Re: [PATCH v3 13/19] crypto: Add generic 64-bit carry-less multiply routine

[Ard Biesheuvel <ardb@kernel.org>]

On Mon, 21 Aug 2023 at 18:19, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>

> ---
>  host/include/generic/host/crypto/clmul.h | 15 +++++++++++++++
>  include/crypto/clmul.h                   | 19 +++++++++++++++++++
>  crypto/clmul.c                           | 18 ++++++++++++++++++
>  3 files changed, 52 insertions(+)
>  create mode 100644 host/include/generic/host/crypto/clmul.h
>
> diff --git a/host/include/generic/host/crypto/clmul.h b/host/include/generic/host/crypto/clmul.h
> new file mode 100644
> index 0000000000..915bfb88d3
> --- /dev/null
> +++ b/host/include/generic/host/crypto/clmul.h
> @@ -0,0 +1,15 @@
> +/*
> + * No host specific carry-less multiply acceleration.
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#ifndef GENERIC_HOST_CRYPTO_CLMUL_H
> +#define GENERIC_HOST_CRYPTO_CLMUL_H
> +
> +#define HAVE_CLMUL_ACCEL  false
> +#define ATTR_CLMUL_ACCEL
> +
> +Int128 clmul_64_accel(uint64_t, uint64_t)
> +    QEMU_ERROR("unsupported accel");
> +
> +#endif /* GENERIC_HOST_CRYPTO_CLMUL_H */
> diff --git a/include/crypto/clmul.h b/include/crypto/clmul.h
> index 0ea25a252c..c82d2d7559 100644
> --- a/include/crypto/clmul.h
> +++ b/include/crypto/clmul.h
> @@ -8,6 +8,9 @@
>  #ifndef CRYPTO_CLMUL_H
>  #define CRYPTO_CLMUL_H
>
> +#include "qemu/int128.h"
> +#include "host/crypto/clmul.h"
> +
>  /**
>   * clmul_8x8_low:
>   *
> @@ -61,4 +64,20 @@ uint64_t clmul_16x2_odd(uint64_t, uint64_t);
>   */
>  uint64_t clmul_32(uint32_t, uint32_t);
>
> +/**
> + * clmul_64:
> + *
> + * Perform a 64x64->128 carry-less multiply.
> + */
> +Int128 clmul_64_gen(uint64_t, uint64_t);
> +
> +static inline Int128 clmul_64(uint64_t a, uint64_t b)
> +{
> +    if (HAVE_CLMUL_ACCEL) {
> +        return clmul_64_accel(a, b);
> +    } else {
> +        return clmul_64_gen(a, b);
> +    }
> +}
> +
>  #endif /* CRYPTO_CLMUL_H */
> diff --git a/crypto/clmul.c b/crypto/clmul.c
> index 36ada1be9d..abf79cc49a 100644
> --- a/crypto/clmul.c
> +++ b/crypto/clmul.c
> @@ -92,3 +92,21 @@ uint64_t clmul_32(uint32_t n, uint32_t m32)
>      }
>      return r;
>  }
> +
> +Int128 clmul_64_gen(uint64_t n, uint64_t m)
> +{
> +    uint64_t rl = 0, rh = 0;
> +
> +    /* Bit 0 can only influence the low 64-bit result.  */
> +    if (n & 1) {
> +        rl = m;
> +    }
> +
> +    for (int i = 1; i < 64; ++i) {
> +        uint64_t mask = -(n & 1);
> +        rl ^= (m << i) & mask;
> +        rh ^= (m >> (64 - i)) & mask;
> +        n >>= 1;
> +    }
> +    return int128_make128(rl, rh);
> +}
> --
> 2.34.1
>