lib: Add support for ECDSA image signing

mkimage supports rsa2048, and rsa4096 signatures. With newer silicon
now supporting hardware-accelerated ECDSA, it makes sense to expand
signing support to elliptic curves.

Implement host-side ECDSA signing and verification with libcrypto.
Device-side implementation of signature verification is beyond the
scope of this patch.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

5 files changed, 415 insertions, 2 deletions

diff --git a/common/image-sig.c b/common/image-sig.c
index 54f0eb2019..0f8e592aba 100644
--- a/common/image-sig.c
+++ b/common/image-sig.c
@@ -16,6 +16,7 @@
 DECLARE_GLOBAL_DATA_PTR;
 #endif /* !USE_HOSTCC*/
 #include <image.h>
+#include <u-boot/ecdsa.h>
 #include <u-boot/rsa.h>
 #include <u-boot/hash-checksum.h>
 
@@ -83,8 +84,14 @@ struct crypto_algo crypto_algos[] = {
 		.sign = rsa_sign,
 		.add_verify_data = rsa_add_verify_data,
 		.verify = rsa_verify,
-	}
-
+	},
+	{
+		.name = "ecdsa256",
+		.key_len = ECDSA256_BYTES,
+		.sign = ecdsa_sign,
+		.add_verify_data = ecdsa_add_verify_data,
+		.verify = ecdsa_verify,
+	},
 };
 
 struct padding_algo padding_algos[] = {
diff --git a/include/image.h b/include/image.h
index 375fb46bf9..f172b1224d 100644
--- a/include/image.h
+++ b/include/image.h
@@ -1224,16 +1224,19 @@ int calculate_hash(const void *data, int data_len, const char *algo,
 # if defined(CONFIG_FIT_SIGNATURE)
 #  define IMAGE_ENABLE_SIGN	1
 #  define IMAGE_ENABLE_VERIFY	1
+#  define IMAGE_ENABLE_VERIFY_ECDSA	1
 #  define FIT_IMAGE_ENABLE_VERIFY	1
 #  include <openssl/evp.h>
 # else
 #  define IMAGE_ENABLE_SIGN	0
 #  define IMAGE_ENABLE_VERIFY	0
+# define IMAGE_ENABLE_VERIFY_ECDSA	0
 #  define FIT_IMAGE_ENABLE_VERIFY	0
 # endif
 #else
 # define IMAGE_ENABLE_SIGN	0
 # define IMAGE_ENABLE_VERIFY		CONFIG_IS_ENABLED(RSA_VERIFY)
+# define IMAGE_ENABLE_VERIFY_ECDSA	0
 # define FIT_IMAGE_ENABLE_VERIFY	CONFIG_IS_ENABLED(FIT_SIGNATURE)
 #endif
 
