lib/rsa: Make fdt_add_bignum() available outside of RSA code

fdt_add_bignum() is useful for algorithms other than just RSA. To
allow its use for ECDSA, move it to a common file under lib/.

The new file is suffixed with '-libcrypto' because it has a direct
dependency on openssl. This is due to the use of the "BIGNUM *" type.

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

include/u-boot/fdt-libcrypto.h

@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (c) 2020, Alexandru Gagniuc <mr.nuke.me@gmail.com>
+ * Copyright (c) 2013, Google Inc.
+ */
+
+#ifndef _FDT_LIBCRYPTO_H
+#define _FDT_LIBCRYPTO_H
+
+#include <openssl/bn.h>
+
+/**
+ * fdt_add_bignum() - Write a libcrypto BIGNUM as an FDT property
+ *
+ * Convert a libcrypto BIGNUM * into a big endian array of integers.
+ *
+ * @blob:	FDT blob to modify
+ * @noffset:	Offset of the FDT node
+ * @prop_name:	What to call the property in the FDT
+ * @num:	pointer to a libcrypto big number
+ * @num_bits:	How big is 'num' in bits?
+ * @return 0 if all good all working, -ve on horror
+ */
+int fdt_add_bignum(void *blob, int noffset, const char *prop_name,
+		   BIGNUM *num, int num_bits);
+
+#endif /* _FDT_LIBCRYPTO_H */

lib/fdt-libcrypto.c

@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2020, Alexandru Gagniuc <mr.nuke.me@gmail.com>
+ * Copyright (c) 2013, Google Inc.
+ */
+
+#include <libfdt.h>
+#include <u-boot/fdt-libcrypto.h>
+
+int fdt_add_bignum(void *blob, int noffset, const char *prop_name,
+		   BIGNUM *num, int num_bits)
+{
+	int nwords = num_bits / 32;
+	int size;
+	uint32_t *buf, *ptr;
+	BIGNUM *tmp, *big2, *big32, *big2_32;
+	BN_CTX *ctx;
+	int ret;
+
+	tmp = BN_new();
+	big2 = BN_new();
+	big32 = BN_new();
+	big2_32 = BN_new();
+
+	/*
+	 * Note: This code assumes that all of the above succeed, or all fail.
+	 * In practice memory allocations generally do not fail (unless the
+	 * process is killed), so it does not seem worth handling each of these
+	 * as a separate case. Technicaly this could leak memory on failure,
+	 * but a) it won't happen in practice, and b) it doesn't matter as we
+	 * will immediately exit with a failure code.
+	 */
+	if (!tmp || !big2 || !big32 || !big2_32) {
+		fprintf(stderr, "Out of memory (bignum)\n");
+		return -ENOMEM;
+	}
+	ctx = BN_CTX_new();
+	if (!ctx) {
+		fprintf(stderr, "Out of memory (bignum context)\n");
+		return -ENOMEM;
+	}
+	BN_set_word(big2, 2L);
+	BN_set_word(big32, 32L);
+	BN_exp(big2_32, big2, big32, ctx); /* B = 2^32 */
+
+	size = nwords * sizeof(uint32_t);
+	buf = malloc(size);
+	if (!buf) {
+		fprintf(stderr, "Out of memory (%d bytes)\n", size);
+		return -ENOMEM;
+	}
+
+	/* Write out modulus as big endian array of integers */
+	for (ptr = buf + nwords - 1; ptr >= buf; ptr--) {
+		BN_mod(tmp, num, big2_32, ctx); /* n = N mod B */
+		*ptr = cpu_to_fdt32(BN_get_word(tmp));
+		BN_rshift(num, num, 32); /*  N = N/B */
+	}
+
+	/*
+	 * We try signing with successively increasing size values, so this
+	 * might fail several times
+	 */
+	ret = fdt_setprop(blob, noffset, prop_name, buf, size);
+	free(buf);
+	BN_free(tmp);
+	BN_free(big2);
+	BN_free(big32);
+	BN_free(big2_32);
+
+	return ret ? -FDT_ERR_NOSPACE : 0;
+}

lib/rsa/rsa-sign.c

@@ -9,6 +9,7 @@
 #include <string.h>
 #include <image.h>
 #include <time.h>
+#include <u-boot/fdt-libcrypto.h>
 #include <openssl/bn.h>
 #include <openssl/rsa.h>
 #include <openssl/pem.h>
@@ -680,70 +681,6 @@ int rsa_get_params(RSA *key, uint64_t *exponent, uint32_t *n0_invp,
 	return ret;
 }
 
