Date:   Wed, 27 Jan 2021 19:14:10 -0500
From:   Stefan Berger <stefanb@...ux.vnet.ibm.com>
To:     keyrings@...r.kernel.org, linux-crypto@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, patrick@...terwijk.org,
        Stefan Berger <stefanb@...ux.ibm.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH v4 1/3] crypto: Add support for ECDSA signature verification

From: Stefan Berger <stefanb@...ux.ibm.com>

Add support for parsing the parameters of a NIST P256 or NIST P192 key.
Enable signature verification using these keys.

Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: linux-crypto@...r.kernel.org
---
 crypto/Makefile            |   9 +-
 crypto/ecc.c               | 279 +++++++++++++++++++++++++++++++++++++
 crypto/ecc.h               |   2 +
 crypto/ecdsasignature.asn1 |   4 +
 4 files changed, 293 insertions(+), 1 deletion(-)
 create mode 100644 crypto/ecdsasignature.asn1

diff --git a/crypto/Makefile b/crypto/Makefile
index b279483fba50..767f6b71aa20 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -50,6 +50,14 @@ sm2_generic-y += sm2.o
 
 obj-$(CONFIG_CRYPTO_SM2) += sm2_generic.o
 
+$(obj)/ecdsasignature.asn1.o: $(obj)/ecdsasignature.asn1.c $(obj)/ecdsasignature.asn1.h
+$(obj)/ecc.o: $(obj)/ecdsasignature.asn1.h
+
+ecc_generic-y += ecdsasignature.asn1.o
+ecc_generic-y += ecc.o
+
+obj-$(CONFIG_CRYPTO_ECC) += ecc_generic.o
+
 crypto_acompress-y := acompress.o
 crypto_acompress-y += scompress.o
 obj-$(CONFIG_CRYPTO_ACOMP2) += crypto_acompress.o
@@ -172,7 +180,6 @@ obj-$(CONFIG_CRYPTO_USER_API_RNG) += algif_rng.o
 obj-$(CONFIG_CRYPTO_USER_API_AEAD) += algif_aead.o
 obj-$(CONFIG_CRYPTO_ZSTD) += zstd.o
 obj-$(CONFIG_CRYPTO_OFB) += ofb.o
-obj-$(CONFIG_CRYPTO_ECC) += ecc.o
 obj-$(CONFIG_CRYPTO_ESSIV) += essiv.o
 obj-$(CONFIG_CRYPTO_CURVE25519) += curve25519-generic.o
 
diff --git a/crypto/ecc.c b/crypto/ecc.c
index c80aa25994a0..3636f9d17eaf 100644
--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -29,13 +29,18 @@
 #include <linux/slab.h>
 #include <linux/swab.h>
 #include <linux/fips.h>
+#include <crypto/internal/akcipher.h>
+#include <crypto/akcipher.h>
 #include <crypto/ecdh.h>
 #include <crypto/rng.h>
 #include <asm/unaligned.h>
 #include <linux/ratelimit.h>
+#include <linux/asn1_decoder.h>
+#include <linux/scatterlist.h>
 
 #include "ecc.h"
 #include "ecc_curve_defs.h"
+#include "ecdsasignature.asn1.h"
 
 typedef struct {
 	u64 m_low;
@@ -1542,4 +1547,278 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
 }
 EXPORT_SYMBOL(crypto_ecdh_shared_secret);
 
