[PATCH v4 3/6] lib: ecdsa: Implement signature verification for crypto_algo API

Alexandru Gagniuc
2021-04-15T20:05:06Z

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>
---
lib/ecdsa/ecdsa-verify.c | 117 ++++++++++++++++++++++++++++++++++++++-
1 file changed, 116 insertions(+), 1 deletion(-)

diff --git a/lib/ecdsa/ecdsa-verify.c b/lib/ecdsa/ecdsa-verify.c
index d2e6a40f4a..3e55b14497 100644
--- a/lib/ecdsa/ecdsa-verify.c
+++ b/lib/ecdsa/ecdsa-verify.c
@@ -1,13 +1,128 @@
// 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)
{
- return -EOPNOTSUPP;
+ 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);
}
+
+/*
+ * 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",
+};
--
2.26.3