1/* SPDX-License-Identifier: GPL-2.0 */
2/*
3 * fs-verity: read-only file-based authenticity protection
4 *
5 * Copyright 2019 Google LLC
6 */
7
8#ifndef _FSVERITY_PRIVATE_H
9#define _FSVERITY_PRIVATE_H
10
11#ifdef CONFIG_FS_VERITY_DEBUG
12#define DEBUG
13#endif
14
15#define pr_fmt(fmt) "fs-verity: " fmt
16
17#include <crypto/sha.h>
18#include <linux/fsverity.h>
19#include <linux/mempool.h>
20#include <linux/code_sign.h>
21
22struct ahash_request;
23
24/*
25 * Implementation limit: maximum depth of the Merkle tree.  For now 8 is plenty;
26 * it's enough for over U64_MAX bytes of data using SHA-256 and 4K blocks.
27 */
28#define FS_VERITY_MAX_LEVELS		8
29
30/*
31 * Largest digest size among all hash algorithms supported by fs-verity.
32 * Currently assumed to be <= size of fsverity_descriptor::root_hash.
33 */
34#define FS_VERITY_MAX_DIGEST_SIZE	SHA512_DIGEST_SIZE
35
36/* A hash algorithm supported by fs-verity */
37struct fsverity_hash_alg {
38	struct crypto_ahash *tfm; /* hash tfm, allocated on demand */
39	const char *name;	  /* crypto API name, e.g. sha256 */
40	unsigned int digest_size; /* digest size in bytes, e.g. 32 for SHA-256 */
41	unsigned int block_size;  /* block size in bytes, e.g. 64 for SHA-256 */
42	mempool_t req_pool;	  /* mempool with a preallocated hash request */
43};
44
45/* Merkle tree parameters: hash algorithm, initial hash state, and topology */
46struct merkle_tree_params {
47	struct fsverity_hash_alg *hash_alg; /* the hash algorithm */
48	const u8 *hashstate;		/* initial hash state or NULL */
49	unsigned int digest_size;	/* same as hash_alg->digest_size */
50	unsigned int block_size;	/* size of data and tree blocks */
51	unsigned int hashes_per_block;	/* number of hashes per tree block */
52	unsigned int log_blocksize;	/* log2(block_size) */
53	unsigned int log_arity;		/* log2(hashes_per_block) */
54	unsigned int num_levels;	/* number of levels in Merkle tree */
55	u64 tree_size;			/* Merkle tree size in bytes */
56	unsigned long level0_blocks;	/* number of blocks in tree level 0 */
57
58	/*
59	 * Starting block index for each tree level, ordered from leaf level (0)
60	 * to root level ('num_levels - 1')
61	 */
62	u64 level_start[FS_VERITY_MAX_LEVELS];
63};
64
65/*
66 * fsverity_info - cached verity metadata for an inode
67 *
68 * When a verity file is first opened, an instance of this struct is allocated
69 * and stored in ->i_verity_info; it remains until the inode is evicted.  It
70 * caches information about the Merkle tree that's needed to efficiently verify
71 * data read from the file.  It also caches the file measurement.  The Merkle
72 * tree pages themselves are not cached here, but the filesystem may cache them.
73 */
74struct fsverity_info {
75	struct merkle_tree_params tree_params;
76	u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE];
77	u8 measurement[FS_VERITY_MAX_DIGEST_SIZE];
78	const struct inode *inode;
79#ifdef CONFIG_SECURITY_CODE_SIGN
80	struct cs_info fcs_info;
81	u64 verified_data_size;
82	int cert_type;
83#endif
84};
85
86/*
87 * Merkle tree properties.  The file measurement is the hash of this structure
88 * excluding the signature and with the sig_size field set to 0.
