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  • /*
     * Copyright (c) 2013, Google Inc.
     *
    
     * SPDX-License-Identifier:	GPL-2.0+
    
     */
    
    #include <common.h>
    #include <fdtdec.h>
    #include <rsa.h>
    #include <sha1.h>
    
    #include <sha256.h>
    
    #include <asm/byteorder.h>
    #include <asm/errno.h>
    #include <asm/unaligned.h>
    
    #define UINT64_MULT32(v, multby)  (((uint64_t)(v)) * ((uint32_t)(multby)))
    
    /**
     * subtract_modulus() - subtract modulus from the given value
     *
     * @key:	Key containing modulus to subtract
     * @num:	Number to subtract modulus from, as little endian word array
     */
    static void subtract_modulus(const struct rsa_public_key *key, uint32_t num[])
    {
    	int64_t acc = 0;
    	uint i;
    
    	for (i = 0; i < key->len; i++) {
    		acc += (uint64_t)num[i] - key->modulus[i];
    		num[i] = (uint32_t)acc;
    		acc >>= 32;
    	}
    }
    
    /**
     * greater_equal_modulus() - check if a value is >= modulus
     *
     * @key:	Key containing modulus to check
     * @num:	Number to check against modulus, as little endian word array
     * @return 0 if num < modulus, 1 if num >= modulus
     */
    static int greater_equal_modulus(const struct rsa_public_key *key,
    				 uint32_t num[])
    {
    	uint32_t i;
    
    	for (i = key->len - 1; i >= 0; i--) {
    		if (num[i] < key->modulus[i])
    			return 0;
    		if (num[i] > key->modulus[i])
    			return 1;
    	}
    
    	return 1;  /* equal */
    }
    
    /**
     * montgomery_mul_add_step() - Perform montgomery multiply-add step
     *
     * Operation: montgomery result[] += a * b[] / n0inv % modulus
     *
     * @key:	RSA key
     * @result:	Place to put result, as little endian word array
     * @a:		Multiplier
     * @b:		Multiplicand, as little endian word array
     */
    static void montgomery_mul_add_step(const struct rsa_public_key *key,
    		uint32_t result[], const uint32_t a, const uint32_t b[])
    {
    	uint64_t acc_a, acc_b;
    	uint32_t d0;
    	uint i;
    
    	acc_a = (uint64_t)a * b[0] + result[0];
    	d0 = (uint32_t)acc_a * key->n0inv;
    	acc_b = (uint64_t)d0 * key->modulus[0] + (uint32_t)acc_a;
    	for (i = 1; i < key->len; i++) {
    		acc_a = (acc_a >> 32) + (uint64_t)a * b[i] + result[i];
    		acc_b = (acc_b >> 32) + (uint64_t)d0 * key->modulus[i] +
    				(uint32_t)acc_a;
    		result[i - 1] = (uint32_t)acc_b;
    	}
    
    	acc_a = (acc_a >> 32) + (acc_b >> 32);
    
    	result[i - 1] = (uint32_t)acc_a;
    
    	if (acc_a >> 32)
    		subtract_modulus(key, result);
    }
    
    /**
     * montgomery_mul() - Perform montgomery mutitply
     *
     * Operation: montgomery result[] = a[] * b[] / n0inv % modulus
     *
     * @key:	RSA key
     * @result:	Place to put result, as little endian word array
     * @a:		Multiplier, as little endian word array
     * @b:		Multiplicand, as little endian word array
     */
    static void montgomery_mul(const struct rsa_public_key *key,
    		uint32_t result[], uint32_t a[], const uint32_t b[])
    {
    	uint i;
    
    	for (i = 0; i < key->len; ++i)
    		result[i] = 0;
    	for (i = 0; i < key->len; ++i)
    		montgomery_mul_add_step(key, result, a[i], b);
    }
    
    /**
     * pow_mod() - in-place public exponentiation
     *
     * @key:	RSA key
     * @inout:	Big-endian word array containing value and result
     */
    static int pow_mod(const struct rsa_public_key *key, uint32_t *inout)
    {
    	uint32_t *result, *ptr;
    	uint i;
    
