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Originally-implemented-by: Jarrod Johnson <jbjohnso@us.ibm.com> Signed-off-by: Michael Brown <mcb30@ipxe.org>
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/* | ||
* Copyright (C) 2015 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 (at your option) 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. | ||
*/ | ||
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FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL ); | ||
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#include <errno.h> | ||
#include <ipxe/entropy.h> | ||
#include <ipxe/efi/efi.h> | ||
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/** @file | ||
* | ||
* EFI entropy source | ||
* | ||
*/ | ||
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/** Time (in 100ns units) to delay waiting for timer tick | ||
* | ||
* In theory, UEFI allows us to specify a trigger time of zero to | ||
* simply wait for the next timer tick. In practice, specifying zero | ||
* seems to often return immediately, which produces almost no | ||
* entropy. Specify a delay of 1000ns to try to force an existent | ||
* delay. | ||
*/ | ||
#define EFI_ENTROPY_TRIGGER_TIME 10 | ||
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/** Event used to wait for timer tick */ | ||
static EFI_EVENT tick; | ||
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/** | ||
* Enable entropy gathering | ||
* | ||
* @ret rc Return status code | ||
*/ | ||
static int efi_entropy_enable ( void ) { | ||
EFI_BOOT_SERVICES *bs = efi_systab->BootServices; | ||
EFI_STATUS efirc; | ||
int rc; | ||
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/* Create timer tick event */ | ||
if ( ( efirc = bs->CreateEvent ( EVT_TIMER, TPL_NOTIFY, NULL, NULL, | ||
&tick ) ) != 0 ) { | ||
rc = -EEFI ( efirc ); | ||
DBGC ( &tick, "ENTROPY could not create event: %s\n", | ||
strerror ( rc ) ); | ||
return rc; | ||
} | ||
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return 0; | ||
} | ||
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/** | ||
* Disable entropy gathering | ||
* | ||
*/ | ||
static void efi_entropy_disable ( void ) { | ||
EFI_BOOT_SERVICES *bs = efi_systab->BootServices; | ||
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/* Close timer tick event */ | ||
bs->CloseEvent ( tick ); | ||
} | ||
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/** | ||
* Wait for an RTC tick | ||
* | ||
* @ret low TSC low-order bits, or negative error | ||
*/ | ||
static int efi_entropy_tick ( void ) { | ||
EFI_BOOT_SERVICES *bs = efi_systab->BootServices; | ||
UINTN index; | ||
uint16_t low; | ||
uint32_t discard_d; | ||
EFI_STATUS efirc; | ||
int rc; | ||
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/* Wait for next timer tick */ | ||
if ( ( efirc = bs->SetTimer ( tick, TimerRelative, | ||
EFI_ENTROPY_TRIGGER_TIME ) ) != 0 ) { | ||
rc = -EEFI ( efirc ); | ||
DBGC ( &tick, "ENTROPY could not set timer: %s\n", | ||
strerror ( rc ) ); | ||
return rc; | ||
} | ||
if ( ( efirc = bs->WaitForEvent ( 1, &tick, &index ) ) != 0 ) { | ||
rc = -EEFI ( efirc ); | ||
DBGC ( &tick, "ENTROPY could not wait for timer tick: %s\n", | ||
strerror ( rc ) ); | ||
return rc; | ||
} | ||
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/* Get current TSC low-order bits */ | ||
__asm__ __volatile__ ( "rdtsc" : "=a" ( low ), "=d" ( discard_d ) ); | ||
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return low; | ||
} | ||
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/** | ||
* Get noise sample | ||
* | ||
* @ret noise Noise sample | ||
* @ret rc Return status code | ||
*/ | ||
static int efi_get_noise ( noise_sample_t *noise ) { | ||
int before; | ||
int after; | ||
int rc; | ||
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/* Wait for a timer tick */ | ||
before = efi_entropy_tick(); | ||
if ( before < 0 ) { | ||
rc = before; | ||
return rc; | ||
} | ||
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/* Wait for another timer tick */ | ||
after = efi_entropy_tick(); | ||
if ( after < 0 ) { | ||
rc = after; | ||
return rc; | ||
} | ||
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/* Use TSC delta as noise sample */ | ||
*noise = ( after - before ); | ||
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return 0; | ||
} | ||
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PROVIDE_ENTROPY_INLINE ( efi, min_entropy_per_sample ); | ||
PROVIDE_ENTROPY ( efi, entropy_enable, efi_entropy_enable ); | ||
PROVIDE_ENTROPY ( efi, entropy_disable, efi_entropy_disable ); | ||
PROVIDE_ENTROPY ( efi, get_noise, efi_get_noise ); |
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#ifndef _IPXE_EFI_ENTROPY_H | ||
#define _IPXE_EFI_ENTROPY_H | ||
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/** @file | ||
* | ||
* EFI entropy source | ||
* | ||
*/ | ||
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FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL ); | ||
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#include <stdint.h> | ||
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#ifdef ENTROPY_EFI | ||
#define ENTROPY_PREFIX_efi | ||
#else | ||
#define ENTROPY_PREFIX_efi __efi_ | ||
#endif | ||
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/** | ||
* min-entropy per sample | ||
* | ||
* @ret min_entropy min-entropy of each sample | ||
*/ | ||
static inline __always_inline double | ||
ENTROPY_INLINE ( efi, min_entropy_per_sample ) ( void ) { | ||
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/* We use essentially the same mechanism as for the BIOS | ||
* RTC-based entropy source, and so assume the same | ||
* min-entropy per sample. | ||
*/ | ||
return 1.3; | ||
} | ||
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#endif /* _IPXE_EFI_ENTROPY_H */ |
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