lib: ecdsa: Implement UCLASS_ECDSA verification on target

Implement the crypto_algo .verify() function for ecdsa256. Because
it backends on UCLASS_ECDSA, this change is focused on parsing the
keys from devicetree and passing this information to the specific
UCLASS driver.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>

lib/Kconfig

@@ -303,6 +303,7 @@ config AES
 	  supported by the algorithm but only a 128-bit key is supported at
 	  present.
 
+source lib/ecdsa/Kconfig
 source lib/rsa/Kconfig
 source lib/crypto/Kconfig
 source lib/crypt/Kconfig

lib/Makefile

@@ -60,6 +60,7 @@ endif
 
 obj-$(CONFIG_$(SPL_)ACPIGEN) += acpi/
 obj-$(CONFIG_$(SPL_)MD5) += md5.o
+obj-$(CONFIG_ECDSA) += ecdsa/
 obj-$(CONFIG_$(SPL_)RSA) += rsa/
 obj-$(CONFIG_HASH) += hash-checksum.o
 obj-$(CONFIG_SHA1) += sha1.o

lib/ecdsa/Kconfig

@@ -0,0 +1,23 @@
+config ECDSA
+	bool "Enable ECDSA support"
+	depends on DM
+	help
+	  This enables the ECDSA (elliptic curve signature) algorithm for FIT
+	  image verification in U-Boot. The ECDSA algorithm is implemented
+	  using the driver model, so CONFIG_DM is required by this library.
+	  See doc/uImage.FIT/signature.txt for more details.
+	  ECDSA is enabled for mkimage regardless of this option.
+
+if ECDSA
+
+config ECDSA_VERIFY
+	bool "Enable ECDSA verification support in U-Boot."
+	help
+	  Allow ECDSA signatures to be recognized and verified in U-Boot.
+
+config SPL_ECDSA_VERIFY
+	bool "Enable ECDSA verification support in SPL"
+	help
+	  Allow ECDSA signatures to be recognized and verified in SPL.
+
+endif

lib/ecdsa/Makefile

@@ -0,0 +1 @@
+obj-$(CONFIG_$(SPL_)ECDSA_VERIFY) += ecdsa-verify.o

lib/ecdsa/ecdsa-verify.c

@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * ECDSA signature verification for u-boot
+ *
+ * This implements the firmware-side wrapper for ECDSA verification. It bridges
+ * the struct crypto_algo API to the ECDSA uclass implementations.
+ *
+ * Copyright (c) 2020, Alexandru Gagniuc <mr.nuke.me@gmail.com>
+ */
+
+#include <crypto/ecdsa-uclass.h>
+#include <dm/uclass.h>
+#include <u-boot/ecdsa.h>
+
+/*
+ * Derive size of an ECDSA key from the curve name
+ *
+ * While it's possible to extract the key size by using string manipulation,
+ * use a list of known curves for the time being.
+ */
+static int ecdsa_key_size(const char *curve_name)
+{
+	if (!strcmp(curve_name, "prime256v1"))
+		return 256;
+	else
+		return 0;
+}
+
+static int fdt_get_key(struct ecdsa_public_key *key, const void *fdt, int node)
+{
+	int x_len, y_len;
+
+	key->curve_name = fdt_getprop(fdt, node, "ecdsa,curve", NULL);
+	key->size_bits = ecdsa_key_size(key->curve_name);
+	if (key->size_bits == 0) {
+		debug("Unknown ECDSA curve '%s'", key->curve_name);
+		return -EINVAL;
+	}
+
+	key->x = fdt_getprop(fdt, node, "ecdsa,x-point", &x_len);
+	key->y = fdt_getprop(fdt, node, "ecdsa,y-point", &y_len);
+
+	if (!key->x || !key->y)
+		return -EINVAL;
+
+	if (x_len != (key->size_bits / 8) || y_len != (key->size_bits / 8)) {
+		printf("%s: node=%d, curve@%p x@%p+%i y@%p+%i\n", __func__,
+		       node, key->curve_name, key->x, x_len, key->y, y_len);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int ecdsa_verify_hash(struct udevice *dev,
+			     const struct image_sign_info *info,
+			     const void *hash, const void *sig, uint sig_len)
+{
+	const struct ecdsa_ops *ops = device_get_ops(dev);
+	const struct checksum_algo *algo = info->checksum;
+	struct ecdsa_public_key key;
+	int sig_node, key_node, ret;
+
+	if (!ops || !ops->verify)
+		return -ENODEV;
+
+	if (info->required_keynode > 0) {
+		ret = fdt_get_key(&key, info->fdt_blob, info->required_keynode);
+		if (ret < 0)
+			return ret;
+
+		return ops->verify(dev, &key, hash, algo->checksum_len,
+				   sig, sig_len);
+	}
+
+	sig_node = fdt_subnode_offset(info->fdt_blob, 0, FIT_SIG_NODENAME);
+	if (sig_node < 0)
+		return -ENOENT;
+
+	/* Try all possible keys under the "/signature" node */
+	fdt_for_each_subnode(key_node, info->fdt_blob, sig_node) {
+		ret = fdt_get_key(&key, info->fdt_blob, key_node);
+		if (ret < 0)
+			continue;
+
+		ret = ops->verify(dev, &key, hash, algo->checksum_len,
+				  sig, sig_len);
+
+		/* On success, don't worry about remaining keys */
+		if (!ret)
+			return 0;
+	}
+
+	return -EPERM;
+}
+
+int ecdsa_verify(struct image_sign_info *info,
+		 const struct image_region region[], int region_count,
+		 uint8_t *sig, uint sig_len)
+{
+	const struct checksum_algo *algo = info->checksum;
+	uint8_t hash[algo->checksum_len];
+	struct udevice *dev;
+	int ret;
+
+	ret = uclass_first_device_err(UCLASS_ECDSA, &dev);
+	if (ret) {
+		debug("ECDSA: Could not find ECDSA implementation: %d\n", ret);
+		return ret;
+	}
+
+	ret = algo->calculate(algo->name, region, region_count, hash);
+	if (ret < 0)
+		return -EINVAL;
+
+	return ecdsa_verify_hash(dev, info, hash, sig, sig_len);
+}
+
+U_BOOT_CRYPTO_ALGO(ecdsa) = {
+	.name = "ecdsa256",
+	.key_len = ECDSA256_BYTES,
+	.verify = ecdsa_verify,
+};
+
+/*
+ * uclass definition for ECDSA API
+ *
+ * We don't implement any wrappers around ecdsa_ops->verify() because it's
+ * trivial to call ops->verify().
+ */
+UCLASS_DRIVER(ecdsa) = {
+	.id		= UCLASS_ECDSA,
+	.name		= "ecdsa_verifier",
+};