    	/* Sanity check for stack size - key->len is in 32-bit words */
    	if (key->len > RSA_MAX_KEY_BITS / 32) {
    		debug("RSA key words %u exceeds maximum %d\n", key->len,
    		      RSA_MAX_KEY_BITS / 32);
    		return -EINVAL;
    	}
    
    	uint32_t val[key->len], acc[key->len], tmp[key->len];
    	result = tmp;  /* Re-use location. */
    
    	/* Convert from big endian byte array to little endian word array. */
    	for (i = 0, ptr = inout + key->len - 1; i < key->len; i++, ptr--)
    		val[i] = get_unaligned_be32(ptr);
    
    	montgomery_mul(key, acc, val, key->rr);  /* axx = a * RR / R mod M */
    	for (i = 0; i < 16; i += 2) {
    		montgomery_mul(key, tmp, acc, acc); /* tmp = acc^2 / R mod M */
    		montgomery_mul(key, acc, tmp, tmp); /* acc = tmp^2 / R mod M */
    	}
    	montgomery_mul(key, result, acc, val);  /* result = XX * a / R mod M */
    
    	/* Make sure result < mod; result is at most 1x mod too large. */
    	if (greater_equal_modulus(key, result))
    		subtract_modulus(key, result);
    
    	/* Convert to bigendian byte array */
    	for (i = key->len - 1, ptr = inout; (int)i >= 0; i--, ptr++)
    		put_unaligned_be32(result[i], ptr);
    
    	return 0;
    }
    
    static int rsa_verify_key(const struct rsa_public_key *key, const uint8_t *sig,
    
    			  const uint32_t sig_len, const uint8_t *hash,
    			  struct checksum_algo *algo)
    
    {
    	const uint8_t *padding;
    	int pad_len;
    	int ret;
    
    
    	if (!key || !sig || !hash || !algo)
    
    		return -EIO;
    
    	if (sig_len != (key->len * sizeof(uint32_t))) {
    		debug("Signature is of incorrect length %d\n", sig_len);
    		return -EINVAL;
    	}
    
    
    	debug("Checksum algorithm: %s", algo->name);
    
    
    	/* Sanity check for stack size */
    	if (sig_len > RSA_MAX_SIG_BITS / 8) {
    		debug("Signature length %u exceeds maximum %d\n", sig_len,
    		      RSA_MAX_SIG_BITS / 8);
    		return -EINVAL;
    	}
    
    	uint32_t buf[sig_len / sizeof(uint32_t)];
    
    	memcpy(buf, sig, sig_len);
    
    	ret = pow_mod(key, buf);
    	if (ret)
    		return ret;
    
    
    	padding = algo->rsa_padding;
    
    	pad_len = algo->pad_len - algo->checksum_len;
    
    
    	/* Check pkcs1.5 padding bytes. */
    	if (memcmp(buf, padding, pad_len)) {
    		debug("In RSAVerify(): Padding check failed!\n");
    		return -EINVAL;
    	}
    
    	/* Check hash. */
    	if (memcmp((uint8_t *)buf + pad_len, hash, sig_len - pad_len)) {
    		debug("In RSAVerify(): Hash check failed!\n");
    		return -EACCES;
    	}
    
    	return 0;
    }
    
    static void rsa_convert_big_endian(uint32_t *dst, const uint32_t *src, int len)
    {
    	int i;
    
    	for (i = 0; i < len; i++)
    		dst[i] = fdt32_to_cpu(src[len - 1 - i]);
    }
    
    static int rsa_verify_with_keynode(struct image_sign_info *info,
    		const void *hash, uint8_t *sig, uint sig_len, int node)
    {
    	const void *blob = info->fdt_blob;
    	struct rsa_public_key key;
    	const void *modulus, *rr;
    	int ret;
    
