[PATCH v2 02/12] fs-verity: add setup code, UAPI, and Kconfig

Eric Biggers
2018-11-01T22:55:26Z

From: Eric Biggers <ebiggers@google.com>

Add the beginnings of fs-verity support, including:

- The fs-verity Kconfig option (CONFIG_FS_VERITY)
- The fs-verity UAPI declarations (uapi/linux/fsverity.h)
- The internal API header for filesystems to use (linux/fsverity.h)
- The "setup" code which parses the fs-verity descriptor to create an
fsverity_info structure that is attached to the in-memory inode; this
structure describes the Merkle tree properties and contains the file
measurement. This is called from the ->open() and ->getattr() hooks.
- Hash algorithm management; initially supporting SHA-256 only.

The actual ->readpages() data verification, the ioctl implementations,
ext4 and f2fs support, and other functionality comes in later patches.

For more information about fs-verity, see the documentation file
Documentation/filesystems/fsverity.rst.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
Documentation/ioctl/ioctl-number.txt | 1 +
fs/Kconfig | 2 +
fs/Makefile | 1 +
fs/verity/Kconfig | 35 ++
fs/verity/Makefile | 3 +
fs/verity/fsverity_private.h | 98 ++++
fs/verity/hash_algs.c | 106 ++++
fs/verity/setup.c | 823 +++++++++++++++++++++++++++
include/linux/fs.h | 9 +
include/linux/fsverity.h | 62 ++
include/uapi/linux/fsverity.h | 86 +++
11 files changed, 1226 insertions(+)
create mode 100644 fs/verity/Kconfig
create mode 100644 fs/verity/Makefile
create mode 100644 fs/verity/fsverity_private.h
create mode 100644 fs/verity/hash_algs.c
create mode 100644 fs/verity/setup.c
create mode 100644 include/linux/fsverity.h
create mode 100644 include/uapi/linux/fsverity.h

diff --git a/Documentation/ioctl/ioctl-number.txt b/Documentation/ioctl/ioctl-number.txt
index af6f6ba1fe804..e9ab862adbf90 100644
--- a/Documentation/ioctl/ioctl-number.txt
+++ b/Documentation/ioctl/ioctl-number.txt
@@ -224,6 +224,7 @@ Code Seq#(hex) Include File Comments
'f' 00-0F fs/ext4/ext4.h conflict!
'f' 00-0F linux/fs.h conflict!
'f' 00-0F fs/ocfs2/ocfs2_fs.h conflict!
+'f' 81-8F linux/fsverity.h
'g' 00-0F linux/usb/gadgetfs.h
'g' 20-2F linux/usb/g_printer.h
'h' 00-7F conflict! Charon filesystem
diff --git a/fs/Kconfig b/fs/Kconfig
index ac474a61be379..ddadc4e999429 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -105,6 +105,8 @@ config MANDATORY_FILE_LOCKING

source "fs/crypto/Kconfig"

+source "fs/verity/Kconfig"
+
source "fs/notify/Kconfig"

source "fs/quota/Kconfig"
diff --git a/fs/Makefile b/fs/Makefile
index 293733f61594b..10b37f651ffde 100644
--- a/fs/Makefile
+++ b/fs/Makefile
@@ -32,6 +32,7 @@ obj-$(CONFIG_USERFAULTFD) += userfaultfd.o
obj-$(CONFIG_AIO) += aio.o
obj-$(CONFIG_FS_DAX) += dax.o
obj-$(CONFIG_FS_ENCRYPTION) += crypto/
+obj-$(CONFIG_FS_VERITY) += verity/
obj-$(CONFIG_FILE_LOCKING) += locks.o
obj-$(CONFIG_COMPAT) += compat.o compat_ioctl.o
obj-$(CONFIG_BINFMT_AOUT) += binfmt_aout.o
diff --git a/fs/verity/Kconfig b/fs/verity/Kconfig
new file mode 100644
index 0000000000000..102c46ebe275f
--- /dev/null
+++ b/fs/verity/Kconfig
@@ -0,0 +1,35 @@
+config FS_VERITY
+ tristate "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, userspace can append a Merkle tree (hash tree) to
+ a file, then enable fs-verity on 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 0000000000000..39e123805c827
--- /dev/null
+++ b/fs/verity/Makefile
@@ -0,0 +1,3 @@
+obj-$(CONFIG_FS_VERITY) += fsverity.o
+
+fsverity-y := hash_algs.o setup.o
diff --git a/fs/verity/fsverity_private.h b/fs/verity/fsverity_private.h
new file mode 100644
index 0000000000000..acc29825a0ed7
--- /dev/null
+++ b/fs/verity/fsverity_private.h
@@ -0,0 +1,98 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * fs-verity: read-only file-based authenticity protection
+ *
+ * Copyright 2018 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>
+#define __FS_HAS_VERITY 1
+#include <linux/fsverity.h>
+
+/*
+ * Maximum depth of the Merkle tree. Up to 64 levels are theoretically possible
+ * with a very small block size, but we'd like to limit stack usage during
+ * verification, and in practice this is plenty. E.g., with SHA-256 and 4K
+ * blocks, a file with size UINT64_MAX bytes needs just 8 levels.
+ */
+#define FS_VERITY_MAX_LEVELS 16
+
+/*
+ * Largest digest size among all hash algorithms supported by fs-verity. This
+ * can be increased if needed.
+ */
+#define FS_VERITY_MAX_DIGEST_SIZE SHA256_DIGEST_SIZE
+
+/* A hash algorithm supported by fs-verity */
+struct fsverity_hash_alg {
+ struct crypto_ahash *tfm; /* allocated on demand */
+ const char *name;
+ unsigned int digest_size;
+ bool cryptographic;
+};
+
+/**
+ * fsverity_info - cached verity metadata for an inode
+ *
+ * When a verity file is first opened, an instance of this struct is allocated
+ * and stored in ->i_verity_info. It caches various values from the verity
+ * metadata, such as the tree topology and the root hash, which are needed to
+ * efficiently verify data read from the file. Once created, it remains until
+ * the inode is evicted.
