Richard Henderson <richard.hender...@linaro.org> writes:
> On 8/12/20 2:49 AM, Alex Bennée wrote:
>>
>> Richard Henderson <richard.hender...@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.hender...@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.
>
> First, that's the 32-bit version, XXH32.
Ahh I missed that detail.
> Second, we define xxhash7 there; we would need xxhash8 here.
We could at least put the code in the header with the others.
>
>
> r~
--
Alex Bennée