    	if (node < 0) {
    		debug("%s: Skipping invalid node", __func__);
    		return -EBADF;
    	}
    	if (!fdt_getprop(blob, node, "rsa,n0-inverse", NULL)) {
    		debug("%s: Missing rsa,n0-inverse", __func__);
    		return -EFAULT;
    	}
    	key.len = fdtdec_get_int(blob, node, "rsa,num-bits", 0);
    	key.n0inv = fdtdec_get_int(blob, node, "rsa,n0-inverse", 0);
    	modulus = fdt_getprop(blob, node, "rsa,modulus", NULL);
    	rr = fdt_getprop(blob, node, "rsa,r-squared", NULL);
    	if (!key.len || !modulus || !rr) {
    		debug("%s: Missing RSA key info", __func__);
    		return -EFAULT;
    	}
    
    	/* Sanity check for stack size */
    	if (key.len > RSA_MAX_KEY_BITS || key.len < RSA_MIN_KEY_BITS) {
    		debug("RSA key bits %u outside allowed range %d..%d\n",
    		      key.len, RSA_MIN_KEY_BITS, RSA_MAX_KEY_BITS);
    		return -EFAULT;
    	}
    	key.len /= sizeof(uint32_t) * 8;
    	uint32_t key1[key.len], key2[key.len];
    
    	key.modulus = key1;
    	key.rr = key2;
    	rsa_convert_big_endian(key.modulus, modulus, key.len);
    	rsa_convert_big_endian(key.rr, rr, key.len);
    	if (!key.modulus || !key.rr) {
    		debug("%s: Out of memory", __func__);
    		return -ENOMEM;
    	}
    
    	debug("key length %d\n", key.len);
    
    	ret = rsa_verify_key(&key, sig, sig_len, hash, info->algo->checksum);
    
    	if (ret) {
    		printf("%s: RSA failed to verify: %d\n", __func__, ret);
    		return ret;
    	}
    
    	return 0;
    }
    
    int rsa_verify(struct image_sign_info *info,
    	       const struct image_region region[], int region_count,
    	       uint8_t *sig, uint sig_len)
    {
    	const void *blob = info->fdt_blob;
    
    	/* Reserve memory for maximum checksum-length */
    
    	uint8_t hash[info->algo->checksum->pad_len];
    
    	int ndepth, noffset;
    	int sig_node, node;
    	char name[100];
    
    	int ret;
    
    	/*
    	 * Verify that the checksum-length does not exceed the
    	 * rsa-signature-length
    	 */
    
    	if (info->algo->checksum->checksum_len >
    	    info->algo->checksum->pad_len) {
    		debug("%s: invlaid checksum-algorithm %s for %s\n",
    		      __func__, info->algo->checksum->name, info->algo->name);
    
    		return -EINVAL;
    	}
    
    
    	sig_node = fdt_subnode_offset(blob, 0, FIT_SIG_NODENAME);
    	if (sig_node < 0) {
    		debug("%s: No signature node found\n", __func__);
    		return -ENOENT;
    	}
    
    
    	/* Calculate checksum with checksum-algorithm */
    	info->algo->checksum->calculate(region, region_count, hash);
    
    
    	/* See if we must use a particular key */
    	if (info->required_keynode != -1) {
    		ret = rsa_verify_with_keynode(info, hash, sig, sig_len,
    			info->required_keynode);
    		if (!ret)
    			return ret;
    	}
    
    	/* Look for a key that matches our hint */
    	snprintf(name, sizeof(name), "key-%s", info->keyname);
    	node = fdt_subnode_offset(blob, sig_node, name);
    	ret = rsa_verify_with_keynode(info, hash, sig, sig_len, node);
    	if (!ret)
    		return ret;
    
    	/* No luck, so try each of the keys in turn */
    	for (ndepth = 0, noffset = fdt_next_node(info->fit, sig_node, &ndepth);
    			(noffset >= 0) && (ndepth > 0);
    			noffset = fdt_next_node(info->fit, noffset, &ndepth)) {
    		if (ndepth == 1 && noffset != node) {
    			ret = rsa_verify_with_keynode(info, hash, sig, sig_len,
    						      noffset);
    			if (!ret)
    				break;
    		}
    	}
    
    	return ret;
    }