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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.
- */
-
- 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
- *
- * EFI entropy source
- *
- */
-
- /** 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
-
- /** 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
-
- /** Event used to wait for timer tick */
- static EFI_EVENT tick;
-
- /**
- * 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;
-
- DBGC ( &tick, "ENTROPY %s RNG protocol\n",
- ( efirng ? "has" : "has no" ) );
-
- /* 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;
- }
-
- return 0;
- }
-
- /**
- * Disable entropy gathering
- *
- */
- static void efi_entropy_disable ( void ) {
- EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
-
- /* Close timer tick event */
- bs->CloseEvent ( tick );
- }
-
- /**
- * Wait for a timer tick
- *
- * @ret low CPU profiling low-order bits, or negative error
- */
- static int efi_entropy_tick ( void ) {
- EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
- UINTN index;
- uint16_t low;
- EFI_STATUS efirc;
- int rc;
-
- /* 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;
- }
-
- /* Get current CPU profiling timestamp low-order bits */
- low = profile_timestamp();
-
- return low;
- }
-
- /**
- * Get noise sample from timer ticks
- *
- * @ret noise Noise sample
- * @ret rc Return status code
- */
- static int efi_get_noise_ticks ( noise_sample_t *noise ) {
- int before;
- int after;
- int rc;
-
- /* Wait for a timer tick */
- before = efi_entropy_tick();
- if ( before < 0 ) {
- rc = before;
- return rc;
- }
-
- /* Wait for another timer tick */
- after = efi_entropy_tick();
- if ( after < 0 ) {
- rc = after;
- return rc;
- }
-
- /* Use TSC delta as noise sample */
- *noise = ( after - before );
-
- 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 ) {
- 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;
- }
-
- /* 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;
- }
-
- 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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