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[efi] Split out EFI_RNG_PROTOCOL as a separate entropy source 

Commit 7ca801d ("[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 commit a87537d ("[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>
pull/905/head
Michael Brown 2023-02-20 14:08:49 +00:00
parent 7d71cf318a
commit 471599dc77
5 changed files with 130 additions and 92 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
src/config/config_entropy.c
View File

@ -37,9 +37,12 @@ PROVIDE_REQUIRING_SYMBOL();
#ifdef ENTROPY_RTC
REQUIRE_OBJECT ( rtc_entropy );
#endif
#ifdef ENTROPY_EFI
#ifdef ENTROPY_EFITICK
REQUIRE_OBJECT ( efi_entropy );
#endif
#ifdef ENTROPY_EFIRNG
REQUIRE_OBJECT ( efi_rng );
#endif
#ifdef ENTROPY_LINUX
REQUIRE_OBJECT ( linux_entropy );
#endif

3
src/config/defaults/efi.h
View File

@ -19,7 +19,8 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
#define SMBIOS_EFI
#define SANBOOT_EFI
#define BOFM_EFI
#define ENTROPY_EFI
#define ENTROPY_EFITICK
#define ENTROPY_EFIRNG
#define TIME_EFI
#define REBOOT_EFI
#define ACPI_EFI

1
src/include/ipxe/errfile.h
View File

@ -403,6 +403,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
#define ERRFILE_pci_cmd ( ERRFILE_OTHER | 0x00590000 )
#define ERRFILE_dhe ( ERRFILE_OTHER | 0x005a0000 )
#define ERRFILE_efi_cmdline ( ERRFILE_OTHER | 0x005b0000 )
#define ERRFILE_efi_rng ( ERRFILE_OTHER | 0x005c0000 )
/** @} */

95
src/interface/efi/efi_entropy.c
View File

@ -25,10 +25,8 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
#include <errno.h>
#include <ipxe/entropy.h>
#include <ipxe/crc32.h>
#include <ipxe/profile.h>
#include <ipxe/efi/efi.h>
#include <ipxe/efi/Protocol/Rng.h>
/** @file
*
@ -36,24 +34,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
*
*/
struct entropy_source efi_entropy __entropy_source ( ENTROPY_NORMAL );
/** Random number generator protocol */
static EFI_RNG_PROTOCOL *efirng;
EFI_REQUEST_PROTOCOL ( EFI_RNG_PROTOCOL, &efirng );
/** Minimum number of bytes to request from RNG
*
* The UEFI spec states (for no apparently good reason) that "When a
* Deterministic Random Bit Generator (DRBG) is used on the output of
* a (raw) entropy source, its security level must be at least 256
* bits." The EDK2 codebase (mis)interprets this to mean that the
* call to GetRNG() should fail if given a buffer less than 32 bytes.
*
* Incidentally, nothing in the EFI RNG protocol provides any way to
* report the actual amount of entropy returned by GetRNG().
*/
#define EFI_ENTROPY_RNG_LEN 32
struct entropy_source efitick_entropy __entropy_source ( ENTROPY_FALLBACK );
/** Time (in 100ns units) to delay waiting for timer tick
*
@ -78,9 +59,6 @@ static int efi_entropy_enable ( void ) {
EFI_STATUS efirc;
int rc;
DBGC ( &tick, "ENTROPY %s RNG protocol\n",
( efirng ? "has" : "has no" ) );
/* Drop to external TPL to allow timer tick event to take place */
bs->RestoreTPL ( efi_external_tpl );
@ -97,7 +75,7 @@ static int efi_entropy_enable ( void ) {
* RTC-based entropy source, and so assume the same
* min-entropy per sample.
*/
entropy_init ( &efi_entropy, MIN_ENTROPY ( 1.3 ) );
entropy_init ( &efitick_entropy, MIN_ENTROPY ( 1.3 ) );
return 0;
}
@ -155,7 +133,7 @@ static int efi_entropy_tick ( void ) {
* @ret noise Noise sample
* @ret rc Return status code
*/
static int efi_get_noise_ticks ( noise_sample_t *noise ) {
static int efi_get_noise ( noise_sample_t *noise ) {
int before;
int after;
int rc;
@ -180,72 +158,9 @@ static int efi_get_noise_ticks ( noise_sample_t *noise ) {
return 0;
}
/**
* Get noise sample from RNG protocol
*
* @ret noise Noise sample
* @ret rc Return status code
*/
static int efi_get_noise_rng ( noise_sample_t *noise ) {
static uint8_t prev[EFI_ENTROPY_RNG_LEN];
uint8_t buf[EFI_ENTROPY_RNG_LEN];
EFI_STATUS efirc;
int rc;
/* Fail if we have no EFI RNG protocol */
if ( ! efirng )
return -ENOTSUP;
/* Get the minimum allowed number of random bytes */
if ( ( efirc = efirng->GetRNG ( efirng, NULL, EFI_ENTROPY_RNG_LEN,
buf ) ) != 0 ) {
rc = -EEFI ( efirc );
DBGC ( &tick, "ENTROPY could not read from RNG: %s\n",
strerror ( rc ) );
return rc;
}
/* Fail (and permanently disable the EFI RNG) if we get
* consecutive identical results.
*/
if ( memcmp ( buf, prev, sizeof ( buf ) ) == 0 ) {
DBGC ( &tick, "ENTROPY detected broken EFI RNG:\n" );
DBGC_HDA ( &tick, 0, buf, sizeof ( buf ) );
efirng = NULL;
return -EIO;
}
memcpy ( prev, buf, sizeof ( prev ) );
/* Reduce random bytes to a single noise sample. This seems
* like overkill, but we have no way of knowing how much
* entropy is actually present in the bytes returned by the
* RNG protocol.
*/
*noise = crc32_le ( 0, buf, sizeof ( buf ) );
return 0;
}
/**
* Get noise sample
*
* @ret noise Noise sample
* @ret rc Return status code
*/
static int efi_get_noise ( noise_sample_t *noise ) {
int rc;
/* Try RNG first, falling back to timer ticks */
if ( ( ( rc = efi_get_noise_rng ( noise ) ) != 0 ) &&
( ( rc = efi_get_noise_ticks ( noise ) ) != 0 ) )
return rc;
return 0;
}
/** EFI entropy source */
struct entropy_source efi_entropy __entropy_source ( ENTROPY_NORMAL ) = {
.name = "efi",
struct entropy_source efitick_entropy __entropy_source ( ENTROPY_FALLBACK ) = {
.name = "efitick",
.enable = efi_entropy_enable,
.disable = efi_entropy_disable,
.get_noise = efi_get_noise,

