &wait); + if (err) + goto err_free; + + err = crypto_ahash_export(req, hashstate); + if (err) + goto err_free; +out: + ahash_request_free(req); + kfree(padded_salt); + return hashstate; + +err_free: + kfree(hashstate); + hashstate = ERR_PTR(err); + goto out; +} + +/** + * fsverity_hash_page() - hash a single data or hash page + * @params: the Merkle tree's parameters + * @inode: inode for which the hashing is being done + * @req: preallocated hash request + * @page: the page to hash + * @out: output digest, size 'params->digest_size' bytes + * + * Hash a single data or hash block, assuming block_size == PAGE_SIZE. + * The hash is salted if a salt is specified in the Merkle tree parameters. + * + * Return: 0 on success, -errno on failure + */ +int fsverity_hash_page(const struct merkle_tree_params *params, + const struct inode *inode, + struct ahash_request *req, struct page *page, u8 *out) +{ + struct scatterlist sg; + DECLARE_CRYPTO_WAIT(wait); + int err; + + if (WARN_ON(params->block_size != PAGE_SIZE)) + return -EINVAL; + + sg_init_table(&sg, 1); + sg_set_page(&sg, page, PAGE_SIZE, 0); + ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | + CRYPTO_TFM_REQ_MAY_BACKLOG, + crypto_req_done, &wait); + ahash_request_set_crypt(req, &sg, out, PAGE_SIZE); + + if (params->hashstate) { + err = crypto_ahash_import(req, params->hashstate); + if (err) { + fsverity_err(inode, + "Error %d importing hash state", err); + return err; + } + err = crypto_ahash_finup(req); + } else { + err = crypto_ahash_digest(req); + } + + err = crypto_wait_req(err, &wait); + if (err) + fsverity_err(inode, "Error %d computing page hash", err); + return err; +} + +/** + * fsverity_hash_buffer() - hash some data + * @alg: the hash algorithm to use + * @data: the data to hash + * @size: size of data to hash, in bytes + * @out: output digest, size 'alg->digest_size' bytes + * + * Hash some data which is located in physically contiguous memory (i.e. memory + * allocated by kmalloc(), not by vmalloc()). No salt is used. + * + * Return: 0 on success, -errno on failure + */ +int fsverity_hash_buffer(const struct fsverity_hash_alg *alg, + const void *data, size_t size, u8 *out) +{ + struct ahash_request *req; + struct scatterlist sg; + DECLARE_CRYPTO_WAIT(wait); + int err; + + req = ahash_request_alloc(alg->tfm, GFP_KERNEL); + if (!req) + return -ENOMEM; + + sg_init_one(&sg, data, size); + ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_SLEEP | + CRYPTO_TFM_REQ_MAY_BACKLOG, + crypto_req_done, &wait); + ahash_request_set_crypt(req, &sg, out, size); + + err = crypto_wait_req(crypto_ahash_digest(req), &wait); + + ahash_request_free(req); + return err; +} + +void __init fsverity_check_hash_algs(void) +{ + size_t i; + + /* + * Sanity check the hash algorithms (could be a build-time check, but + * they're in an array) + */ + for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) { + const struct fsverity_hash_alg *alg = &fsverity_hash_algs[i]; + + if (!alg->name) + continue; + + BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE); + + /* + * For efficiency, the implementation currently assumes the + * digest and block sizes are powers of 2. This limitation can + * be lifted if the code is updated to handle other values. + */ + BUG_ON(!is_power_of_2(alg->digest_size)); + BUG_ON(!is_power_of_2(alg->block_size)); + } +} diff --git a/fs/verity/init.c b/fs/verity/init.c new file mode 100644 index 000000000000..40076bbe452a --- /dev/null +++ b/fs/verity/init.c @@ -0,0 +1,41 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * fs/verity/init.c: fs-verity module initialization and logging + * + * Copyright 2019 Google LLC + */ + +#include "fsverity_private.h" + +#include <linux/ratelimit.h> + +void fsverity_msg(const struct inode *inode, const char *level, + const char *fmt, ...) +{ + static DEFINE_RATELIMIT_STATE(rs, DEFAULT_RATELIMIT_INTERVAL, + DEFAULT_RATELIMIT_BURST); + struct va_format vaf; + va_list args; + + if (!__ratelimit(&rs)) + return; + + va_start(args, fmt); + vaf.fmt = fmt; + vaf.va = &args; + if (inode) + printk("%sfs-verity (%s, inode %lu): %pV\n", + level, inode->i_sb->s_id, inode->i_ino, &vaf); + else + printk("%sfs-verity: %pV\n", level, &vaf); + va_end(args); +} + +static int __init fsverity_init(void) +{ + fsverity_check_hash_algs(); + + pr_debug("Initialized fs-verity\n"); + return 0; +} +late_initcall(fsverity_init) |