+ *
+ * (The tree pages themselves are not cached here, though they may be cached in
+ * the inode's page cache.)
+ */
+struct fsverity_info {
+ const struct fsverity_hash_alg *hash_alg; /* hash algorithm */
+ u8 block_bits; /* log2(block size) */
+ u8 log_arity; /* log2(hashes per hash block) */
+ u8 depth; /* num levels in the Merkle tree */
+ u8 *hashstate; /* salted initial hash state */
+ loff_t data_i_size; /* original file size */
+ loff_t metadata_end; /* offset to end of verity metadata */
+ u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE]; /* Merkle tree root hash */
+ u8 measurement[FS_VERITY_MAX_DIGEST_SIZE]; /* file measurement */
+ bool have_root_hash; /* have root hash from disk? */
+
+ /* Starting blocks for each tree level. 'depth-1' is the root level. */
+ u64 hash_lvl_region_idx[FS_VERITY_MAX_LEVELS];
+};
+
+/* hash_algs.c */
+extern struct fsverity_hash_alg fsverity_hash_algs[];
+const struct fsverity_hash_alg *fsverity_get_hash_alg(unsigned int num);
+void __init fsverity_check_hash_algs(void);
+void __exit fsverity_exit_hash_algs(void);
+
+/* setup.c */
+struct page *fsverity_read_metadata_page(struct inode *inode, pgoff_t index);
+struct fsverity_info *create_fsverity_info(struct inode *inode, bool enabling);
+void free_fsverity_info(struct fsverity_info *vi);
+
+static inline struct fsverity_info *get_fsverity_info(const struct inode *inode)
+{
+ /* pairs with cmpxchg_release() in set_fsverity_info() */
+ return smp_load_acquire(&inode->i_verity_info);
+}
+
+static inline bool set_fsverity_info(struct inode *inode,
+ struct fsverity_info *vi)
+{
+ /* Make sure the in-memory i_size is set to the data i_size */
+ i_size_write(inode, vi->data_i_size);
+
+ /* pairs with smp_load_acquire() in get_fsverity_info() */
+ return cmpxchg_release(&inode->i_verity_info, NULL, vi) == NULL;
+}
+
+#endif /* _FSVERITY_PRIVATE_H */
diff --git a/fs/verity/hash_algs.c b/fs/verity/hash_algs.c
new file mode 100644
index 0000000000000..9c19c9553f120
--- /dev/null
+++ b/fs/verity/hash_algs.c
@@ -0,0 +1,106 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fs/verity/hash_algs.c: fs-verity hash algorithm management
+ *
+ * Copyright 2018 Google LLC
+ *
+ * Written by Eric Biggers.
+ */
+
+#include "fsverity_private.h"
+
+#include <crypto/hash.h>
+
+/* The list of hash algorithms supported by fs-verity */
+struct fsverity_hash_alg fsverity_hash_algs[] = {
+ [FS_VERITY_ALG_SHA256] = {
+ .name = "sha256",
+ .digest_size = 32,
+ .cryptographic = true,
+ },
+};
+
+/*
+ * Translate the given fs-verity hash algorithm number into a struct describing
+ * the algorithm, and ensure it has a hash transform ready to go. The hash
+ * transforms are allocated on-demand firstly to not waste resources when they
+ * aren't needed, and secondly because the fs-verity module may be loaded
+ * earlier than the needed crypto modules.
+ */
+const struct fsverity_hash_alg *fsverity_get_hash_alg(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].digest_size) {
+ pr_warn("Unknown hash algorithm: %u\n", num);
+ return ERR_PTR(-EINVAL);
+ }
+ alg = &fsverity_hash_algs[num];
+retry:
+ /* pairs with cmpxchg_release() below */
+ tfm = smp_load_acquire(&alg->tfm);
+ if (tfm)
+ 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)
+ pr_warn("Algorithm %u (%s) is unavailable\n",
+ num, alg->name);
+ else
+ pr_warn("Error allocating algorithm %u (%s): %ld\n",
+ num, 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;
+
+ pr_info("%s using implementation \"%s\"\n", alg->name,
+ crypto_hash_alg_common(tfm)->base.cra_driver_name);
+
+ /* pairs with smp_load_acquire() above */
+ if (cmpxchg_release(&alg->tfm, NULL, tfm) != NULL) {
+ crypto_free_ahash(tfm);
+ goto retry;
+ }
+
+ return alg;
+
+err_free_tfm:
+ crypto_free_ahash(tfm);
+ return ERR_PTR(err);
+}
+
+void __init fsverity_check_hash_algs(void)
+{
+ int i;
+
+ /*
+ * Sanity check the digest sizes (could be a build-time check, but
+ * they're in an array)
+ */
+ for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) {
+ struct fsverity_hash_alg *alg = &fsverity_hash_algs[i];
+
+ if (!alg->digest_size)
+ continue;
+ BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE);
+ BUG_ON(!is_power_of_2(alg->digest_size));
+ }
+}
+
+void __exit fsverity_exit_hash_algs(void)
+{
+ int i;
+
+ for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++)
+ crypto_free_ahash(fsverity_hash_algs[i].tfm);
+}
diff --git a/fs/verity/setup.c b/fs/verity/setup.c
new file mode 100644
index 0000000000000..925970fbe084d
--- /dev/null
+++ b/fs/verity/setup.c
@@ -0,0 +1,823 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fs/verity/setup.c: fs-verity module initialization and descriptor parsing
+ *
+ * Copyright 2018 Google LLC
+ *
+ * Originally written by Jaegeuk Kim and Michael Halcrow;
+ * heavily rewritten by Eric Biggers.
