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plat/arm: juno: Condition Juno entropy source with CRC instructions 

The Juno Trusted Entropy Source has a bias, which makes the generated
raw numbers fail a FIPS 140-2 statistic test.

To improve the quality of the numbers, we can use the CPU's CRC
instructions, which do a decent job on conditioning the bits.

This adds a *very* simple version of arm_acle.h, which is typically
provided by the compiler, and contains the CRC instrinsics definitions
we need. We need the original version by using -nostdinc.

Change-Id: I83d3e6902d6a1164aacd5060ac13a38f0057bd1a
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
This commit is contained in:
Andre Przywara 2020-10-16 12:06:57 +01:00
parent 6630681458
commit eb18ce3283
3 changed files with 38 additions and 7 deletions
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22
include/lib/libc/arm_acle.h Normal file
View File

@ -0,0 +1,22 @@
/*
* Copyright (c) 2021 ARM Limited
*
* SPDX-License-Identifier: BSD-3-Clause
*
* The definitions below are a subset of what we would normally get by using
* the compiler's version of arm_acle.h. We can't use that directly because
* we specify -nostdinc in the Makefiles.
*
* We just define the functions we need so far.
*/
#ifndef ARM_ACLE_H
#define ARM_ACLE_H
#if !defined(__aarch64__) || defined(__clang__)
# define __crc32w __builtin_arm_crc32w
#else
# define __crc32w __builtin_aarch64_crc32w
#endif
#endif /* ARM_ACLE_H */

17
plat/arm/board/juno/juno_trng.c
View File

@ -4,6 +4,7 @@
* SPDX-License-Identifier: BSD-3-Clause
*/
#include <arm_acle.h>
#include <assert.h>
#include <stdbool.h>
#include <stdint.h>
@ -35,6 +36,8 @@ static bool output_valid(void)
return false; /* No output data available. */
}
static uint32_t crc_value = ~0U;
/*
* This function fills `buf` with 8 bytes of entropy.
* It uses the Trusted Entropy Source peripheral on Juno.
@ -69,14 +72,14 @@ bool juno_getentropy(uint64_t *buf)
return false;
}
/* XOR each two 32-bit registers together, combine the pairs */
ret = mmio_read_32(TRNG_BASE + 0);
ret ^= mmio_read_32(TRNG_BASE + 4);
ret <<= 32;
/* CRC each two 32-bit registers together, combine the pairs */
crc_value = __crc32w(crc_value, mmio_read_32(TRNG_BASE + 0));
crc_value = __crc32w(crc_value, mmio_read_32(TRNG_BASE + 4));
ret = (uint64_t)crc_value << 32;
ret |= mmio_read_32(TRNG_BASE + 8);
ret ^= mmio_read_32(TRNG_BASE + 12);
*buf = ret;
crc_value = __crc32w(crc_value, mmio_read_32(TRNG_BASE + 8));
crc_value = __crc32w(crc_value, mmio_read_32(TRNG_BASE + 12));
*buf = ret | crc_value;
/* Acknowledge current cycle, clear output registers. */
mmio_write_32(TRNG_BASE + TRNG_STATUS, 1);

6
plat/arm/board/juno/platform.mk
View File

@ -164,6 +164,12 @@ ifeq (${ALLOW_RO_XLAT_TABLES}, 1)
endif
endif
BL1_CPPFLAGS += -march=armv8-a+crc
BL2_CPPFLAGS += -march=armv8-a+crc
BL2U_CPPFLAGS += -march=armv8-a+crc
BL31_CPPFLAGS += -march=armv8-a+crc
BL32_CPPFLAGS += -march=armv8-a+crc
# Add the FDT_SOURCES and options for Dynamic Config
FDT_SOURCES += plat/arm/board/juno/fdts/${PLAT}_fw_config.dts \
plat/arm/board/juno/fdts/${PLAT}_tb_fw_config.dts