1// SPDX-License-Identifier: GPL-2.0
2/*
3 * fs-verity hash algorithms
4 *
5 * Copyright 2019 Google LLC
6 */
7
8#include "fsverity_private.h"
9
10/* The hash algorithms supported by fs-verity */
11const struct fsverity_hash_alg fsverity_hash_algs[] = {
12 [FS_VERITY_HASH_ALG_SHA256] = {
13 .name = "sha256",
14 .digest_size = SHA256_DIGEST_SIZE,
15 .block_size = SHA256_BLOCK_SIZE,
16 .algo_id = HASH_ALGO_SHA256,
17 },
18 [FS_VERITY_HASH_ALG_SHA512] = {
19 .name = "sha512",
20 .digest_size = SHA512_DIGEST_SIZE,
21 .block_size = SHA512_BLOCK_SIZE,
22 .algo_id = HASH_ALGO_SHA512,
23 },
24};
25
26/**
27 * fsverity_get_hash_alg() - get a hash algorithm by number
28 * @inode: optional inode for logging purposes
29 * @num: the hash algorithm number
30 *
31 * Get the struct fsverity_hash_alg for the given hash algorithm number.
32 *
33 * Return: pointer to the hash alg if it's known, otherwise NULL.
34 */
35const struct fsverity_hash_alg *fsverity_get_hash_alg(const struct inode *inode,
36 unsigned int num)
37{
38 if (num >= ARRAY_SIZE(fsverity_hash_algs) ||
39 !fsverity_hash_algs[num].name) {
40 fsverity_warn(inode, "Unknown hash algorithm number: %u", num);
41 return NULL;
42 }
43 return &fsverity_hash_algs[num];
44}
45
46/**
47 * fsverity_prepare_hash_state() - precompute the initial hash state
48 * @alg: hash algorithm
49 * @salt: a salt which is to be prepended to all data to be hashed
50 * @salt_size: salt size in bytes
51 *
52 * Return: the kmalloc()'ed initial hash state, or NULL if out of memory.
53 */
54union fsverity_hash_ctx *
55fsverity_prepare_hash_state(const struct fsverity_hash_alg *alg,
56 const u8 *salt, size_t salt_size)
57{
58 u8 *padded_salt = NULL;
59 size_t padded_salt_size;
60 union fsverity_hash_ctx ctx;
61 void *res = NULL;
62
63 /*
64 * Zero-pad the salt to the next multiple of the input size of the hash
65 * algorithm's compression function, e.g. 64 bytes for SHA-256 or 128
66 * bytes for SHA-512. This ensures that the hash algorithm won't have
67 * any bytes buffered internally after processing the salt, thus making
68 * salted hashing just as fast as unsalted hashing.
69 */
70 padded_salt_size = round_up(salt_size, alg->block_size);
71 padded_salt = kzalloc(padded_salt_size, GFP_KERNEL);
72 if (!padded_salt)
73 return NULL;
74 memcpy(padded_salt, salt, salt_size);
75
76 switch (alg->algo_id) {
77 case HASH_ALGO_SHA256:
78 sha256_init(ctx: &ctx.sha256);
79 sha256_update(ctx: &ctx.sha256, data: padded_salt, len: padded_salt_size);
80 res = kmemdup(&ctx.sha256, sizeof(ctx.sha256), GFP_KERNEL);
81 break;
82 case HASH_ALGO_SHA512:
83 sha512_init(ctx: &ctx.sha512);
84 sha512_update(ctx: &ctx.sha512, data: padded_salt, len: padded_salt_size);
85 res = kmemdup(&ctx.sha512, sizeof(ctx.sha512), GFP_KERNEL);
86 break;
87 default:
88 WARN_ON_ONCE(1);
89 }
90 kfree(objp: padded_salt);
91 return res;
92}
93
94/**
95 * fsverity_hash_block() - hash a single data or hash block
96 * @params: the Merkle tree's parameters
97 * @data: virtual address of a buffer containing the block to hash
98 * @out: output digest, size 'params->digest_size' bytes
99 *
100 * Hash a single data or hash block. The hash is salted if a salt is specified
101 * in the Merkle tree parameters.
102 */
103void fsverity_hash_block(const struct merkle_tree_params *params,
104 const void *data, u8 *out)
105{
106 union fsverity_hash_ctx ctx;
107
108 if (!params->hashstate) {
109 fsverity_hash_buffer(alg: params->hash_alg, data, size: params->block_size,
110 out);
111 return;
112 }
113
114 switch (params->hash_alg->algo_id) {
115 case HASH_ALGO_SHA256:
116 ctx.sha256 = params->hashstate->sha256;
117 sha256_update(ctx: &ctx.sha256, data, len: params->block_size);
118 sha256_final(ctx: &ctx.sha256, out);
119 return;
120 case HASH_ALGO_SHA512:
121 ctx.sha512 = params->hashstate->sha512;
122 sha512_update(ctx: &ctx.sha512, data, len: params->block_size);
123 sha512_final(ctx: &ctx.sha512, out);
124 return;
125 default:
126 BUG();
127 }
128}
129
130/**
131 * fsverity_hash_buffer() - hash some data
132 * @alg: the hash algorithm to use
133 * @data: the data to hash
134 * @size: size of data to hash, in bytes
135 * @out: output digest, size 'alg->digest_size' bytes
136 */
137void fsverity_hash_buffer(const struct fsverity_hash_alg *alg,
138 const void *data, size_t size, u8 *out)
139{
140 switch (alg->algo_id) {
141 case HASH_ALGO_SHA256:
142 sha256(data, len: size, out);
143 return;
144 case HASH_ALGO_SHA512:
145 sha512(data, len: size, out);
146 return;
147 default:
148 BUG();
149 }
150}
151
152void __init fsverity_check_hash_algs(void)
153{
154 size_t i;
155
156 /*
157 * Sanity check the hash algorithms (could be a build-time check, but
158 * they're in an array)
159 */
160 for (i = 0; i < ARRAY_SIZE(fsverity_hash_algs); i++) {
161 const struct fsverity_hash_alg *alg = &fsverity_hash_algs[i];
162
163 if (!alg->name)
164 continue;
165
166 /*
167 * 0 must never be allocated as an FS_VERITY_HASH_ALG_* value,
168 * as it is reserved for users that use 0 to mean unspecified or
169 * a default value. fs/verity/ itself doesn't care and doesn't
170 * have a default algorithm, but some users make use of this.
171 */
172 BUG_ON(i == 0);
173
174 BUG_ON(alg->digest_size > FS_VERITY_MAX_DIGEST_SIZE);
175
176 /*
177 * For efficiency, the implementation currently assumes the
178 * digest and block sizes are powers of 2. This limitation can
179 * be lifted if the code is updated to handle other values.
180 */
181 BUG_ON(!is_power_of_2(alg->digest_size));
182 BUG_ON(!is_power_of_2(alg->block_size));
183
184 /* Verify that there is a valid mapping to HASH_ALGO_*. */
185 BUG_ON(alg->algo_id == 0);
186 BUG_ON(alg->digest_size != hash_digest_size[alg->algo_id]);
187 }
188}
189

source code of linux/fs/verity/hash_algs.c