+ */
+
+#include "fsverity_private.h"
+
+#include <crypto/hash.h>
+#include <linux/highmem.h>
+#include <linux/list_sort.h>
+#include <linux/module.h>
+#include <linux/pagemap.h>
+#include <linux/scatterlist.h>
+#include <linux/vmalloc.h>
+
+static struct kmem_cache *fsverity_info_cachep;
+
+static void dump_fsverity_descriptor(const struct fsverity_descriptor *desc)
+{
+ pr_debug("magic = %.*s\n", (int)sizeof(desc->magic), desc->magic);
+ pr_debug("major_version = %u\n", desc->major_version);
+ pr_debug("minor_version = %u\n", desc->minor_version);
+ pr_debug("log_data_blocksize = %u\n", desc->log_data_blocksize);
+ pr_debug("log_tree_blocksize = %u\n", desc->log_tree_blocksize);
+ pr_debug("data_algorithm = %u\n", le16_to_cpu(desc->data_algorithm));
+ pr_debug("tree_algorithm = %u\n", le16_to_cpu(desc->tree_algorithm));
+ pr_debug("flags = %#x\n", le32_to_cpu(desc->flags));
+ pr_debug("orig_file_size = %llu\n", le64_to_cpu(desc->orig_file_size));
+ pr_debug("auth_ext_count = %u\n", le16_to_cpu(desc->auth_ext_count));
+}
+
+/* Precompute the salted initial hash state */
+static int set_salt(struct fsverity_info *vi, const u8 *salt, size_t saltlen)
+{
+ struct crypto_ahash *tfm = vi->hash_alg->tfm;
+ struct ahash_request *req;
+ unsigned int reqsize = sizeof(*req) + crypto_ahash_reqsize(tfm);
+ struct scatterlist sg;
+ DECLARE_CRYPTO_WAIT(wait);
+ u8 *saltbuf;
+ int err;
+
+ vi->hashstate = kmalloc(crypto_ahash_statesize(tfm), GFP_KERNEL);
+ if (!vi->hashstate)
+ return -ENOMEM;
+ /* On error, vi->hashstate is freed by free_fsverity_info() */
+
+ /*
+ * Allocate a hash request buffer. Also reserve space for a copy of
+ * the salt, since the given 'salt' may point into vmap'ed memory, so
+ * sg_init_one() may not work on it.
+ */
+ req = kmalloc(reqsize + saltlen, GFP_KERNEL);
+ if (!req)
+ return -ENOMEM;
+ saltbuf = (u8 *)req + reqsize;
+ memcpy(saltbuf, salt, saltlen);
+ sg_init_one(&sg, saltbuf, saltlen);
+
+ ahash_request_set_tfm(req, tfm);
+ 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, saltlen);
+
+ err = crypto_wait_req(crypto_ahash_init(req), &wait);
+ if (err)
+ goto out;
+ err = crypto_wait_req(crypto_ahash_update(req), &wait);
+ if (err)
+ goto out;
+ err = crypto_ahash_export(req, vi->hashstate);
+out:
+ kfree(req);
+ return err;
+}
+
+/*
+ * Copy in the root hash stored on disk.
+ *
+ * Note that the root hash could be computed by hashing the root block of the
+ * Merkle tree. But it works out a bit simpler to store the hash separately;
+ * then it gets included in the file measurement without special-casing it, and
+ * the root block gets verified on the ->readpages() path like the other blocks.
+ */
+static int parse_root_hash_extension(struct fsverity_info *vi,
+ const void *hash, size_t size)
+{
+ const struct fsverity_hash_alg *alg = vi->hash_alg;
+
+ if (vi->have_root_hash) {
+ pr_warn("Multiple root hashes were found!\n");
+ return -EINVAL;
+ }
+ if (size != alg->digest_size) {
+ pr_warn("Wrong root hash size; got %zu bytes, but expected %u for hash algorithm %s\n",
+ size, alg->digest_size, alg->name);
+ return -EINVAL;
+ }
+ memcpy(vi->root_hash, hash, size);
+ vi->have_root_hash = true;
+ pr_debug("Root hash: %s:%*phN\n", alg->name,
+ alg->digest_size, vi->root_hash);
+ return 0;
+}
+
+static int parse_salt_extension(struct fsverity_info *vi,
+ const void *salt, size_t saltlen)
+{
+ if (vi->hashstate) {
+ pr_warn("Multiple salts were found!\n");
+ return -EINVAL;
+ }
+ return set_salt(vi, salt, saltlen);
+}
+
+/* The available types of extensions (variable-length metadata items) */
+static const struct extension_type {
+ int (*parse)(struct fsverity_info *vi, const void *_ext,
+ size_t extra_len);
+ size_t base_len; /* length of fixed-size part of payload, if any */
+ bool unauthenticated; /* true if not included in file measurement */
+} extension_types[] = {
+ [FS_VERITY_EXT_ROOT_HASH] = {
+ .parse = parse_root_hash_extension,
+ },
+ [FS_VERITY_EXT_SALT] = {
+ .parse = parse_salt_extension,
+ },
+};
+
+static int do_parse_extensions(struct fsverity_info *vi,
+ const struct fsverity_extension **ext_hdr_p,
+ const void *end, int count, bool authenticated)
+{
+ const struct fsverity_extension *ext_hdr = *ext_hdr_p;
+ int i;
+ int err;
+
+ for (i = 0; i < count; i++) {
+ const struct extension_type *type;
+ u32 len, rounded_len;
+ u16 type_code;
+
+ if (end - (const void *)ext_hdr < sizeof(*ext_hdr)) {
+ pr_warn("Extension list overflows buffer\n");
+ return -EINVAL;
+ }
+ type_code = le16_to_cpu(ext_hdr->type);
+ if (type_code >= ARRAY_SIZE(extension_types) ||
+ !extension_types[type_code].parse) {
+ pr_warn("Unknown extension type: %u\n", type_code);
+ return -EINVAL;
+ }
+ type = &extension_types[type_code];
+ if (authenticated != !type->unauthenticated) {
+ pr_warn("Extension type %u must be %sauthenticated\n",
+ type_code, type->unauthenticated ? "un" : "");
+ return -EINVAL;
+ }
+ if (ext_hdr->reserved) {
+ pr_warn("Reserved bits set in extension header\n");
+ return -EINVAL;
+ }
+ len = le32_to_cpu(ext_hdr->length);
+ if (len < sizeof(*ext_hdr)) {
+ pr_warn("Invalid length in extension header\n");
+ return -EINVAL;
+ }
+ rounded_len = round_up(len, 8);
+ if (rounded_len == 0 ||
+ rounded_len > end - (const void *)ext_hdr) {
+ pr_warn("Extension item overflows buffer\n");
+ return -EINVAL;
+ }
+ if (len < sizeof(*ext_hdr) + type->base_len) {
+ pr_warn("Extension length too small for type\n");
+ return -EINVAL;
+ }
+ err = type->parse(vi, ext_hdr + 1,
+ len - sizeof(*ext_hdr) - type->base_len);
+ if (err)
+ return err;
+ ext_hdr = (const void *)ext_hdr + rounded_len;
+ }
+ *ext_hdr_p = ext_hdr;
+ return 0;
+}
+
+/*
+ * Parse the extension items following the fixed-size portion of the fs-verity
+ * descriptor. The fsverity_info is updated accordingly.
