fsverity_private.h

  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 */
 22struct fsverity_hash_alg {
 23	const char *name;	  /* crypto API name, e.g. sha256 */
 24	unsigned int digest_size; /* digest size in bytes, e.g. 32 for SHA-256 */
 25	unsigned int block_size;  /* block size in bytes, e.g. 64 for SHA-256 */
 26	/*
 27	 * The HASH_ALGO_* constant for this algorithm.  This is different from
 28	 * FS_VERITY_HASH_ALG_*, which uses a different numbering scheme.
 29	 */
 30	enum hash_algo algo_id;
 31};
 32
 33union fsverity_hash_ctx {
 34	struct sha256_ctx sha256;
 35	struct sha512_ctx sha512;
 36};
 37
 38/* Merkle tree parameters: hash algorithm, initial hash state, and topology */
 39struct merkle_tree_params {
 40	const struct fsverity_hash_alg *hash_alg; /* the hash algorithm */
 41	/* initial hash state if salted, NULL if unsalted */
 42	const union fsverity_hash_ctx *hashstate;
 43	unsigned int digest_size;	/* same as hash_alg->digest_size */
 44	unsigned int block_size;	/* size of data and tree blocks */
 45	unsigned int hashes_per_block;	/* number of hashes per tree block */
 46	unsigned int blocks_per_page;	/* PAGE_SIZE / block_size */
 47	u8 log_digestsize;		/* log2(digest_size) */
 48	u8 log_blocksize;		/* log2(block_size) */
 49	u8 log_arity;			/* log2(hashes_per_block) */
 50	u8 log_blocks_per_page;		/* log2(blocks_per_page) */
 51	unsigned int num_levels;	/* number of levels in Merkle tree */
 52	u64 tree_size;			/* Merkle tree size in bytes */
 53	unsigned long tree_pages;	/* Merkle tree size in pages */
 54
 55	/*
 56	 * Starting block index for each tree level, ordered from leaf level (0)
 57	 * to root level ('num_levels - 1')
 58	 */
 59	unsigned long level_start[FS_VERITY_MAX_LEVELS];
 60};
 61
 62/*
 63 * fsverity_info - cached verity metadata for an inode
 64 *
 65 * When a verity file is first opened, an instance of this struct is allocated
 66 * and a pointer to it is stored in the file's in-memory inode.  It remains
 67 * until the inode is evicted.  It caches information about the Merkle tree
 68 * that's needed to efficiently verify data read from the file.  It also caches
 69 * the file digest.  The Merkle tree pages themselves are not cached here, but
 70 * the filesystem may cache them.
 71 */
 72struct fsverity_info {
 73	struct merkle_tree_params tree_params;
 74	u8 root_hash[FS_VERITY_MAX_DIGEST_SIZE];
 75	u8 file_digest[FS_VERITY_MAX_DIGEST_SIZE];
 76	const struct inode *inode;
 77	unsigned long *hash_block_verified;
 78};
 79
 80#define FS_VERITY_MAX_SIGNATURE_SIZE	(FS_VERITY_MAX_DESCRIPTOR_SIZE - \
 81					 sizeof(struct fsverity_descriptor))
 82
 83/* hash_algs.c */
 84
 85extern const struct fsverity_hash_alg fsverity_hash_algs[];
 86
 87const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
 88						      unsigned int num);
 89union fsverity_hash_ctx *
 90fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
 91			    const u8 *salt, size_t salt_size);
 92void fsverity_hash_block(const struct merkle_tree_params *params,
 93			 const void *data, u8 *out);
 94void fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
 95			  const void *data, size_t size, u8 *out);
 96void __init fsverity_check_hash_algs(void);
 97
 98/* init.c */
 99
100void __printf(3, 4) __cold
101fsverity_msg(const struct inode *inode, const char *level,
102	     const char *fmt, ...);
103
104#define fsverity_warn(inode, fmt, ...)		\
105	fsverity_msg((inode), KERN_WARNING, fmt, ##__VA_ARGS__)
106#define fsverity_err(inode, fmt, ...)		\
107	fsverity_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
108
109/* measure.c */
110
111#ifdef CONFIG_BPF_SYSCALL
112void __init fsverity_init_bpf(void);
113#else
114static inline void fsverity_init_bpf(void)
115{
116}
117#endif
118
119/* open.c */
120
121int fsverity_init_merkle_tree_params(struct merkle_tree_params *params,
122				     const struct inode *inode,
123				     unsigned int hash_algorithm,
124				     unsigned int log_blocksize,
125				     const u8 *salt, size_t salt_size);
126
127struct fsverity_info *fsverity_create_info(const struct inode *inode,
128					   struct fsverity_descriptor *desc);
129
130void fsverity_set_info(struct inode *inode, struct fsverity_info *vi);
131
132void fsverity_free_info(struct fsverity_info *vi);
133
134int fsverity_get_descriptor(struct inode *inode,
135			    struct fsverity_descriptor **desc_ret);
136
137void __init fsverity_init_info_cache(void);
138
139/* signature.c */
140
141#ifdef CONFIG_FS_VERITY_BUILTIN_SIGNATURES
142extern int fsverity_require_signatures;
143int fsverity_verify_signature(const struct fsverity_info *vi,
144			      const u8 *signature, size_t sig_size);
145
146void __init fsverity_init_signature(void);
147#else /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */
148static inline int
149fsverity_verify_signature(const struct fsverity_info *vi,
150			  const u8 *signature, size_t sig_size)
151{
152	return 0;
153}
154
155static inline void fsverity_init_signature(void)
156{
157}
158#endif /* !CONFIG_FS_VERITY_BUILTIN_SIGNATURES */
159
160/* verify.c */
161
162void __init fsverity_init_workqueue(void);
163
164#endif /* _FSVERITY_PRIVATE_H */