diff --git a/include/u-boot/ecdsa.h b/include/u-boot/ecdsa.h
new file mode 100644
index 0000000000..979690d966
--- /dev/null
+++ b/include/u-boot/ecdsa.h
@@ -0,0 +1,94 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (c) 2020, Alexandru Gagniuc <mr.nuke.me@gmail.com>.
+ */
+
+#ifndef _ECDSA_H
+#define _ECDSA_H
+
+#include <errno.h>
+#include <image.h>
+#include <linux/kconfig.h>
+
+/**
+ * crypto_algo API impementation for ECDSA;
+ * @see "struct crypto_algo"
+ * @{
+ */
+#if IMAGE_ENABLE_SIGN
+/**
+ * sign() - calculate and return signature for given input data
+ *
+ * @info:	Specifies key and FIT information
+ * @data:	Pointer to the input data
+ * @data_len:	Data length
+ * @sigp:	Set to an allocated buffer holding the signature
+ * @sig_len:	Set to length of the calculated hash
+ *
+ * This computes input data signature according to selected algorithm.
+ * Resulting signature value is placed in an allocated buffer, the
+ * pointer is returned as *sigp. The length of the calculated
+ * signature is returned via the sig_len pointer argument. The caller
+ * should free *sigp.
+ *
+ * @return: 0, on success, -ve on error
+ */
+int ecdsa_sign(struct image_sign_info *info, const struct image_region region[],
+	       int region_count, uint8_t **sigp, uint *sig_len);
+
+/**
+ * add_verify_data() - Add verification information to FDT
+ *
+ * Add public key information to the FDT node, suitable for
+ * verification at run-time. The information added depends on the
+ * algorithm being used. I just copypasted this from rsa.h.
+ *
+ * @info:	Specifies key and FIT information
+ * @keydest:	Destination FDT blob for public key data
+ * @return: 0, on success, -ENOSPC if the keydest FDT blob ran out of space,
+ * other -ve value on error
+ */
+int ecdsa_add_verify_data(struct image_sign_info *info, void *keydest);
+#else
+static inline
+int ecdsa_sign(struct image_sign_info *info, const struct image_region region[],
+	       int region_count, uint8_t **sigp, uint *sig_len)
+{
+	return -ENXIO;
+}
+
+static inline
+int ecdsa_add_verify_data(struct image_sign_info *info, void *keydest)
+{
+	return -ENXIO;
+}
+#endif
+
+#if IMAGE_ENABLE_VERIFY_ECDSA
+/**
+ * verify() - Verify a signature against some data
+ *
+ * @info:	Specifies key and FIT information
+ * @data:	Pointer to the input data
+ * @data_len:	Data length
+ * @sig:	Signature
+ * @sig_len:	Number of bytes in signature
+ * @return 0 if verified, -ve on error
+ */
+int ecdsa_verify(struct image_sign_info *info,
+		 const struct image_region region[], int region_count,
+		 uint8_t *sig, uint sig_len);
+#else
+static inline
+int ecdsa_verify(struct image_sign_info *info,
+		 const struct image_region region[], int region_count,
+		 uint8_t *sig, uint sig_len)
+{
+	return -ENXIO;
+}
+#endif
+/** @} */
+
+#define ECDSA256_BYTES	(256 / 8)
+
+#endif
diff --git a/lib/ecdsa/ecdsa-libcrypto.c b/lib/ecdsa/ecdsa-libcrypto.c
new file mode 100644
index 0000000000..322880963f
--- /dev/null
+++ b/lib/ecdsa/ecdsa-libcrypto.c
@@ -0,0 +1,306 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * ECDSA image signing implementation using libcrypto backend
+ *
+ * The signature is a binary representation of the (R, S) points, padded to the
+ * key size. The signature will be (2 * key_size_bits) / 8 bytes.
+ *
+ * Deviations from behavior of RSA equivalent:
+ *  - Verification uses private key. This is not technically required, but a
+ *    limitation on how clumsy the openssl API is to use.
+ *  - Handling of keys and key paths:
+ *    - The '-K' key directory option must contain path to the key file,
+ *      instead of the key directory.
+ *    - No assumptions are made about the file extension of the key
+ *    - The 'key-name-hint' property is only used for naming devicetree nodes,
+ *      but is not used for looking up keys on the filesystem.
+ *
+ * Copyright (c) 2020,2021, Alexandru Gagniuc <mr.nuke.me@gmail.com>
+ */
+
