diff options
Diffstat (limited to 'qemu/roms/ipxe/src/arch/x86/interface/efi/efi_entropy.c')
| -rw-r--r-- | qemu/roms/ipxe/src/arch/x86/interface/efi/efi_entropy.c | 223 |
1 files changed, 223 insertions, 0 deletions
diff --git a/qemu/roms/ipxe/src/arch/x86/interface/efi/efi_entropy.c b/qemu/roms/ipxe/src/arch/x86/interface/efi/efi_entropy.c new file mode 100644 index 000000000..a54bd12e6 --- /dev/null +++ b/qemu/roms/ipxe/src/arch/x86/interface/efi/efi_entropy.c @@ -0,0 +1,223 @@ +/* + * 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 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 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; + + /* 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 TSC low-order bits */ + __asm__ __volatile__ ( "rdtsc" : "=a" ( low ), "=d" ( discard_d ) ); + + 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 ); |