+ *
+ * Return: On success, the size of the authenticated portion of the descriptor
+ * (the fixed-size portion plus the authenticated extensions).
+ * Otherwise, a -errno value.
+ */
+static int parse_extensions(struct fsverity_info *vi,
+ const struct fsverity_descriptor *desc,
+ int desc_len)
+{
+ const struct fsverity_extension *ext_hdr = (const void *)(desc + 1);
+ const void *end = (const void *)desc + desc_len;
+ u16 auth_ext_count = le16_to_cpu(desc->auth_ext_count);
+ int auth_desc_len;
+ int err;
+
+ /* Authenticated extensions */
+ err = do_parse_extensions(vi, &ext_hdr, end, auth_ext_count, true);
+ if (err)
+ return err;
+ auth_desc_len = (void *)ext_hdr - (void *)desc;
+
+ /*
+ * Unauthenticated extensions (optional). Careful: an attacker able to
+ * corrupt the file can change these arbitrarily without being detected.
+ * Thus, only specific types of extensions are whitelisted here --
+ * namely, the ones containing a signature of the file measurement,
+ * which by definition can't be included in the file measurement itself.
+ */
+ if (end - (void *)ext_hdr >= 8) {
+ u16 unauth_ext_count = le16_to_cpup((__le16 *)ext_hdr);
+
+ ext_hdr = (void *)ext_hdr + 8;
+ err = do_parse_extensions(vi, &ext_hdr, end,
+ unauth_ext_count, false);
+ if (err)
+ return err;
+ }
+
+ return auth_desc_len;
+}
+
+/*
+ * Parse an fs-verity descriptor, loading information into the fsverity_info.
+ *
+ * Return: On success, the size of the authenticated portion of the descriptor
+ * (the fixed-size portion plus the authenticated extensions).
+ * Otherwise, a -errno value.
+ */
+static int parse_fsverity_descriptor(struct fsverity_info *vi,
+ const struct fsverity_descriptor *desc,
+ int desc_len)
+{
+ unsigned int alg_num;
+ unsigned int hashes_per_block;
+ int desc_auth_len;
+ int err;
+
+ BUILD_BUG_ON(sizeof(*desc) != 64);
+
+ /* magic */
+ if (memcmp(desc->magic, FS_VERITY_MAGIC, sizeof(desc->magic))) {
+ pr_warn("Wrong magic bytes\n");
+ return -EINVAL;
+ }
+
+ /* major_version */
+ if (desc->major_version != 1) {
+ pr_warn("Unsupported major version (%u)\n",
+ desc->major_version);
+ return -EINVAL;
+ }
+
+ /* minor_version */
+ if (desc->minor_version != 0) {
+ pr_warn("Unsupported minor version (%u)\n",
+ desc->minor_version);
+ return -EINVAL;
+ }
+
+ /* data_algorithm and tree_algorithm */
+ alg_num = le16_to_cpu(desc->data_algorithm);
+ if (alg_num != le16_to_cpu(desc->tree_algorithm)) {
+ pr_warn("Unimplemented case: data (%u) and tree (%u) hash algorithms differ\n",
+ alg_num, le16_to_cpu(desc->tree_algorithm));
+ return -EINVAL;
+ }
+ vi->hash_alg = fsverity_get_hash_alg(alg_num);
+ if (IS_ERR(vi->hash_alg))
+ return PTR_ERR(vi->hash_alg);
+
+ /* log_data_blocksize and log_tree_blocksize */
+ if (desc->log_data_blocksize != PAGE_SHIFT) {
+ pr_warn("Unsupported log_blocksize (%u). Need block_size == PAGE_SIZE.\n",
+ desc->log_data_blocksize);
+ return -EINVAL;
+ }
+ if (desc->log_tree_blocksize != desc->log_data_blocksize) {
+ pr_warn("Unimplemented case: data (%u) and tree (%u) block sizes differ\n",
+ desc->log_data_blocksize, desc->log_data_blocksize);
+ return -EINVAL;
+ }
+ vi->block_bits = desc->log_data_blocksize;
+ hashes_per_block = (1 << vi->block_bits) / vi->hash_alg->digest_size;
+ if (!is_power_of_2(hashes_per_block)) {
+ pr_warn("Unimplemented case: hashes per block (%u) isn't a power of 2\n",
+ hashes_per_block);
+ return -EINVAL;
+ }
+ vi->log_arity = ilog2(hashes_per_block);
+
+ /* flags */
+ if (desc->flags) {
+ pr_warn("Unsupported flags (%#x)\n", le32_to_cpu(desc->flags));
+ return -EINVAL;
+ }
+
+ /* reserved fields */
+ if (desc->reserved1 ||
+ memchr_inv(desc->reserved2, 0, sizeof(desc->reserved2))) {
+ pr_warn("Reserved bits set in fsverity_descriptor\n");
+ return -EINVAL;
+ }
+
+ /* orig_file_size */
+ vi->data_i_size = le64_to_cpu(desc->orig_file_size);
+ if (vi->data_i_size <= 0) {
+ pr_warn("Original file size is 0 or negative; this is unsupported\n");
+ return -EINVAL;
+ }
+
+ /* extensions */
+ desc_auth_len = parse_extensions(vi, desc, desc_len);
+ if (desc_auth_len < 0)
+ return desc_auth_len;
+
+ if (!vi->have_root_hash) {
+ pr_warn("Root hash wasn't found!\n");
+ return -EINVAL;
+ }
+
+ /* Use an empty salt if no salt was found in the extensions list */
+ if (!vi->hashstate) {
+ err = set_salt(vi, "", 0);
+ if (err)
+ return err;
+ }
+
+ return desc_auth_len;
+}
+
+/*
+ * Calculate the depth of the Merkle tree, then create a map from level to the
+ * block offset at which that level's hash blocks start. Level 'depth - 1' is
+ * the root and is stored first. Level 0 is the level directly "above" the data
+ * blocks and is stored last, just before the fsverity_descriptor.
