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471599dc77
Commit7ca801d("[efi] Use the EFI_RNG_PROTOCOL as an entropy source if available") added EFI_RNG_PROTOCOL as an alternative entropy source via an ad-hoc mechanism specific to efi_entropy.c. Split out EFI_RNG_PROTOCOL to a separate entropy source, and allow the entropy core to handle the selection of RDRAND, EFI_RNG_PROTOCOL, or timer ticks as the active source. The fault detection logic added in commita87537d("[efi] Detect and disable seriously broken EFI_RNG_PROTOCOL implementations") may be removed completely, since the failure will already be detected by the generic ANS X9.82-mandated repetition count test and will now be handled gracefully by the entropy core. Signed-off-by: Michael Brown <mcb30@ipxe.org>
119 lines
3.5 KiB
C
119 lines
3.5 KiB
C
/*
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* Copyright (C) 2015 Michael Brown <mbrown@fensystems.co.uk>.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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* 02110-1301, USA.
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*
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* You can also choose to distribute this program under the terms of
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* the Unmodified Binary Distribution Licence (as given in the file
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* COPYING.UBDL), provided that you have satisfied its requirements.
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*/
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FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
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#include <errno.h>
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#include <ipxe/entropy.h>
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#include <ipxe/crc32.h>
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#include <ipxe/efi/efi.h>
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#include <ipxe/efi/Protocol/Rng.h>
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/** @file
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*
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* EFI random number generator protocol entropy source
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*
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*/
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struct entropy_source efirng_entropy __entropy_source ( ENTROPY_NORMAL );
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/** Random number generator protocol */
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static EFI_RNG_PROTOCOL *efirng;
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EFI_REQUEST_PROTOCOL ( EFI_RNG_PROTOCOL, &efirng );
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/** Minimum number of bytes to request from RNG
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*
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* The UEFI spec states (for no apparently good reason) that "When a
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* Deterministic Random Bit Generator (DRBG) is used on the output of
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* a (raw) entropy source, its security level must be at least 256
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* bits." The EDK2 codebase (mis)interprets this to mean that the
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* call to GetRNG() should fail if given a buffer less than 32 bytes.
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*
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* Incidentally, nothing in the EFI RNG protocol provides any way to
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* report the actual amount of entropy returned by GetRNG().
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*/
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#define EFIRNG_LEN 32
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/**
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* Enable entropy gathering
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*
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* @ret rc Return status code
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*/
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static int efirng_enable ( void ) {
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/* Check for RNG protocol support */
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if ( ! efirng ) {
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DBGC ( &efirng, "EFIRNG has no RNG protocol\n" );
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return -ENOTSUP;
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}
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/* Nothing in the EFI specification provides any clue as to
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* how much entropy will be returned by GetRNG(). Make a
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* totally uninformed (and conservative guess) that each
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* sample will contain at least one bit of entropy.
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*/
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entropy_init ( &efirng_entropy, MIN_ENTROPY ( 1.0 ) );
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return 0;
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}
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/**
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* Get noise sample from RNG protocol
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*
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* @ret noise Noise sample
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* @ret rc Return status code
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*/
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static int efirng_get_noise ( noise_sample_t *noise ) {
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uint8_t buf[EFIRNG_LEN];
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EFI_STATUS efirc;
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int rc;
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/* Sanity check */
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assert ( efirng != NULL );
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/* Get the minimum allowed number of random bytes */
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if ( ( efirc = efirng->GetRNG ( efirng, NULL, sizeof ( buf ),
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buf ) ) != 0 ) {
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rc = -EEFI ( efirc );
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DBGC ( &efirng, "ENTROPY could not read from RNG: %s\n",
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strerror ( rc ) );
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return rc;
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}
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/* Reduce random bytes to a single noise sample. This seems
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* like overkill, but we have no way of knowing how much
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* entropy is actually present in the bytes returned by the
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* RNG protocol.
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*/
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*noise = crc32_le ( 0, buf, sizeof ( buf ) );
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return 0;
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}
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/** EFI random number generator protocol entropy source */
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struct entropy_source efirng_entropy __entropy_source ( ENTROPY_NORMAL ) = {
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.name = "efirng",
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.enable = efirng_enable,
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.get_noise = efirng_get_noise,
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};
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