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 #define pr_fmt(fmt) "fs-verity: " fmt
12 
13 #include <linux/fsverity.h>
14 
15 /*
16  * Implementation limit: maximum depth of the Merkle tree.  For now 8 is plenty;
17  * it's enough for over U64_MAX bytes of data using SHA-256 and 4K blocks.
18  */
19 #define FS_VERITY_MAX_LEVELS		8
20 
21 /* A hash algorithm supported by fs-verity */
22 struct fsverity_hash_alg {
23 	struct crypto_shash *tfm; /* hash tfm, allocated on demand */
24 	const char *name;	  /* crypto API name, e.g. sha256 */
25 	unsigned int digest_size; /* digest size in bytes, e.g. 32 for SHA-256 */
26 	unsigned int block_size;  /* block size in bytes, e.g. 64 for SHA-256 */
27 	/*
28 	 * The HASH_ALGO_* constant for this algorithm.  This is different from
29 	 * FS_VERITY_HASH_ALG_*, which uses a different numbering scheme.
30 	 */
31 	enum hash_algo algo_id;
32 };
33 
34 /* Merkle tree parameters: hash algorithm, initial hash state, and topology */
35 struct merkle_tree_params {
36 	const struct fsverity_hash_alg *hash_alg; /* the hash algorithm */
37 	const u8 *hashstate;		/* initial hash state or NULL */
38 	unsigned int digest_size;	/* same as hash_alg->digest_size */
39 	unsigned int block_size;	/* size of data and tree blocks */
40 	unsigned int hashes_per_block;	/* number of hashes per tree block */
41 	unsigned int blocks_per_page;	/* PAGE_SIZE / block_size */
42 	u8 log_digestsize;		/* log2(digest_size) */
43 	u8 log_blocksize;		/* log2(block_size) */
44 	u8 log_arity;			/* log2(hashes_per_block) */
45 	u8 log_blocks_per_page;		/* log2(blocks_per_page) */
46 	unsigned int num_levels;	/* number of levels in Merkle tree */
47 	u64 tree_size;			/* Merkle tree size in bytes */
48 	unsigned long tree_pages;	/* Merkle tree size in pages */
49 
50 	/*
51 	 * Starting block index for each tree level, ordered from leaf level (0)
52 	 * to root level ('num_levels - 1')
53 	 */
54 	unsigned long level_start[FS_VERITY_MAX_LEVELS];
55 };
56 
57 /*
58  * fsverity_info - cached verity metadata for an inode
59  *
60  * When a verity file is first opened, an instance of this struct is allocated
61  * and stored in ->i_verity_info; it remains until the inode is evicted.  It
62  * caches information about the Merkle tree that's needed to efficiently verify
63  * data read from the file.  It also caches the file digest.  The Merkle tree
64  * pages themselves are not cached here, but the filesystem may cache them.
65  */
66 struct fsverity_info {
67 	struct merkle_tree_params tree_params;
68 	u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE];
69 	u8 file_digest[FS_VERITY_MAX_DIGEST_SIZE];
70 	const struct inode *inode;
71 	unsigned long *hash_block_verified;
72 	spinlock_t hash_page_init_lock;
73 };
74 
75 #define FS_VERITY_MAX_SIGNATURE_SIZE	(FS_VERITY_MAX_DESCRIPTOR_SIZE - \
76 					 sizeof(struct fsverity_descriptor))
77 
78 /* hash_algs.c */
79 
80 extern struct fsverity_hash_alg fsverity_hash_algs[];
81 
82 const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
83 						      unsigned int num);
84 const u8 *fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
85 				      const u8 *salt, size_t salt_size);
86 int fsverity_hash_block(const struct merkle_tree_params *params,
87 			const struct inode *inode, const void *data, u8 *out);
88 int fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
89 			 const void *data, size_t size, u8 *out);
90 void __init fsverity_check_hash_algs(void);
91 
92 /* init.c */
93 
94 void __printf(3, 4) __cold
95 fsverity_msg(const struct inode *inode, const char *level,
96 	     const char *fmt, ...);
97 
98 #define fsverity_warn(inode, fmt, ...)		\
99 	fsverity_msg((inode), KERN_WARNING, fmt, ##__VA_ARGS__)
100 #define fsverity_err(inode, fmt, ...)		\
101 	fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
102 
103 /* open.c */
104 
105 int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
106 				     const struct inode *inode,
107 				     unsigned int hash_algorithm,
108 				     unsigned int log_blocksize,
109 				     const u8 *salt, size_t salt_size);
110 
111 struct fsverity_info *fsverity_create_info(const struct inode *inode,
112 					   struct fsverity_descriptor *desc);
113 
114 void fsverity_set_info(struct inode *inode, struct fsverity_info *vi);
115 
116 void fsverity_free_info(struct fsverity_info *vi);
117 
118 int fsverity_get_descriptor(struct inode *inode,
119 			    struct fsverity_descriptor **desc_ret);
120 
121 void __init fsverity_init_info_cache(void);
122 
123 /* signature.c */
124 
125 #ifdef CONFIG_FS_VERITY_BUILTIN_SIGNATURES
126 extern int fsverity_require_signatures;
127 int fsverity_verify_signature(const struct fsverity_info *vi,
128 			      const u8 *signature, size_t sig_size);
129 
130 void __init fsverity_init_signature(void);
131 #else /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */
132 static inline int
fsverity_verify_signature(const struct fsverity_info * vi,const u8 * signature,size_t sig_size)133 fsverity_verify_signature(const struct fsverity_info *vi,
134 			  const u8 *signature, size_t sig_size)
135 {
136 	return 0;
137 }
138 
fsverity_init_signature(void)139 static inline void fsverity_init_signature(void)
140 {
141 }
142 #endif /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */
143 
144 /* verify.c */
145 
146 void __init fsverity_init_workqueue(void);
147 
148 #endif /* _FSVERITY_PRIVATE_H */
149