Re: [PATCH 2/2] target/arm: Implement an IMPDEF pauth algorithm

["Alex Bennée" <alex.bennee@linaro.org>]

Richard Henderson <richard.henderson@linaro.org> writes:

> Without hardware acceleration, a cryptographically strong
> algorithm is too expensive for pauth_computepac.
>
> Even with hardware accel, we are not currently expecting
> to link the linux-user binaries to any crypto libraries,
> and doing so would generally make the --static build fail.
>
> So choose XXH64 as a reasonably quick and decent hash.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  target/arm/pauth_helper.c | 75 ++++++++++++++++++++++++++++++++++++---
>  1 file changed, 70 insertions(+), 5 deletions(-)
>
> diff --git a/target/arm/pauth_helper.c b/target/arm/pauth_helper.c
> index 6dbab03768..f1a4389465 100644
> --- a/target/arm/pauth_helper.c
> +++ b/target/arm/pauth_helper.c
> @@ -207,8 +207,8 @@ static uint64_t tweak_inv_shuffle(uint64_t i)
>      return o;
>  }
>  
> -static uint64_t pauth_computepac(uint64_t data, uint64_t modifier,
> -                                 ARMPACKey key)
> +static uint64_t __attribute__((noinline))
> +pauth_computepac_architected(uint64_t data, uint64_t modifier, ARMPACKey key)
>  {
>      static const uint64_t RC[5] = {
>          0x0000000000000000ull,
> @@ -272,6 +272,71 @@ static uint64_t pauth_computepac(uint64_t data, uint64_t modifier,
>      return workingval;
>  }
>  
> +/*
> + * The XXH64 algorithm from
> + * https://github.com/Cyan4973/xxHash/blob/v0.8.0/xxhash.h
> + */
> +#define PRIME64_1   0x9E3779B185EBCA87ULL
> +#define PRIME64_2   0xC2B2AE3D27D4EB4FULL
> +#define PRIME64_3   0x165667B19E3779F9ULL
> +#define PRIME64_4   0x85EBCA77C2B2AE63ULL
> +#define PRIME64_5   0x27D4EB2F165667C5ULL
> +
> +static inline uint64_t XXH64_round(uint64_t acc, uint64_t input)
> +{
> +    return rol64(acc + input * PRIME64_2, 31) * PRIME64_1;
> +}
> +
> +static inline uint64_t XXH64_mergeround(uint64_t acc, uint64_t val)
> +{
> +    return (acc ^ XXH64_round(0, val)) * PRIME64_1 + PRIME64_4;
> +}
> +
> +static inline uint64_t XXH64_avalanche(uint64_t h64)
> +{
> +    h64 ^= h64 >> 33;
> +    h64 *= PRIME64_2;
> +    h64 ^= h64 >> 29;
> +    h64 *= PRIME64_3;
> +    /* h64 ^= h64 >> 32; -- does not affect high 64 for pauth */
> +    return h64;
> +}
> +
> +static uint64_t __attribute__((noinline))
> +pauth_computepac_impdef(uint64_t data, uint64_t modifier, ARMPACKey key)
> +{
> +    uint64_t v1 = 1 + PRIME64_1 + PRIME64_2;
> +    uint64_t v2 = 1 + PRIME64_2;
> +    uint64_t v3 = 1 + 0;
> +    uint64_t v4 = 1 - PRIME64_1;
> +    uint64_t h64;
> +
> +    v1 = XXH64_round(v1, data);
> +    v2 = XXH64_round(v2, modifier);
> +    v3 = XXH64_round(v3, key.lo);
> +    v4 = XXH64_round(v4, key.hi);
> +
> +    h64 = rol64(v1, 1) + rol64(v2, 7) + rol64(v3, 12) + rol64(v4, 18);
> +    h64 = XXH64_mergeround(h64, v1);
> +    h64 = XXH64_mergeround(h64, v2);
> +    h64 = XXH64_mergeround(h64, v3);
> +    h64 = XXH64_mergeround(h64, v4);
> +
> +    return XXH64_avalanche(h64);
> +}

You might find it easier to #include "qemu/xxhash.h" which we use for tb
hashing amongst other things.  

-- 
Alex Bennée