+ */
+static int compute_tree_depth_and_offsets(struct fsverity_info *vi)
+{
+ unsigned int hashes_per_block = 1 << vi->log_arity;
+ u64 blocks = ((u64)vi->data_i_size + (1 << vi->block_bits) - 1) >>
+ vi->block_bits;
+ u64 offset = blocks; /* assuming Merkle tree past EOF */
+ int depth = 0;
+ int i;
+
+ while (blocks > 1) {
+ if (depth >= FS_VERITY_MAX_LEVELS) {
+ pr_warn("Too many tree levels (max is %d)\n",
+ FS_VERITY_MAX_LEVELS);
+ return -EINVAL;
+ }
+ blocks = (blocks + hashes_per_block - 1) >> vi->log_arity;
+ vi->hash_lvl_region_idx[depth++] = blocks;
+ }
+ vi->depth = depth;
+
+ for (i = depth - 1; i >= 0; i--) {
+ u64 next_count = vi->hash_lvl_region_idx[i];
+
+ vi->hash_lvl_region_idx[i] = offset;
+ pr_debug("Level %d is [%llu..%llu] (%llu blocks)\n",
+ i, offset, offset + next_count - 1, next_count);
+ offset += next_count;
+ }
+ return 0;
+}
+
+/* Arbitrary limit, can be increased if needed */
+#define MAX_DESCRIPTOR_PAGES 16
+
+/*
+ * Compute the file's measurement by hashing the first 'desc_auth_len' bytes of
+ * the fs-verity descriptor (which includes the Merkle tree root hash as an
+ * authenticated extension item).
+ *
+ * Note: 'desc' may point into vmap'ed memory, so it can't be passed directly to
+ * sg_set_buf() for the ahash API. Instead, we pass the pages directly.
+ */
+static int compute_measurement(const struct fsverity_info *vi,
+ const struct fsverity_descriptor *desc,
+ int desc_auth_len,
+ struct page *desc_pages[MAX_DESCRIPTOR_PAGES],
+ int nr_desc_pages, u8 *measurement)
+{
+ struct ahash_request *req;
+ DECLARE_CRYPTO_WAIT(wait);
+ struct scatterlist sg[MAX_DESCRIPTOR_PAGES];
+ int offset, len, remaining;
+ int i;
+ int err;
+
+ req = ahash_request_alloc(vi->hash_alg->tfm, GFP_KERNEL);
+ if (!req)
+ return -ENOMEM;
+
+ sg_init_table(sg, nr_desc_pages);
+ offset = offset_in_page(desc);
+ remaining = desc_auth_len;
+ for (i = 0; i < nr_desc_pages && remaining; i++) {
+ len = min_t(int, PAGE_SIZE - offset, remaining);
+ sg_set_page(&sg[i], desc_pages[i], len, offset);
+ remaining -= len;
+ offset = 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, measurement, desc_auth_len);
+ err = crypto_wait_req(crypto_ahash_digest(req), &wait);
+ ahash_request_free(req);
+ return err;
+}
+
+static struct fsverity_info *alloc_fsverity_info(void)
+{
+ return kmem_cache_zalloc(fsverity_info_cachep, GFP_NOFS);
+}
+
+void free_fsverity_info(struct fsverity_info *vi)
+{
+ if (!vi)
+ return;
+ kfree(vi->hashstate);
+ kmem_cache_free(fsverity_info_cachep, vi);
+}
+
+/**
+ * find_fsverity_footer - find the fsverity_footer in the last page of metadata
+ *
+ * Allow the fs-verity footer to be padded with zeroes. This is needed by ext4,
+ * which stores the fs-verity metadata beyond EOF but sets i_size = data_i_size.
+ * Then, the fs-verity footer must be found implicitly via the last extent.
+ *
+ * Return: pointer to the footer if found, else NULL
+ */
+static const struct fsverity_footer *
+find_fsverity_footer(const u8 *last_virt, size_t last_validsize)
+{
+ const u8 *p = last_virt + last_validsize;
+ const struct fsverity_footer *ftr;
+
+ /* Find the last nonzero byte, which should be ftr->magic[7] */
+ do {
+ if (p <= last_virt)
+ return NULL;
+ } while (*--p == 0);
+
+ BUILD_BUG_ON(sizeof(ftr->magic) != 8);
+ BUILD_BUG_ON(offsetof(struct fsverity_footer, magic[8]) !=
+ sizeof(*ftr));
+ if (p - last_virt < offsetof(struct fsverity_footer, magic[7]))
+ return NULL;
+ ftr = container_of(p, struct fsverity_footer, magic[7]);
+ if (memcmp(ftr->magic, FS_VERITY_MAGIC, sizeof(ftr->magic)))
+ return NULL;
+ return ftr;
+}
+
+struct page *fsverity_read_metadata_page(struct inode *inode, pgoff_t index)
+{
+ /*
+ * For now we assume that the verity metadata is stored in the same data
+ * stream as the actual file contents (as ext4 and f2fs do), so we read
+ * the metadata directly from the inode's page cache. If any
+ * filesystems need to do things differently, this should be replaced
+ * with a method fsverity_operations.read_metadata_page().
+ */
+ return read_mapping_page(inode->i_mapping, index, NULL);
+}
+
+/**
+ * map_fsverity_descriptor - map an inode's fs-verity descriptor into memory
+ *
+ * If the descriptor fits in one page, we use kmap; otherwise we use vmap.
+ * unmap_fsverity_descriptor() must be called later to unmap it.
+ *
+ * It's assumed that the file contents cannot be modified concurrently.
+ * (This is guaranteed by either deny_write_access() or by the verity bit.)
