// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright 2024- IBM Corp.
 *
 * X25519 scalar multiplication with 51 bits limbs for PPC64le.
 *   Based on RFC7748 and AArch64 optimized implementation for X25519
 *     - Algorithm 1 Scalar multiplication of a variable point
 */

#include <linux/types.h>
#include <linux/jump_label.h>
#include <linux/kernel.h>

#include <linux/cpufeature.h>
#include <linux/processor.h>

typedef uint64_t fe51[5];

asmlinkage void x25519_fe51_mul(fe51 h, const fe51 f, const fe51 g);
asmlinkage void x25519_fe51_sqr(fe51 h, const fe51 f);
asmlinkage void x25519_fe51_mul121666(fe51 h, fe51 f);
asmlinkage void x25519_fe51_sqr_times(fe51 h, const fe51 f, int n);
asmlinkage void x25519_fe51_frombytes(fe51 h, const uint8_t *s);
asmlinkage void x25519_fe51_tobytes(uint8_t *s, const fe51 h);
asmlinkage void x25519_cswap(fe51 p, fe51 q, unsigned int bit);

#define fmul x25519_fe51_mul
#define fsqr x25519_fe51_sqr
#define fmul121666 x25519_fe51_mul121666
#define fe51_tobytes x25519_fe51_tobytes

static void fadd(fe51 h, const fe51 f, const fe51 g)
{
        h[0] = f[0] + g[0];
        h[1] = f[1] + g[1];
        h[2] = f[2] + g[2];
        h[3] = f[3] + g[3];
        h[4] = f[4] + g[4];
}

/*
 * Prime = 2 ** 255 - 19, 255 bits
 *    (0x7fffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffed)
 *
 * Prime in 5 51-bit limbs
 */
static fe51 prime51 = { 0x7ffffffffffed, 0x7ffffffffffff, 0x7ffffffffffff, 0x7ffffffffffff, 0x7ffffffffffff};

static void fsub(fe51 h, const fe51 f, const fe51 g)
{
        h[0] = (f[0] + ((prime51[0] * 2))) - g[0];
        h[1] = (f[1] + ((prime51[1] * 2))) - g[1];
        h[2] = (f[2] + ((prime51[2] * 2))) - g[2];
        h[3] = (f[3] + ((prime51[3] * 2))) - g[3];
        h[4] = (f[4] + ((prime51[4] * 2))) - g[4];
}

static void fe51_frombytes(fe51 h, const uint8_t *s)
{
        /*
         * Make sure 64-bit aligned.
         */
        unsigned char sbuf[32+8];
        unsigned char *sb = PTR_ALIGN((void *)sbuf, 8);

        memcpy(sb, s, 32);
        x25519_fe51_frombytes(h, sb);
}

static void finv(fe51 o, const fe51 i)
{
        fe51 a0, b, c, t00;

        fsqr(a0, i);
        x25519_fe51_sqr_times(t00, a0, 2);

        fmul(b, t00, i);
        fmul(a0, b, a0);

        fsqr(t00, a0);

        fmul(b, t00, b);
        x25519_fe51_sqr_times(t00, b, 5);

        fmul(b, t00, b);
        x25519_fe51_sqr_times(t00, b, 10);

        fmul(c, t00, b);
        x25519_fe51_sqr_times(t00, c, 20);

        fmul(t00, t00, c);
        x25519_fe51_sqr_times(t00, t00, 10);

        fmul(b, t00, b);
        x25519_fe51_sqr_times(t00, b, 50);

        fmul(c, t00, b);
        x25519_fe51_sqr_times(t00, c, 100);

        fmul(t00, t00, c);
        x25519_fe51_sqr_times(t00, t00, 50);

        fmul(t00, t00, b);
        x25519_fe51_sqr_times(t00, t00, 5);

        fmul(o, t00, a0);
}

static void curve25519_fe51(uint8_t out[32], const uint8_t scalar[32],
                            const uint8_t point[32])
{
        fe51 x1, x2, z2, x3, z3;
        uint8_t s[32];
        unsigned int swap = 0;
        int i;

        memcpy(s, scalar, 32);
        s[0]  &= 0xf8;
        s[31] &= 0x7f;
        s[31] |= 0x40;
        fe51_frombytes(x1, point);

        z2[0] = z2[1] = z2[2] = z2[3] = z2[4] = 0;
        x3[0] = x1[0];
        x3[1] = x1[1];
        x3[2] = x1[2];
        x3[3] = x1[3];
        x3[4] = x1[4];

        x2[0] = z3[0] = 1;
        x2[1] = z3[1] = 0;
        x2[2] = z3[2] = 0;
        x2[3] = z3[3] = 0;
        x2[4] = z3[4] = 0;

        for (i = 254; i >= 0; --i) {
                unsigned int k_t = 1 & (s[i / 8] >> (i & 7));
                fe51 a, b, c, d, e;
                fe51 da, cb, aa, bb;
                fe51 dacb_p, dacb_m;

                swap ^= k_t;
                x25519_cswap(x2, x3, swap);
                x25519_cswap(z2, z3, swap);
                swap = k_t;

                fsub(b, x2, z2);                // B = x_2 - z_2
                fadd(a, x2, z2);                // A = x_2 + z_2
                fsub(d, x3, z3);                // D = x_3 - z_3
                fadd(c, x3, z3);                // C = x_3 + z_3

                fsqr(bb, b);                    // BB = B^2
                fsqr(aa, a);                    // AA = A^2
                fmul(da, d, a);                 // DA = D * A
                fmul(cb, c, b);                 // CB = C * B

                fsub(e, aa, bb);                // E = AA - BB
                fmul(x2, aa, bb);               // x2 = AA * BB
                fadd(dacb_p, da, cb);           // DA + CB
                fsub(dacb_m, da, cb);           // DA - CB

                fmul121666(z3, e);              // 121666 * E
                fsqr(z2, dacb_m);               // (DA - CB)^2
                fsqr(x3, dacb_p);               // x3 = (DA + CB)^2
                fadd(b, bb, z3);                // BB + 121666 * E
                fmul(z3, x1, z2);               // z3 = x1 * (DA - CB)^2
                fmul(z2, e, b);         // z2 = e * (BB + (DA + CB)^2)
        }

        finv(z2, z2);
        fmul(x2, x2, z2);
        fe51_tobytes(out, x2);
}

static void curve25519_arch(u8 mypublic[CURVE25519_KEY_SIZE],
                            const u8 secret[CURVE25519_KEY_SIZE],
                            const u8 basepoint[CURVE25519_KEY_SIZE])
{
        curve25519_fe51(mypublic, secret, basepoint);
}

static void curve25519_base_arch(u8 pub[CURVE25519_KEY_SIZE],
                                 const u8 secret[CURVE25519_KEY_SIZE])
{
        curve25519_fe51(pub, secret, curve25519_base_point);
}