/*
 * Copyright (c) 2013, Google Inc.
 *
 * SPDX-License-Identifier:     GPL-2.0+
 */

#ifndef USE_HOSTCC
#include <common.h>
#include <fdtdec.h>
#include <asm/types.h>
#include <asm/byteorder.h>
#include <linux/errno.h>
#include <asm/types.h>
#include <asm/unaligned.h>
#else
#include "fdt_host.h"
#include "mkimage.h"
#include <fdt_support.h>
#endif
#include <u-boot/rsa.h>
#include <u-boot/rsa-mod-exp.h>

#define UINT64_MULT32(v, multby)  (((uint64_t)(v)) * ((uint32_t)(multby)))

#define get_unaligned_be32(a) fdt32_to_cpu(*(uint32_t *)a)
#define put_unaligned_be32(a, b) (*(uint32_t *)(b) = cpu_to_fdt32(a))

/* Default public exponent for backward compatibility */
#define RSA_DEFAULT_PUBEXP      65537

/**
 * 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[])
{
        int i;

        for (i = (int)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);
}

/**
 * num_pub_exponent_bits() - Number of bits in the public exponent
 *
 * @key:        RSA key
 * @num_bits:   Storage for the number of public exponent bits
 */
static int num_public_exponent_bits(const struct rsa_public_key *key,
                int *num_bits)
{
        uint64_t exponent;
        int exponent_bits;
        const uint max_bits = (sizeof(exponent) * 8);

        exponent = key->exponent;
        exponent_bits = 0;

        if (!exponent) {
                *num_bits = exponent_bits;
                return 0;
        }

        for (exponent_bits = 1; exponent_bits < max_bits + 1; ++exponent_bits)
                if (!(exponent >>= 1)) {
                        *num_bits = exponent_bits;
                        return 0;
                }

        return -EINVAL;
}

/**
 * is_public_exponent_bit_set() - Check if a bit in the public exponent is set
 *
 * @key:        RSA key
 * @pos:        The bit position to check
 */
static int is_public_exponent_bit_set(const struct rsa_public_key *key,
                int pos)
{
        return key->exponent & (1ULL << pos);
}

/**
 * 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;
        int j, k;

        /* 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];
        uint32_t a_scaled[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);

        if (0 != num_public_exponent_bits(key, &k))
                return -EINVAL;

        if (k < 2) {
                debug("Public exponent is too short (%d bits, minimum 2)\n",
                      k);
                return -EINVAL;
        }

        if (!is_public_exponent_bit_set(key, 0)) {
                debug("LSB of RSA public exponent must be set.\n");
                return -EINVAL;
        }

        /* the bit at e[k-1] is 1 by definition, so start with: C := M */
        montgomery_mul(key, acc, val, key->rr); /* acc = a * RR / R mod n */
        /* retain scaled version for intermediate use */
        memcpy(a_scaled, acc, key->len * sizeof(a_scaled[0]));

        for (j = k - 2; j > 0; --j) {
                montgomery_mul(key, tmp, acc, acc); /* tmp = acc^2 / R mod n */

                if (is_public_exponent_bit_set(key, j)) {
                        /* acc = tmp * val / R mod n */
                        montgomery_mul(key, acc, tmp, a_scaled);
                } else {
                        /* e[j] == 0, copy tmp back to acc for next operation */
                        memcpy(acc, tmp, key->len * sizeof(acc[0]));
                }
        }

        /* the bit at e[0] is always 1 */
        montgomery_mul(key, tmp, acc, acc); /* tmp = acc^2 / R mod n */
        montgomery_mul(key, acc, tmp, val); /* acc = tmp * a / R mod M */
        memcpy(result, acc, key->len * sizeof(result[0]));

        /* 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 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]);
}

int rsa_mod_exp_sw(const uint8_t *sig, uint32_t sig_len,
                struct key_prop *prop, uint8_t *out)
{
        struct rsa_public_key key;
        int ret;

        if (!prop) {
                debug("%s: Skipping invalid prop", __func__);
                return -EBADF;
        }
        key.n0inv = prop->n0inv;
        key.len = prop->num_bits;

        if (!prop->public_exponent)
                key.exponent = RSA_DEFAULT_PUBEXP;
        else
                key.exponent =
                        fdt64_to_cpu(*((uint64_t *)(prop->public_exponent)));

        if (!key.len || !prop->modulus || !prop->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, (uint32_t *)prop->modulus, key.len);
        rsa_convert_big_endian(key.rr, (uint32_t *)prop->rr, key.len);
        if (!key.modulus || !key.rr) {
                debug("%s: Out of memory", __func__);
                return -ENOMEM;
        }

        uint32_t buf[sig_len / sizeof(uint32_t)];

        memcpy(buf, sig, sig_len);

        ret = pow_mod(&key, buf);
        if (ret)
                return ret;

        memcpy(out, buf, sig_len);

        return 0;
}