2f760075a7
On some x86_64 hardware the RDRAND instruction returns 64bits of entropy from an on-chip random number generator. RDRAND is not recommended as an exclusive source of entropy for cryptographic applications. https://en.wikipedia.org/wiki/RdRand
57 lines
1.1 KiB
C++
57 lines
1.1 KiB
C++
/*
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* \brief Utility for reading hardware RNG
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* \date 2019-02-05
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* \author Emery Hemingway
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*/
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/*
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* Copyright (C) 2019 Genode Labs GmbH
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*
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* This file is part of the Genode OS framework, which is distributed
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* under the terms of the GNU Affero General Public License version 3.
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*/
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#ifndef _INCLUDE__SPEC__X86_64__OS__RDRAND_H_
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#define _INCLUDE__SPEC__X86_64__OS__RDRAND_H_
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#include <base/stdint.h>
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#include <base/log.h>
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namespace Genode { namespace Rdrand {
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bool supported()
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{
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unsigned int info[4] = {0, 0, 0, 0};
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asm volatile("cpuid":"=a"(info[0]),"=b"(info[1]),"=c"(info[2]),"=d"(info[3]):"a"(1),"c"(0));
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enum { RDRAND_MASK = 0x40000000 };
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return (info[2] & RDRAND_MASK);
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}
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# define _rdrand_step(x) \
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({ \
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unsigned char err; \
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asm volatile("rdrand %0; setc %1":"=r"(x), "=qm"(err)); \
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err; \
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}) \
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uint64_t random64()
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{
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uint64_t result = 0;
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enum { RETRIES = 8 };
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for (int i = 0; i < RETRIES; i++)
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if (_rdrand_step(result))
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return result;
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error("RDRAND failure");
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throw Exception();
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}
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# undef _rdrand_step
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} }
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#endif /* _INCLUDE__SPEC__X86_64__OS__RDRAND_H_ */
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