+ *
+ * Return: the virtual address of the start of the descriptor, in virtually
+ * contiguous memory. Also fills in desc_pages and returns in *desc_len the
+ * length of the descriptor including all extensions, and in *desc_start the
+ * offset of the descriptor from the start of the file, in bytes.
+ */
+static const struct fsverity_descriptor *
+map_fsverity_descriptor(struct inode *inode, loff_t metadata_end,
+ struct page *desc_pages[MAX_DESCRIPTOR_PAGES],
+ int *nr_desc_pages, int *desc_len, loff_t *desc_start)
+{
+ const int last_validsize = ((metadata_end - 1) & ~PAGE_MASK) + 1;
+ const pgoff_t last_pgoff = (metadata_end - 1) >> PAGE_SHIFT;
+ struct page *last_page;
+ const void *last_virt;
+ const struct fsverity_footer *ftr;
+ pgoff_t first_pgoff;
+ u32 desc_reverse_offset;
+ pgoff_t pgoff;
+ const void *desc_virt;
+ int i;
+ int err;
+
+ *nr_desc_pages = 0;
+ *desc_len = 0;
+ *desc_start = 0;
+
+ last_page = fsverity_read_metadata_page(inode, last_pgoff);
+ if (IS_ERR(last_page)) {
+ pr_warn("Error reading last page: %ld\n", PTR_ERR(last_page));
+ return ERR_CAST(last_page);
+ }
+ last_virt = kmap(last_page);
+
+ ftr = find_fsverity_footer(last_virt, last_validsize);
+ if (!ftr) {
+ pr_warn("No verity metadata found\n");
+ err = -EINVAL;
+ goto err_out;
+ }
+ metadata_end -= (last_virt + last_validsize - sizeof(*ftr)) -
+ (void *)ftr;
+
+ desc_reverse_offset = le32_to_cpu(ftr->desc_reverse_offset);
+ if (desc_reverse_offset <
+ sizeof(struct fsverity_descriptor) + sizeof(*ftr) ||
+ desc_reverse_offset > metadata_end) {
+ pr_warn("Unexpected desc_reverse_offset: %u\n",
+ desc_reverse_offset);
+ err = -EINVAL;
+ goto err_out;
+ }
+ *desc_start = metadata_end - desc_reverse_offset;
+ if (*desc_start & 7) {
+ pr_warn("fs-verity descriptor is misaligned (desc_start=%lld)\n",
+ *desc_start);
+ err = -EINVAL;
+ goto err_out;
+ }
+
+ first_pgoff = *desc_start >> PAGE_SHIFT;
+ if (last_pgoff - first_pgoff >= MAX_DESCRIPTOR_PAGES) {
+ pr_warn("fs-verity descriptor is too long (%lu pages)\n",
+ last_pgoff - first_pgoff + 1);
+ err = -EINVAL;
+ goto err_out;
+ }
+
+ *desc_len = desc_reverse_offset - sizeof(__le32);
+
+ if (first_pgoff == last_pgoff) {
+ /* Single-page descriptor; use the already-kmapped last page */
+ desc_pages[0] = last_page;
+ *nr_desc_pages = 1;
+ return last_virt + (*desc_start & ~PAGE_MASK);
+ }
+
+ /* Multi-page descriptor; map the additional pages into memory */
+
+ for (pgoff = first_pgoff; pgoff < last_pgoff; pgoff++) {
+ struct page *page;
+
+ page = fsverity_read_metadata_page(inode, pgoff);
+ if (IS_ERR(page)) {
+ err = PTR_ERR(page);
+ pr_warn("Error reading descriptor page: %d\n", err);
+ goto err_out;
+ }
+ desc_pages[(*nr_desc_pages)++] = page;
+ }
+
+ desc_pages[(*nr_desc_pages)++] = last_page;
+ kunmap(last_page);
+ last_page = NULL;
+
+ desc_virt = vmap(desc_pages, *nr_desc_pages, VM_MAP, PAGE_KERNEL_RO);
+ if (!desc_virt) {
+ err = -ENOMEM;
+ goto err_out;
+ }
+
+ return desc_virt + (*desc_start & ~PAGE_MASK);
+
+err_out:
+ for (i = 0; i < *nr_desc_pages; i++)
+ put_page(desc_pages[i]);
+ if (last_page) {
+ kunmap(last_page);
+ put_page(last_page);
+ }
+ return ERR_PTR(err);
+}
+
+static void
+unmap_fsverity_descriptor(const struct fsverity_descriptor *desc,
+ struct page *desc_pages[MAX_DESCRIPTOR_PAGES],
+ int nr_desc_pages)
+{
+ int i;
+
+ if (is_vmalloc_addr(desc)) {
+ vunmap((void *)((unsigned long)desc & PAGE_MASK));
+ } else {
+ WARN_ON(nr_desc_pages != 1);
+ kunmap(desc_pages[0]);
+ }
+ for (i = 0; i < nr_desc_pages; i++)
+ put_page(desc_pages[i]);
+}
+
+/* Read the file's fs-verity descriptor and create an fsverity_info for it */
+struct fsverity_info *create_fsverity_info(struct inode *inode, bool enabling)
+{
+ struct fsverity_info *vi;
+ const struct fsverity_descriptor *desc = NULL;
+ struct page *desc_pages[MAX_DESCRIPTOR_PAGES];
+ int nr_desc_pages;
+ int desc_len;
+ loff_t desc_start;
+ int desc_auth_len;
+ int err;
+
+ vi = alloc_fsverity_info();
+ if (!vi)
+ return ERR_PTR(-ENOMEM);
+
+ if (enabling) {
+ /* file is in fsveritysetup format */
+ vi->metadata_end = i_size_read(inode);