+struct ecc_ctx {
+	const struct ecc_curve *curve;
+	struct ecc_point *pub_key;
+};
+
+struct ecdsa_signature_ctx {
+	const struct ecc_curve *curve;
+	u64 r[ECC_MAX_DIGITS];
+	u64 s[ECC_MAX_DIGITS];
+};
+
+/*
+ * Get the r and s components of a signature from the X509 certificate.
+ */
+static int ecdsa_get_signature_rs(u64 *dest, size_t hdrlen, unsigned char tag,
+				  const void *value, size_t vlen,
+				  unsigned int ndigits)
+{
+	size_t keylen = ndigits * sizeof(u64);
+	ssize_t diff = vlen - keylen;
+	const char *d = value;
+	u8 rs[ECC_MAX_BYTES];
+
+	if (!value || !vlen)
+		return -EINVAL;
+
+	/* diff = 0: 'value' has exacly the right size
+	 * diff > 0: 'value' has too many bytes; one leading zero is allowed that
+	 *           makes the value a positive integer; error on more
+	 * diff < 0: 'value' is missing leading zeros, which we add
+	 */
+	if (diff > 0) {
+		/* skip over leading zeros that make 'value' a positive int */
+		if (*d == 0) {
+			vlen -= 1;
+			diff--;
+			d++;
+		}
+		if (diff)
+			return -EINVAL;
+	}
+	if (-diff >= keylen)
+		return -EINVAL;
+
+	if (diff) {
+		/* leading zeros not given in 'value' */
+		memset(rs, 0, -diff);
+	}
+
+	memcpy(&rs[-diff], d, vlen);
+
+	ecc_swap_digits((u64 *)rs, dest, ndigits);
+
+	return 0;
+}
+
+int ecdsa_get_signature_r(void *context, size_t hdrlen, unsigned char tag,
+			const void *value, size_t vlen)
+{
+	struct ecdsa_signature_ctx *sig = context;
+
+	return ecdsa_get_signature_rs(sig->r, hdrlen, tag, value, vlen,
+				      sig->curve->g.ndigits);
+}
+
+int ecdsa_get_signature_s(void *context, size_t hdrlen, unsigned char tag,
+			  const void *value, size_t vlen)
+{
+	struct ecdsa_signature_ctx *sig = context;
+
+	return ecdsa_get_signature_rs(sig->s, hdrlen, tag, value, vlen,
+				      sig->curve->g.ndigits);
+}
+
+static int _ecdsa_verify(struct ecc_ctx *ctx, const u64 *hash,
+			 const u64 *r, const u64 *s)
+{
+	const struct ecc_curve *curve = ctx->curve;
+	unsigned int ndigits = curve->g.ndigits;
+	u64 s1[ECC_MAX_DIGITS];
+	u64 u1[ECC_MAX_DIGITS];
+	u64 u2[ECC_MAX_DIGITS];
+	u64 x1[ECC_MAX_DIGITS];
+	u64 y1[ECC_MAX_DIGITS];
+	struct ecc_point res = ECC_POINT_INIT(x1, y1, ndigits);
+
+	/* 0 < r < n  and 0 < s < n */
+	if (vli_is_zero(r, ndigits) || vli_cmp(r, curve->n, ndigits) >= 0 ||
+	    vli_is_zero(s, ndigits) || vli_cmp(s, curve->n, ndigits) >= 0)
+		return -EBADMSG;
+
+	/* hash is given */
+	pr_devel("hash : %016llx %016llx ... %016llx\n",
+		 hash[ndigits - 1], hash[ndigits - 2], hash[0]);
+
+	/* s1 = (s^-1) mod n */
+	vli_mod_inv(s1, s, curve->n, ndigits);
+	/* u1 = (hash * s1) mod n */
+	vli_mod_mult_slow(u1, hash, s1, curve->n, ndigits);
+	/* u2 = (r * s1) mod n */
+	vli_mod_mult_slow(u2, r, s1, curve->n, ndigits);
+	/* res = u1*G + u2 * pub_key */
+	ecc_point_mult_shamir(&res, u1, &curve->g, u2, ctx->pub_key, curve);
+
+	/* res.x = res.x mod n (if res.x > order) */
+	if (unlikely(vli_cmp(res.x, curve->n, ndigits) == 1))
+		/* faster alternative for NIST p256 & p192 */
+		vli_sub(res.x, res.x, curve->n, ndigits);
+
+	if (!vli_cmp(res.x, r, ndigits))
+		return 0;
+
+	return -EKEYREJECTED;
+}
+
+/*
+ * Verify an ECDSA signature.
+ */
+static int ecdsa_verify(struct akcipher_request *req)
+{
+	struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
+	struct ecc_ctx *ctx = akcipher_tfm_ctx(tfm);
+	size_t keylen = ctx->curve->g.ndigits * sizeof(u64);
+	struct ecdsa_signature_ctx sig_ctx = {
+		.curve = ctx->curve,
+	};
+	u8 rawhash[ECC_MAX_BYTES];
+	u64 hash[ECC_MAX_DIGITS];
+	unsigned char *buffer;
+	ssize_t diff;
+	int ret;
+
+	if (unlikely(!ctx->pub_key))
+		return -EINVAL;
+
+	buffer = kmalloc(req->src_len + req->dst_len, GFP_KERNEL);
+	if (!buffer)
+		return -ENOMEM;
+
+	sg_pcopy_to_buffer(req->src,
+		sg_nents_for_len(req->src, req->src_len + req->dst_len),
+		buffer, req->src_len + req->dst_len, 0);