+#include <u-boot/ecdsa.h>
+#include <u-boot/fdt-libcrypto.h>
+#include <openssl/ssl.h>
+#include <openssl/ec.h>
+#include <openssl/bn.h>
+
+/* Image signing context for openssl-libcrypto */
+struct signer {
+	EVP_PKEY *evp_key;	/* Pointer to EVP_PKEY object */
+	EC_KEY *ecdsa_key;	/* Pointer to EC_KEY object */
+	void *hash;		/* Pointer to hash used for verification */
+	void *signature;	/* Pointer to output signature. Do not free()!*/
+};
+
+static int alloc_ctx(struct signer *ctx, const struct image_sign_info *info)
+{
+	memset(ctx, 0, sizeof(*ctx));
+
+	if (!OPENSSL_init_ssl(0, NULL)) {
+		fprintf(stderr, "Failure to init SSL library\n");
+		return -1;
+	}
+
+	ctx->hash = malloc(info->checksum->checksum_len);
+	ctx->signature = malloc(info->crypto->key_len * 2);
+
+	if (!ctx->hash || !ctx->signature)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static void free_ctx(struct signer *ctx)
+{
+	if (ctx->ecdsa_key)
+		EC_KEY_free(ctx->ecdsa_key);
+
+	if (ctx->evp_key)
+		EVP_PKEY_free(ctx->evp_key);
+
+	if (ctx->hash)
+		free(ctx->hash);
+}
+
+/*
+ * Convert an ECDSA signature to raw format
+ *
+ * openssl DER-encodes 'binary' signatures. We want the signature in a raw
+ * (R, S) point pair. So we have to dance a bit.
+ */
+static void ecdsa_sig_encode_raw(void *buf, const ECDSA_SIG *sig, size_t order)
+{
+	int point_bytes = order;
+	const BIGNUM *r, *s;
+	uintptr_t s_buf;
+
+	ECDSA_SIG_get0(sig, &r, &s);
+	s_buf = (uintptr_t)buf + point_bytes;
+	BN_bn2binpad(r, buf, point_bytes);
+	BN_bn2binpad(s, (void *)s_buf, point_bytes);
+}
+
+/* Get a signature from a raw encoding */
+static ECDSA_SIG *ecdsa_sig_from_raw(void *buf, size_t order)
+{
+	int point_bytes = order;
+	uintptr_t s_buf;
+	ECDSA_SIG *sig;
+	BIGNUM *r, *s;
+
+	sig = ECDSA_SIG_new();
+	if (!sig)
+		return NULL;
+
+	s_buf = (uintptr_t)buf + point_bytes;
+	r = BN_bin2bn(buf, point_bytes, NULL);
+	s = BN_bin2bn((void *)s_buf, point_bytes, NULL);
+	ECDSA_SIG_set0(sig, r, s);
+
+	return sig;
+}
+
+/* ECDSA key size in bytes */
+static size_t ecdsa_key_size_bytes(const EC_KEY *key)
+{
+	const EC_GROUP *group;
+
+	group = EC_KEY_get0_group(key);
+	return EC_GROUP_order_bits(group) / 8;
+}
+
+static int read_key(struct signer *ctx, const char *key_name)
+{
+	FILE *f = fopen(key_name, "r");
+
+	if (!f) {
+		fprintf(stderr, "Can not get key file '%s'\n", key_name);
+		return -ENOENT;
+	}
+
+	ctx->evp_key = PEM_read_PrivateKey(f, NULL, NULL, NULL);
+	fclose(f);
+	if (!ctx->evp_key) {
+		fprintf(stderr, "Can not read key from '%s'\n", key_name);
+		return -EIO;
+	}
+
+	if (EVP_PKEY_id(ctx->evp_key) != EVP_PKEY_EC) {
+		fprintf(stderr, "'%s' is not an ECDSA key\n", key_name);
+		return -EINVAL;
+	}
+
+	ctx->ecdsa_key = EVP_PKEY_get1_EC_KEY(ctx->evp_key);
+	if (!ctx->ecdsa_key)
+		fprintf(stderr, "Can not extract ECDSA key\n");
+
+	return (ctx->ecdsa_key) ? 0 : -EINVAL;
+}
+
+/* Prepare a 'signer' context that's ready to sign and verify. */
+static int prepare_ctx(struct signer *ctx, const struct image_sign_info *info)
+{
+	const char *kname = info->keydir;
+	int key_len_bytes, ret;
+
+	ret = alloc_ctx(ctx, info);
+	if (ret)
+		return ret;
+
+	ret = read_key(ctx, kname);
+	if (ret)
+		return ret;
+
+	key_len_bytes = ecdsa_key_size_bytes(ctx->ecdsa_key);
+	if (key_len_bytes != info->crypto->key_len) {
+		fprintf(stderr, "Expected a %u-bit key, got %u-bit key\n",
+			info->crypto->key_len * 8, key_len_bytes * 8);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int do_sign(struct signer *ctx, struct image_sign_info *info,
+		   const struct image_region region[], int region_count)
+{
+	const struct checksum_algo *algo = info->checksum;
+	ECDSA_SIG *sig;
+
+	algo->calculate(algo->name, region, region_count, ctx->hash);
+	sig = ECDSA_do_sign(ctx->hash, algo->checksum_len, ctx->ecdsa_key);
+
+	ecdsa_sig_encode_raw(ctx->signature, sig, info->crypto->key_len);
+
+	return 0;
+}
+