+ } else {
+ /* verity metadata may be in a filesystem-specific location */
+ err = inode->i_sb->s_vop->get_metadata_end(inode,
+ &vi->metadata_end);
+ if (err)
+ goto out;
+ }
+
+ desc = map_fsverity_descriptor(inode, vi->metadata_end, desc_pages,
+ &nr_desc_pages, &desc_len, &desc_start);
+ if (IS_ERR(desc)) {
+ err = PTR_ERR(desc);
+ desc = NULL;
+ goto out;
+ }
+
+ dump_fsverity_descriptor(desc);
+ desc_auth_len = parse_fsverity_descriptor(vi, desc, desc_len);
+ if (desc_auth_len < 0) {
+ err = desc_auth_len;
+ goto out;
+ }
+ if (vi->data_i_size > i_size_read(inode)) {
+ pr_warn("Bad data_i_size: %llu\n", vi->data_i_size);
+ err = -EINVAL;
+ goto out;
+ }
+
+ err = compute_tree_depth_and_offsets(vi);
+ if (err)
+ goto out;
+ err = compute_measurement(vi, desc, desc_auth_len, desc_pages,
+ nr_desc_pages, vi->measurement);
+out:
+ if (desc)
+ unmap_fsverity_descriptor(desc, desc_pages, nr_desc_pages);
+ if (err) {
+ free_fsverity_info(vi);
+ vi = ERR_PTR(err);
+ }
+ return vi;
+}
+
+/* Ensure the inode has an ->i_verity_info */
+static int setup_fsverity_info(struct inode *inode)
+{
+ struct fsverity_info *vi = get_fsverity_info(inode);
+
+ if (vi)
+ return 0;
+
+ vi = create_fsverity_info(inode, false);
+ if (IS_ERR(vi))
+ return PTR_ERR(vi);
+
+ if (!set_fsverity_info(inode, vi))
+ free_fsverity_info(vi);
+ return 0;
+}
+
+/**
+ * fsverity_file_open - prepare to open a verity file
+ * @inode: the inode being opened
+ * @filp: the struct file being set up
+ *
+ * When opening a verity file, deny the open if it is for writing. Otherwise,
+ * set up the inode's ->i_verity_info (if not already done) by parsing the
+ * verity metadata at the end of the file.
+ *
+ * When combined with fscrypt, this must be called after fscrypt_file_open().
+ * Otherwise, we won't have the key set up to decrypt the verity metadata.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fsverity_file_open(struct inode *inode, struct file *filp)
+{
+ if (filp->f_mode & FMODE_WRITE) {
+ pr_debug("Denying opening verity file (ino %lu) for write\n",
+ inode->i_ino);
+ return -EPERM;
+ }
+
+ return setup_fsverity_info(inode);
+}
+EXPORT_SYMBOL_GPL(fsverity_file_open);
+
+/**
+ * fsverity_prepare_setattr - prepare to change a verity inode's attributes
+ * @dentry: dentry through which the inode is being changed
+ * @attr: attributes to change
+ *
+ * Verity files are immutable, so deny truncates. This isn't covered by the
+ * open-time check because sys_truncate() takes a path, not a file descriptor.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr)
+{
+ if (attr->ia_valid & ATTR_SIZE) {
+ pr_debug("Denying truncate of verity file (ino %lu)\n",
+ d_inode(dentry)->i_ino);
+ return -EPERM;
+ }
+ return 0;
+}
+EXPORT_SYMBOL_GPL(fsverity_prepare_setattr);
+
+/**
+ * fsverity_prepare_getattr - prepare to get a verity inode's attributes
+ * @inode: the inode for which the attributes are being retrieved
+ *
+ * This only needs to be called by filesystems that set the on-disk i_size of
+ * verity files to something other than the data size, as then this is needed to
+ * override i_size so that stat() shows the correct size.
+ *
+ * When the filesystem supports fscrypt too, it must make sure to set up the
+ * inode's encryption key (if needed) before calling this.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fsverity_prepare_getattr(struct inode *inode)
+{
+ return setup_fsverity_info(inode);
+}
+EXPORT_SYMBOL_GPL(fsverity_prepare_getattr);
+
+/**
+ * fsverity_cleanup_inode - free the inode's verity info, if present
+ *
+ * Filesystems must call this on inode eviction to free ->i_verity_info.
+ */
+void fsverity_cleanup_inode(struct inode *inode)
+{
+ free_fsverity_info(inode->i_verity_info);
+ inode->i_verity_info = NULL;
+}
+EXPORT_SYMBOL_GPL(fsverity_cleanup_inode);
+
+/**
+ * fsverity_full_i_size - get the full file size
+ *
+ * If the file has fs-verity set up, return the full file size including the
+ * verity metadata. Otherwise just return i_size. This is only meaningful when
+ * the filesystem stores the verity metadata past EOF.