89 */
90struct fsverity_descriptor {
91	__u8 version;		/* must be 1 */
92	__u8 hash_algorithm;	/* Merkle tree hash algorithm */
93	__u8 log_blocksize;	/* log2 of size of data and tree blocks */
94	__u8 salt_size;		/* size of salt in bytes; 0 if none */
95	__le32 sig_size;	/* size of signature in bytes; 0 if none */
96	__le64 data_size;	/* size of file the Merkle tree is built over */
97	__u8 root_hash[64];	/* Merkle tree root hash */
98	__u8 salt[32];		/* salt prepended to each hashed block */
99	__u8 __reserved[144];	/* must be 0's */
100	__u8 signature[];	/* optional PKCS#7 signature */
101};
102
103/* Arbitrary limit to bound the kmalloc() size.  Can be changed. */
104#define FS_VERITY_MAX_DESCRIPTOR_SIZE	16384
105
106#define FS_VERITY_MAX_SIGNATURE_SIZE	(FS_VERITY_MAX_DESCRIPTOR_SIZE - \
107					 sizeof(struct fsverity_descriptor))
108
109/*
110 * Format in which verity file measurements are signed.  This is the same as
111 * 'struct fsverity_digest', except here some magic bytes are prepended to
112 * provide some context about what is being signed in case the same key is used
113 * for non-fsverity purposes, and here the fields have fixed endianness.
114 */
115struct fsverity_signed_digest {
116	char magic[8];			/* must be "FSVerity" */
117	__le16 digest_algorithm;
118	__le16 digest_size;
119	__u8 digest[];
120};
121
122/* hash_algs.c */
123
124extern struct fsverity_hash_alg fsverity_hash_algs[];
125
126extern int g_fsverity_hash_algs_num;
127
128struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
129						unsigned int num);
130struct ahash_request *fsverity_alloc_hash_request(struct fsverity_hash_alg *alg,
131						  gfp_t gfp_flags);
132void fsverity_free_hash_request(struct fsverity_hash_alg *alg,
133				struct ahash_request *req);
134const u8 *fsverity_prepare_hash_state(struct fsverity_hash_alg *alg,
135				      const u8 *salt, size_t salt_size);
136int fsverity_hash_page(const struct merkle_tree_params *params,
137		       const struct inode *inode,
138		       struct ahash_request *req, struct page *page, u8 *out);
139int fsverity_hash_buffer(struct fsverity_hash_alg *alg,
140			 const void *data, size_t size, u8 *out);
141void __init fsverity_check_hash_algs(void);
142
143/* init.c */
144
145void __printf(3, 4) __cold
146fsverity_msg(const struct inode *inode, const char *level,
147	     const char *fmt, ...);
148
149#define fsverity_warn(inode, fmt, ...)		\
150	fsverity_msg((inode), KERN_WARNING, fmt, ##__VA_ARGS__)
151#define fsverity_err(inode, fmt, ...)		\
152	fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
153
154/* open.c */
155
156int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
157				     const struct inode *inode,
158				     unsigned int hash_algorithm,
159				     unsigned int log_blocksize,
160				     const u8 *salt, size_t salt_size,
161				     u64 data_size);
162
163struct fsverity_info *fsverity_create_info(const struct inode *inode,
164					   void *desc, size_t desc_size);
165
166void fsverity_set_info(struct inode *inode, struct fsverity_info *vi);
167
168void fsverity_free_info(struct fsverity_info *vi);
169
170int __init fsverity_init_info_cache(void);
171void __init fsverity_exit_info_cache(void);
172
173/* signature.c */
174
175#ifdef CONFIG_FS_VERITY_BUILTIN_SIGNATURES
176int fsverity_verify_signature(struct fsverity_info *vi,
177			      const struct fsverity_descriptor *desc,
178			      size_t desc_size);
179
180int __init fsverity_init_signature(void);
181#else /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */
182static inline int
183fsverity_verify_signature(struct fsverity_info *vi,
184			  const struct fsverity_descriptor *desc,
185			  size_t desc_size)
186{
187	return 0;
188}
189
190static inline int fsverity_init_signature(void)
191{
192	return 0;
193}
194#endif /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */
195
196/* verify.c */
197
198int __init fsverity_init_workqueue(void);
199void __init fsverity_exit_workqueue(void);
200
201#endif /* _FSVERITY_PRIVATE_H */
202