+static int ecdsa_check_signature(struct signer *ctx, struct image_sign_info *info)
+{
+	ECDSA_SIG *sig;
+	int okay;
+
+	sig = ecdsa_sig_from_raw(ctx->signature, info->crypto->key_len);
+	if (!sig)
+		return -ENOMEM;
+
+	okay = ECDSA_do_verify(ctx->hash, info->checksum->checksum_len,
+			       sig, ctx->ecdsa_key);
+	if (!okay)
+		fprintf(stderr, "WARNING: Signature is fake news!\n");
+
+	ECDSA_SIG_free(sig);
+	return !okay;
+}
+
+static int do_verify(struct signer *ctx, struct image_sign_info *info,
+		     const struct image_region region[], int region_count,
+		     uint8_t *raw_sig, uint sig_len)
+{
+	const struct checksum_algo *algo = info->checksum;
+
+	if (sig_len != info->crypto->key_len * 2) {
+		fprintf(stderr, "Signature has wrong length\n");
+		return -EINVAL;
+	}
+
+	memcpy(ctx->signature, raw_sig, sig_len);
+	algo->calculate(algo->name, region, region_count, ctx->hash);
+
+	return ecdsa_check_signature(ctx, info);
+}
+
+int ecdsa_sign(struct image_sign_info *info, const struct image_region region[],
+	       int region_count, uint8_t **sigp, uint *sig_len)
+{
+	struct signer ctx;
+	int ret;
+
+	ret = prepare_ctx(&ctx, info);
+	if (ret >= 0) {
+		do_sign(&ctx, info, region, region_count);
+		*sigp = ctx.signature;
+		*sig_len = info->crypto->key_len * 2;
+
+		ret = ecdsa_check_signature(&ctx, info);
+	}
+
+	free_ctx(&ctx);
+	return ret;
+}
+
+int ecdsa_verify(struct image_sign_info *info,
+		 const struct image_region region[], int region_count,
+		 uint8_t *sig, uint sig_len)
+{
+	struct signer ctx;
+	int ret;
+
+	ret = prepare_ctx(&ctx, info);
+	if (ret >= 0)
+		ret = do_verify(&ctx, info, region, region_count, sig, sig_len);
+
+	free_ctx(&ctx);
+	return ret;
+}
+
+static int do_add(struct signer *ctx, void *fdt, const char *key_node_name)
+{
+	int signature_node, key_node, ret, key_bits;
+	const char *curve_name;
+	const EC_GROUP *group;
+	const EC_POINT *point;
+	BIGNUM *x, *y;
+
+	signature_node = fdt_subnode_offset(fdt, 0, FIT_SIG_NODENAME);
+	if (signature_node < 0) {
+		fprintf(stderr, "Could not find 'signature node: %s\n",
+			fdt_strerror(signature_node));
+		return signature_node;
+	}
+
+	key_node = fdt_add_subnode(fdt, signature_node, key_node_name);
+	if (key_node < 0) {
+		fprintf(stderr, "Could not create '%s' node: %s\n",
+			key_node_name, fdt_strerror(key_node));
+		return key_node;
+	}
+
+	group = EC_KEY_get0_group(ctx->ecdsa_key);
+	key_bits = EC_GROUP_order_bits(group);
+	curve_name = OBJ_nid2sn(EC_GROUP_get_curve_name(group));
+	/* Let 'x' and 'y' memory leak by not BN_free()'ing them. */
+	x = BN_new();
+	y = BN_new();
+	point = EC_KEY_get0_public_key(ctx->ecdsa_key);
+	EC_POINT_get_affine_coordinates(group, point, x, y, NULL);
+
+	ret = fdt_setprop_string(fdt, key_node, "ecdsa,curve", curve_name);
+	if (ret < 0)
+		return ret;
+
+	ret = fdt_add_bignum(fdt, key_node, "ecdsa,x-point", x, key_bits);
+	if (ret < 0)
+		return ret;
+
+	ret = fdt_add_bignum(fdt, key_node, "ecdsa,y-point", y, key_bits);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+int ecdsa_add_verify_data(struct image_sign_info *info, void *fdt)
+{
+	const char *fdt_key_name;
+	struct signer ctx;
+	int ret;
+
+	fdt_key_name = info->keyname ? info->keyname : "default-key";
+	ret = prepare_ctx(&ctx, info);
+	if (ret >= 0)
+		do_add(&ctx, fdt, fdt_key_name);
+
+	free_ctx(&ctx);
+	return ret;
+}
diff --git a/tools/Makefile b/tools/Makefile
index 3b8e7ac73a..d020c55d66 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -70,6 +70,8 @@ RSA_OBJS-$(CONFIG_FIT_SIGNATURE) := $(addprefix lib/rsa/, \
 					rsa-sign.o rsa-verify.o \
 					rsa-mod-exp.o)
 
+ECDSA_OBJS-$(CONFIG_FIT_SIGNATURE) := $(addprefix lib/ecdsa/, ecdsa-libcrypto.o)
+
 AES_OBJS-$(CONFIG_FIT_CIPHER) := $(addprefix lib/aes/, \
 					aes-encrypt.o aes-decrypt.o)
 
@@ -124,6 +126,7 @@ dumpimage-mkimage-objs := aisimage.o \
 			gpimage.o \
 			gpimage-common.o \
 			mtk_image.o \
+			$(ECDSA_OBJS-y) \
 			$(RSA_OBJS-y) \
 			$(AES_OBJS-y)