/*
* Copyright (C) 2023 Michael Brown <mbrown@fensystems.co.uk>.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301, USA.
*
* You can also choose to distribute this program under the terms of
* the Unmodified Binary Distribution Licence (as given in the file
* COPYING.UBDL), provided that you have satisfied its requirements.
*/
FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
/** @file
*
* Hardware random number generator
*
*/
#include <errno.h>
#include <ipxe/cpuid.h>
#include <ipxe/entropy.h>
#include <ipxe/drbg.h>
struct entropy_source rdrand_entropy __entropy_source ( ENTROPY_PREFERRED );
/** Number of times to retry RDRAND instruction */
#define RDRAND_RETRY_COUNT 16
/** Colour for debug messages */
#define colour &rdrand_entropy
/**
* Enable entropy gathering
*
* @ret rc Return status code
*/
static int rdrand_entropy_enable ( void ) {
struct x86_features features;
/* Check that RDRAND is supported */
x86_features ( &features );
if ( ! ( features.intel.ecx & CPUID_FEATURES_INTEL_ECX_RDRAND ) ) {
DBGC ( colour, "RDRAND not supported\n" );
return -ENOTSUP;
}
/* Data returned by RDRAND is theoretically full entropy, up
* to a security strength of 128 bits, so assume that each
* sample contains exactly 8 bits of entropy.
*/
if ( DRBG_SECURITY_STRENGTH > 128 )
return -ENOTSUP;
entropy_init ( &rdrand_entropy, MIN_ENTROPY ( 8.0 ) );
return 0;
}
/**
* Get noise sample
*
* @ret noise Noise sample
* @ret rc Return status code
*/
static int rdrand_get_noise ( noise_sample_t *noise ) {
unsigned int result;
unsigned int discard_c;
unsigned int ok;
/* Issue RDRAND, retrying until CF is set */
__asm__ ( "\n1:\n\t"
"rdrand %0\n\t"
"sbb %1, %1\n\t"
"loopz 1b\n\t"
: "=r" ( result ), "=r" ( ok ), "=c" ( discard_c )
: "2" ( RDRAND_RETRY_COUNT ) );
if ( ! ok ) {
DBGC ( colour, "RDRAND failed to become ready\n" );
return -EBUSY;
}
*noise = result;
return 0;
}
/** Hardware random number generator entropy source */
struct entropy_source rdrand_entropy __entropy_source ( ENTROPY_PREFERRED ) = {
.name = "rdrand",
.enable = rdrand_entropy_enable,
.get_noise = rdrand_get_noise,
};