+ */
+loff_t fsverity_full_i_size(const struct inode *inode)
+{
+ struct fsverity_info *vi = get_fsverity_info(inode);
+
+ if (vi)
+ return vi->metadata_end;
+
+ return i_size_read(inode);
+}
+EXPORT_SYMBOL_GPL(fsverity_full_i_size);
+
+static int __init fsverity_module_init(void)
+{
+ fsverity_info_cachep = KMEM_CACHE(fsverity_info, SLAB_RECLAIM_ACCOUNT);
+ if (!fsverity_info_cachep)
+ return -ENOMEM;
+
+ fsverity_check_hash_algs();
+
+ pr_debug("Initialized fs-verity\n");
+ return 0;
+}
+
+static void __exit fsverity_module_exit(void)
+{
+ kmem_cache_destroy(fsverity_info_cachep);
+ fsverity_exit_hash_algs();
+}
+
+module_init(fsverity_module_init)
+module_exit(fsverity_module_exit);
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("fs-verity: read-only file-based authenticity protection");
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8252df30b9a16..bcfc400627574 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -61,6 +61,8 @@ struct workqueue_struct;
struct iov_iter;
struct fscrypt_info;
struct fscrypt_operations;
+struct fsverity_info;
+struct fsverity_operations;

extern void __init inode_init(void);
extern void __init inode_init_early(void);
@@ -702,6 +704,10 @@ struct inode {
struct fscrypt_info *i_crypt_info;
#endif

+#if IS_ENABLED(CONFIG_FS_VERITY)
+ struct fsverity_info *i_verity_info;
+#endif
+
void *i_private; /* fs or device private pointer */
} __randomize_layout;

@@ -1400,6 +1406,9 @@ struct super_block {
const struct xattr_handler **s_xattr;
#if IS_ENABLED(CONFIG_FS_ENCRYPTION)
const struct fscrypt_operations *s_cop;
+#endif
+#if IS_ENABLED(CONFIG_FS_VERITY)
+ const struct fsverity_operations *s_vop;
#endif
struct hlist_bl_head s_roots; /* alternate root dentries for NFS */
struct list_head s_mounts; /* list of mounts; _not_ for fs use */
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h
new file mode 100644
index 0000000000000..c9422a579c160
--- /dev/null
+++ b/include/linux/fsverity.h
@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * fs-verity: read-only file-based authenticity protection
+ *
+ * Copyright 2018 Google LLC
+ */
+
+#ifndef _LINUX_FSVERITY_H
+#define _LINUX_FSVERITY_H
+
+#include <linux/fs.h>
+#include <uapi/linux/fsverity.h>
+
+/*
+ * fs-verity operations for filesystems
+ */
+struct fsverity_operations {
+ int (*set_verity)(struct inode *inode, loff_t data_i_size);
+ int (*get_metadata_end)(struct inode *inode, loff_t *metadata_end_ret);
+};
+
+#if __FS_HAS_VERITY
+
+/* setup.c */
+extern int fsverity_file_open(struct inode *inode, struct file *filp);
+extern int fsverity_prepare_setattr(struct dentry *dentry, struct iattr *attr);
+extern int fsverity_prepare_getattr(struct inode *inode);
+extern void fsverity_cleanup_inode(struct inode *inode);
+extern loff_t fsverity_full_i_size(const struct inode *inode);
+
+#else /* !__FS_HAS_VERITY */
+
+/* setup.c */
+
+static inline int fsverity_file_open(struct inode *inode, struct file *filp)
+{
+ return -EOPNOTSUPP;
+}
+
+static inline int fsverity_prepare_setattr(struct dentry *dentry,
+ struct iattr *attr)
+{
+ return -EOPNOTSUPP;
+}
+
+static inline int fsverity_prepare_getattr(struct inode *inode)
+{
+ return -EOPNOTSUPP;
+}
+
+static inline void fsverity_cleanup_inode(struct inode *inode)
+{
+}
+
+static inline loff_t fsverity_full_i_size(const struct inode *inode)
+{
+ return i_size_read(inode);
+}
+
+#endif /* !__FS_HAS_VERITY */
+
+#endif /* _LINUX_FSVERITY_H */
diff --git a/include/uapi/linux/fsverity.h b/include/uapi/linux/fsverity.h
new file mode 100644
index 0000000000000..55b9f32676220
--- /dev/null
+++ b/include/uapi/linux/fsverity.h
@@ -0,0 +1,86 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * fs-verity (file-based verity) support
+ *
+ * Copyright (C) 2018 Google LLC
+ */
+#ifndef _UAPI_LINUX_FSVERITY_H
+#define _UAPI_LINUX_FSVERITY_H
+
+#include <linux/limits.h>
+#include <linux/ioctl.h>
+#include <linux/types.h>
+
+/* ========== Ioctls ========== */
+
+struct fsverity_digest {
+ __u16 digest_algorithm;
+ __u16 digest_size; /* input/output */
+ __u8 digest[];
+};
+
+#define FS_IOC_ENABLE_VERITY _IO('f', 133)
+#define FS_IOC_MEASURE_VERITY _IOWR('f', 134, struct fsverity_digest)
+
+/* ========== On-disk format ========== */
+
+#define FS_VERITY_MAGIC "FSVerity"
+
+/* Supported hash algorithms */
+#define FS_VERITY_ALG_SHA256 1
+
+/* Metadata stored near the end of verity files, after the Merkle tree */
+/* This structure is 64 bytes long */
+struct fsverity_descriptor {
+ __u8 magic[8]; /* must be FS_VERITY_MAGIC */
+ __u8 major_version; /* must be 1 */
+ __u8 minor_version; /* must be 0 */
+ __u8 log_data_blocksize;/* log2(data-bytes-per-hash), e.g. 12 for 4KB */
+ __u8 log_tree_blocksize;/* log2(tree-bytes-per-hash), e.g. 12 for 4KB */
+ __le16 data_algorithm; /* hash algorithm for data blocks */
+ __le16 tree_algorithm; /* hash algorithm for tree blocks */
+ __le32 flags; /* flags */
+ __le32 reserved1; /* must be 0 */
+ __le64 orig_file_size; /* size of the original file data */
+ __le16 auth_ext_count; /* number of authenticated extensions */
+ __u8 reserved2[30]; /* must be 0 */
+};
+/* followed by list of 'auth_ext_count' authenticated extensions */
+/*
+ * then followed by '__le16 unauth_ext_count' padded to next 8-byte boundary,
+ * then a list of 'unauth_ext_count' (may be 0) unauthenticated extensions
+ */
+
+/* Extension types */
+#define FS_VERITY_EXT_ROOT_HASH 1
+#define FS_VERITY_EXT_SALT 2
+
+/* Header of each extension (variable-length metadata item) */
+struct fsverity_extension {
+ /*
+ * Length in bytes, including this header but excluding padding to next
+ * 8-byte boundary that is applied when advancing to the next extension.
+ */
+ __le32 length;
+ __le16 type; /* Type of this extension (see codes above) */
+ __le16 reserved; /* Reserved, must be 0 */
+};
+/* followed by the payload of 'length - 8' bytes */
+
+/* Extension payload formats */
+
+/*
+ * FS_VERITY_EXT_ROOT_HASH payload is just a byte array, with size equal to the
+ * digest size of the hash algorithm given in the fsverity_descriptor
+ */
+
+/* FS_VERITY_EXT_SALT payload is just a byte array, any size */
+
+
+/* Fields stored at the very end of the file */
+struct fsverity_footer {
+ __le32 desc_reverse_offset; /* distance to fsverity_descriptor */
+ __u8 magic[8]; /* FS_VERITY_MAGIC */
+} __packed;
+
+#endif /* _UAPI_LINUX_FSVERITY_H */
--
2.19.1.568.g152ad8e336-goog