1 // SPDX-License-Identifier: GPL-2.0 OR MIT
2 /*
3  * Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All Rights Reserved.
4  *
5  * Based on public domain code from Daniel J. Bernstein and Peter Schwabe. This
6  * began from SUPERCOP's curve25519/neon2/scalarmult.s, but has subsequently been
7  * manually reworked for use in kernel space.
8  */
9 
10 #include <asm/hwcap.h>
11 #include <asm/neon.h>
12 #include <asm/simd.h>
13 #include <crypto/internal/kpp.h>
14 #include <crypto/internal/simd.h>
15 #include <linux/types.h>
16 #include <linux/module.h>
17 #include <linux/init.h>
18 #include <linux/jump_label.h>
19 #include <linux/scatterlist.h>
20 #include <crypto/curve25519.h>
21 
22 asmlinkage void curve25519_neon(u8 mypublic[CURVE25519_KEY_SIZE],
23 				const u8 secret[CURVE25519_KEY_SIZE],
24 				const u8 basepoint[CURVE25519_KEY_SIZE]);
25 
26 static __ro_after_init DEFINE_STATIC_KEY_FALSE(have_neon);
27 
28 void curve25519_arch(u8 out[CURVE25519_KEY_SIZE],
29 		     const u8 scalar[CURVE25519_KEY_SIZE],
30 		     const u8 point[CURVE25519_KEY_SIZE])
31 {
32 	if (static_branch_likely(&have_neon) && crypto_simd_usable()) {
33 		kernel_neon_begin();
34 		curve25519_neon(out, scalar, point);
35 		kernel_neon_end();
36 	} else {
37 		curve25519_generic(out, scalar, point);
38 	}
39 }
40 EXPORT_SYMBOL(curve25519_arch);
41 
42 void curve25519_base_arch(u8 pub[CURVE25519_KEY_SIZE],
43 			  const u8 secret[CURVE25519_KEY_SIZE])
44 {
45 	return curve25519_arch(pub, secret, curve25519_base_point);
46 }
47 EXPORT_SYMBOL(curve25519_base_arch);
48 
49 static int curve25519_set_secret(struct crypto_kpp *tfm, const void *buf,
50 				 unsigned int len)
51 {
52 	u8 *secret = kpp_tfm_ctx(tfm);
53 
54 	if (!len)
55 		curve25519_generate_secret(secret);
56 	else if (len == CURVE25519_KEY_SIZE &&
57 		 crypto_memneq(buf, curve25519_null_point, CURVE25519_KEY_SIZE))
58 		memcpy(secret, buf, CURVE25519_KEY_SIZE);
59 	else
60 		return -EINVAL;
61 	return 0;
62 }
63 
64 static int curve25519_compute_value(struct kpp_request *req)
65 {
66 	struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
67 	const u8 *secret = kpp_tfm_ctx(tfm);
68 	u8 public_key[CURVE25519_KEY_SIZE];
69 	u8 buf[CURVE25519_KEY_SIZE];
70 	int copied, nbytes;
71 	u8 const *bp;
72 
73 	if (req->src) {
74 		copied = sg_copy_to_buffer(req->src,
75 					   sg_nents_for_len(req->src,
76 							    CURVE25519_KEY_SIZE),
77 					   public_key, CURVE25519_KEY_SIZE);
78 		if (copied != CURVE25519_KEY_SIZE)
79 			return -EINVAL;
80 		bp = public_key;
81 	} else {
82 		bp = curve25519_base_point;
83 	}
84 
85 	curve25519_arch(buf, secret, bp);
86 
87 	/* might want less than we've got */
88 	nbytes = min_t(size_t, CURVE25519_KEY_SIZE, req->dst_len);
89 	copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst,
90 								nbytes),
91 				     buf, nbytes);
92 	if (copied != nbytes)
93 		return -EINVAL;
94 	return 0;
95 }
96 
97 static unsigned int curve25519_max_size(struct crypto_kpp *tfm)
98 {
99 	return CURVE25519_KEY_SIZE;
100 }
101 
102 static struct kpp_alg curve25519_alg = {
103 	.base.cra_name		= "curve25519",
104 	.base.cra_driver_name	= "curve25519-neon",
105 	.base.cra_priority	= 200,
106 	.base.cra_module	= THIS_MODULE,
107 	.base.cra_ctxsize	= CURVE25519_KEY_SIZE,
108 
109 	.set_secret		= curve25519_set_secret,
110 	.generate_public_key	= curve25519_compute_value,
111 	.compute_shared_secret	= curve25519_compute_value,
112 	.max_size		= curve25519_max_size,
113 };
114 
115 static int __init mod_init(void)
116 {
117 	if (elf_hwcap & HWCAP_NEON) {
118 		static_branch_enable(&have_neon);
119 		return IS_REACHABLE(CONFIG_CRYPTO_KPP) ?
120 			crypto_register_kpp(&curve25519_alg) : 0;
121 	}
122 	return 0;
123 }
124 
125 static void __exit mod_exit(void)
126 {
127 	if (IS_REACHABLE(CONFIG_CRYPTO_KPP) && elf_hwcap & HWCAP_NEON)
128 		crypto_unregister_kpp(&curve25519_alg);
129 }
130 
131 module_init(mod_init);
132 module_exit(mod_exit);
133 
134 MODULE_ALIAS_CRYPTO("curve25519");
135 MODULE_ALIAS_CRYPTO("curve25519-neon");
136 MODULE_LICENSE("GPL v2");
137