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/*
* (C) 2019 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/internal/p9_darn.h>
#include <botan/cpuid.h>
namespace Botan {
namespace {
bool read_darn(secure_vector<uint64_t>& seed)
{
const size_t DARN_RETRIES = 512;
for(size_t i = 0; i != DARN_RETRIES; ++i)
{
uint64_t r = 0;
// DARN 0: 32-bit conditioned, 1: 64-bit condition, 2: 64-bit raw (ala RDSEED)
asm volatile("darn %0, 2" : "=r" (r));
// DARN indicates error by 0xFF..FF, ie is biased (!?!?)
if((~r) != 0)
{
seed.push_back(r);
return true;
}
}
return false; // failed to produce an output after many attempts
}
}
size_t POWER9_DARN::poll(RandomNumberGenerator& rng)
{
const size_t DARN_BYTES = 1024;
static_assert(DARN_BYTES % 8 == 0, "Bad DARN configuration");
if(CPUID::has_darn_rng())
{
secure_vector<uint64_t> seed;
seed.reserve(DARN_BYTES / 8);
for(size_t p = 0; p != DARN_BYTES / 8; ++p)
{
if(!read_darn(seed))
break;
}
if(seed.size() > 0)
{
rng.add_entropy(reinterpret_cast<const uint8_t*>(seed.data()),
seed.size() * sizeof(uint32_t));
}
}
// DARN is used but not trusted
return 0;
}
}
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