118
src/interface/efi/efi_rng.c 100644
View File

@ -0,0 +1,118 @@
/*
* 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.
*/
FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
#include <errno.h>
#include <ipxe/entropy.h>
#include <ipxe/crc32.h>
#include <ipxe/efi/efi.h>
#include <ipxe/efi/Protocol/Rng.h>
/** @file
*
* EFI random number generator protocol entropy source
*
*/
struct entropy_source efirng_entropy __entropy_source ( ENTROPY_NORMAL );
/** Random number generator protocol */
static EFI_RNG_PROTOCOL *efirng;
EFI_REQUEST_PROTOCOL ( EFI_RNG_PROTOCOL, &efirng );
/** Minimum number of bytes to request from RNG
*
* The UEFI spec states (for no apparently good reason) that "When a
* Deterministic Random Bit Generator (DRBG) is used on the output of
* a (raw) entropy source, its security level must be at least 256
* bits." The EDK2 codebase (mis)interprets this to mean that the
* call to GetRNG() should fail if given a buffer less than 32 bytes.
*
* Incidentally, nothing in the EFI RNG protocol provides any way to
* report the actual amount of entropy returned by GetRNG().
*/
#define EFIRNG_LEN 32
/**
* Enable entropy gathering
*
* @ret rc Return status code
*/
static int efirng_enable ( void ) {
/* Check for RNG protocol support */
if ( ! efirng ) {
DBGC ( &efirng, "EFIRNG has no RNG protocol\n" );
return -ENOTSUP;
}
/* Nothing in the EFI specification provides any clue as to
* how much entropy will be returned by GetRNG(). Make a
* totally uninformed (and conservative guess) that each
* sample will contain at least one bit of entropy.
*/
entropy_init ( &efirng_entropy, MIN_ENTROPY ( 1.0 ) );
return 0;
}
/**
* Get noise sample from RNG protocol
*
* @ret noise Noise sample
* @ret rc Return status code
*/
static int efirng_get_noise ( noise_sample_t *noise ) {
uint8_t buf[EFIRNG_LEN];
EFI_STATUS efirc;
int rc;
/* Sanity check */
assert ( efirng != NULL );
/* Get the minimum allowed number of random bytes */
if ( ( efirc = efirng->GetRNG ( efirng, NULL, sizeof ( buf ),
buf ) ) != 0 ) {
rc = -EEFI ( efirc );
DBGC ( &efirng, "ENTROPY could not read from RNG: %s\n",
strerror ( rc ) );
return rc;
}
/* Reduce random bytes to a single noise sample. This seems
* like overkill, but we have no way of knowing how much
* entropy is actually present in the bytes returned by the
* RNG protocol.
*/
*noise = crc32_le ( 0, buf, sizeof ( buf ) );
return 0;
}
/** EFI random number generator protocol entropy source */
struct entropy_source efirng_entropy __entropy_source ( ENTROPY_NORMAL ) = {
.name = "efirng",
.enable = efirng_enable,
.get_noise = efirng_get_noise,
};