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 <crypto/curve25519.h>
20 
21 asmlinkage void curve25519_neon(u8 mypublic[CURVE25519_KEY_SIZE],
22 				const u8 secret[CURVE25519_KEY_SIZE],
23 				const u8 basepoint[CURVE25519_KEY_SIZE]);
24 
25 static __ro_after_init DEFINE_STATIC_KEY_FALSE(have_neon);
26 
27 void curve25519_arch(u8 out[CURVE25519_KEY_SIZE],
28 		     const u8 scalar[CURVE25519_KEY_SIZE],
29 		     const u8 point[CURVE25519_KEY_SIZE])
30 {
31 	if (static_branch_likely(&have_neon) && crypto_simd_usable()) {
32 		kernel_neon_begin();
33 		curve25519_neon(out, scalar, point);
34 		kernel_neon_end();
35 	} else {
36 		curve25519_generic(out, scalar, point);
37 	}
38 }
39 EXPORT_SYMBOL(curve25519_arch);
40 
41 static int curve25519_set_secret(struct crypto_kpp *tfm, const void *buf,
42 				 unsigned int len)
43 {
44 	u8 *secret = kpp_tfm_ctx(tfm);
45 
46 	if (!len)
47 		curve25519_generate_secret(secret);
48 	else if (len == CURVE25519_KEY_SIZE &&
49 		 crypto_memneq(buf, curve25519_null_point, CURVE25519_KEY_SIZE))
50 		memcpy(secret, buf, CURVE25519_KEY_SIZE);
51 	else
52 		return -EINVAL;
53 	return 0;
54 }
55 
56 static int curve25519_compute_value(struct kpp_request *req)
57 {
58 	struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
59 	const u8 *secret = kpp_tfm_ctx(tfm);
60 	u8 public_key[CURVE25519_KEY_SIZE];
61 	u8 buf[CURVE25519_KEY_SIZE];
62 	int copied, nbytes;
63 	u8 const *bp;
64 
65 	if (req->src) {
66 		copied = sg_copy_to_buffer(req->src,
67 					   sg_nents_for_len(req->src,
68 							    CURVE25519_KEY_SIZE),
69 					   public_key, CURVE25519_KEY_SIZE);
70 		if (copied != CURVE25519_KEY_SIZE)
71 			return -EINVAL;
72 		bp = public_key;
73 	} else {
74 		bp = curve25519_base_point;
75 	}
76 
77 	curve25519_arch(buf, secret, bp);
78 
79 	/* might want less than we've got */
80 	nbytes = min_t(size_t, CURVE25519_KEY_SIZE, req->dst_len);
81 	copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst,
82 								nbytes),
83 				     buf, nbytes);
84 	if (copied != nbytes)
85 		return -EINVAL;
86 	return 0;
87 }
88 
89 static unsigned int curve25519_max_size(struct crypto_kpp *tfm)
90 {
91 	return CURVE25519_KEY_SIZE;
92 }
93 
94 static struct kpp_alg curve25519_alg = {
95 	.base.cra_name		= "curve25519",
96 	.base.cra_driver_name	= "curve25519-neon",
97 	.base.cra_priority	= 200,
98 	.base.cra_module	= THIS_MODULE,
99 	.base.cra_ctxsize	= CURVE25519_KEY_SIZE,
100 
101 	.set_secret		= curve25519_set_secret,
102 	.generate_public_key	= curve25519_compute_value,
103 	.compute_shared_secret	= curve25519_compute_value,
104 	.max_size		= curve25519_max_size,
105 };
106 
107 static int __init mod_init(void)
108 {
109 	if (elf_hwcap & HWCAP_NEON) {
110 		static_branch_enable(&have_neon);
111 		return IS_REACHABLE(CONFIG_CRYPTO_KPP) ?
112 			crypto_register_kpp(&curve25519_alg) : 0;
113 	}
114 	return 0;
115 }
116 
117 static void __exit mod_exit(void)
118 {
119 	if (IS_REACHABLE(CONFIG_CRYPTO_KPP) && elf_hwcap & HWCAP_NEON)
120 		crypto_unregister_kpp(&curve25519_alg);
121 }
122 
123 module_init(mod_init);
124 module_exit(mod_exit);
125 
126 MODULE_ALIAS_CRYPTO("curve25519");
127 MODULE_ALIAS_CRYPTO("curve25519-neon");
128 MODULE_LICENSE("GPL v2");
129