-static int fdt_add_bignum(void *blob, int noffset, const char *prop_name,
-			  BIGNUM *num, int num_bits)
-{
-	int nwords = num_bits / 32;
-	int size;
-	uint32_t *buf, *ptr;
-	BIGNUM *tmp, *big2, *big32, *big2_32;
-	BN_CTX *ctx;
-	int ret;
-
-	tmp = BN_new();
-	big2 = BN_new();
-	big32 = BN_new();
-	big2_32 = BN_new();
-
-	/*
-	 * Note: This code assumes that all of the above succeed, or all fail.
-	 * In practice memory allocations generally do not fail (unless the
-	 * process is killed), so it does not seem worth handling each of these
-	 * as a separate case. Technicaly this could leak memory on failure,
-	 * but a) it won't happen in practice, and b) it doesn't matter as we
-	 * will immediately exit with a failure code.
-	 */
-	if (!tmp || !big2 || !big32 || !big2_32) {
-		fprintf(stderr, "Out of memory (bignum)\n");
-		return -ENOMEM;
-	}
-	ctx = BN_CTX_new();
-	if (!ctx) {
-		fprintf(stderr, "Out of memory (bignum context)\n");
-		return -ENOMEM;
-	}
-	BN_set_word(big2, 2L);
-	BN_set_word(big32, 32L);
-	BN_exp(big2_32, big2, big32, ctx); /* B = 2^32 */
-
-	size = nwords * sizeof(uint32_t);
-	buf = malloc(size);
-	if (!buf) {
-		fprintf(stderr, "Out of memory (%d bytes)\n", size);
-		return -ENOMEM;
-	}
-
-	/* Write out modulus as big endian array of integers */
-	for (ptr = buf + nwords - 1; ptr >= buf; ptr--) {
-		BN_mod(tmp, num, big2_32, ctx); /* n = N mod B */
-		*ptr = cpu_to_fdt32(BN_get_word(tmp));
-		BN_rshift(num, num, 32); /*  N = N/B */
-	}
-
-	/*
-	 * We try signing with successively increasing size values, so this
-	 * might fail several times
-	 */
-	ret = fdt_setprop(blob, noffset, prop_name, buf, size);
-	free(buf);
-	BN_free(tmp);
-	BN_free(big2);
-	BN_free(big32);
-	BN_free(big2_32);
-
-	return ret ? -FDT_ERR_NOSPACE : 0;
-}
-
 int rsa_add_verify_data(struct image_sign_info *info, void *keydest)
 {
 	BIGNUM *modulus, *r_squared;

tools/Makefile

@@ -73,6 +73,10 @@ RSA_OBJS-$(CONFIG_FIT_SIGNATURE) := $(addprefix lib/rsa/, \
 AES_OBJS-$(CONFIG_FIT_CIPHER) := $(addprefix lib/aes/, \
 					aes-encrypt.o aes-decrypt.o)
 
+# Cryptographic helpers that depend on openssl/libcrypto
+LIBCRYPTO_OBJS-$(CONFIG_FIT_SIGNATURE) := $(addprefix lib/, \
+					fdt-libcrypto.o)
+
 ROCKCHIP_OBS = lib/rc4.o rkcommon.o rkimage.o rksd.o rkspi.o
 
 # common objs for dumpimage and mkimage
@@ -115,6 +119,7 @@ dumpimage-mkimage-objs := aisimage.o \
 			zynqimage.o \
 			zynqmpimage.o \
 			zynqmpbif.o \
+			$(LIBCRYPTO_OBJS-y) \
 			$(LIBFDT_OBJS) \
 			gpimage.o \
 			gpimage-common.o \