+
+	ret = asn1_ber_decoder(&ecdsasignature_decoder, &sig_ctx,
+			       buffer, req->src_len);
+	if (ret < 0)
+		goto error;
+
+	/* if the hash is shorter then we will add leading zeros to fit to ndigits */
+	diff = keylen - req->dst_len;
+	if (diff >= 0) {
+		if (diff)
+			memset(rawhash, 0, diff);
+		memcpy(&rawhash[diff], buffer + req->src_len, req->dst_len);
+	} else if (diff < 0) {
+		/* given hash is longer, we take the left-most bytes */
+		memcpy(&rawhash, buffer + req->src_len, keylen);
+	}
+
+	ecc_swap_digits((u64 *)rawhash, hash, ctx->curve->g.ndigits);
+
+	ret = _ecdsa_verify(ctx, hash, sig_ctx.r, sig_ctx.s);
+
+error:
+	kfree(buffer);
+
+	return ret;
+}
+
+static void ecdsa_ec_ctx_deinit(struct ecc_ctx *ctx)
+{
+	ecc_free_point(ctx->pub_key);
+	ctx->pub_key = NULL;
+}
+
+static int ecdsa_ec_ctx_reset(struct ecc_ctx *ctx)
+{
+	ecdsa_ec_ctx_deinit(ctx);
+	return 0;
+}
+
+/*
+ * Set the public key given the raw uncompressed key data from an X509
+ * certificate. The key data contain the concatenated X and Y coordinates of
+ * the public key.
+ */
+static int ecdsa_set_pub_key(struct crypto_akcipher *tfm,
+			     const void *key, unsigned int keylen)
+{
+	struct ecc_ctx *ctx = akcipher_tfm_ctx(tfm);
+	const unsigned char *d = key;
+	const u64 *digits = (const u64 *)&d[1];
+	unsigned int ndigits;
+	int ret;
+
+	ret = ecdsa_ec_ctx_reset(ctx);
+	if (ret < 0)
+		return ret;
+
+	if (keylen < 1 || (((keylen - 1) >> 1) % sizeof(u64)) != 0)
+		return -EINVAL;
+	/* we only accept uncompressed format */
+	if (d[0] != 4)
+		return -EINVAL;
+
+	keylen--;
+	ndigits = (keylen >> 1) / sizeof(u64);
+	switch (ndigits) {
+	case 3:
+		ctx->curve = ecc_get_curve(ECC_CURVE_NIST_P192);
+		break;
+	case 4:
+		ctx->curve = ecc_get_curve(ECC_CURVE_NIST_P256);
+		break;
+	}
+	if (!ctx->curve)
+		return -EINVAL;
+
+	ctx->pub_key = ecc_alloc_point(ndigits);
+	if (!ctx->pub_key)
+		return -ENOMEM;
+
+	ecc_swap_digits(digits, ctx->pub_key->x, ndigits);
+	ecc_swap_digits(&digits[ndigits], ctx->pub_key->y, ndigits);
+	return ecc_is_pubkey_valid_full(ctx->curve, ctx->pub_key);
+}
+
+static void ecdsa_exit_tfm(struct crypto_akcipher *tfm)
+{
+	struct ecc_ctx *ctx = akcipher_tfm_ctx(tfm);
+
+	ecdsa_ec_ctx_deinit(ctx);
+}
+
+static unsigned int ecdsa_max_size(struct crypto_akcipher *tfm)
+{
+	struct ecc_ctx *ctx = akcipher_tfm_ctx(tfm);
+
+	return ctx->pub_key->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
+}
+
+static int ecdsa_init_tfm(struct crypto_akcipher *tfm)
+{
+	return 0;
+}
+
+static struct akcipher_alg ecdsa = {
+	.verify = ecdsa_verify,
+	.set_pub_key = ecdsa_set_pub_key,
+	.max_size = ecdsa_max_size,
+	.init = ecdsa_init_tfm,
+	.exit = ecdsa_exit_tfm,
+	.base = {
+		.cra_name = "ecdsa",
+		.cra_driver_name = "ecdsa-generic",
+		.cra_priority = 100,
+		.cra_module = THIS_MODULE,
+		.cra_ctxsize = sizeof(struct ecc_ctx),
+	},
+};
+
+static int ecdsa_init(void)
+{
+	return crypto_register_akcipher(&ecdsa);
+}
+
+static void ecdsa_exit(void)
+{
+	crypto_unregister_akcipher(&ecdsa);
+}
+
+subsys_initcall(ecdsa_init);
+module_exit(ecdsa_exit);
+
 MODULE_LICENSE("Dual BSD/GPL");
diff --git a/crypto/ecc.h b/crypto/ecc.h
index d4e546b9ad79..26d7c83908bc 100644
--- a/crypto/ecc.h
+++ b/crypto/ecc.h
@@ -33,6 +33,8 @@
 
 #define ECC_DIGITS_TO_BYTES_SHIFT 3
 
+#define ECC_MAX_BYTES (ECC_MAX_DIGITS << ECC_DIGITS_TO_BYTES_SHIFT)
+
 /**
  * struct ecc_point - elliptic curve point in affine coordinates
  *
diff --git a/crypto/ecdsasignature.asn1 b/crypto/ecdsasignature.asn1
new file mode 100644
index 000000000000..621ab754fb9f
--- /dev/null
+++ b/crypto/ecdsasignature.asn1
@@ -0,0 +1,4 @@
+ECDSASignature ::= SEQUENCE {
+	r	INTEGER ({ ecdsa_get_signature_r }),
+	s	INTEGER ({ ecdsa_get_signature_s })
+}
-- 
2.26.2

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