Commit 9592eef7 authored by Jason A. Donenfeld's avatar Jason A. Donenfeld
Browse files

random: remove CONFIG_ARCH_RANDOM 



When RDRAND was introduced, there was much discussion on whether it
should be trusted and how the kernel should handle that. Initially, two
mechanisms cropped up, CONFIG_ARCH_RANDOM, a compile time switch, and
"nordrand", a boot-time switch.

Later the thinking evolved. With a properly designed RNG, using RDRAND
values alone won't harm anything, even if the outputs are malicious.
Rather, the issue is whether those values are being *trusted* to be good
or not. And so a new set of options were introduced as the real
ones that people use -- CONFIG_RANDOM_TRUST_CPU and "random.trust_cpu".
With these options, RDRAND is used, but it's not always credited. So in
the worst case, it does nothing, and in the best case, maybe it helps.

Along the way, CONFIG_ARCH_RANDOM's meaning got sort of pulled into the
center and became something certain platforms force-select.

The old options don't really help with much, and it's a bit odd to have
special handling for these instructions when the kernel can deal fine
with the existence or untrusted existence or broken existence or
non-existence of that CPU capability.

Simplify the situation by removing CONFIG_ARCH_RANDOM and using the
ordinary asm-generic fallback pattern instead, keeping the two options
that are actually used. For now it leaves "nordrand" for now, as the
removal of that will take a different route.

Acked-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Acked-by: default avatarBorislav Petkov <bp@suse.de>
Acked-by: default avatarHeiko Carstens <hca@linux.ibm.com>
Acked-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarJason A. Donenfeld <Jason@zx2c4.com>
parent 829d680e

arch/arm/include/asm/archrandom.h

+2 −0
Original line number Diff line number Diff line
@@ -7,4 +7,6 @@ static inline bool __init smccc_probe_trng(void) 
	return false;

}



#include <asm-generic/archrandom.h>



#endif /* _ASM_ARCHRANDOM_H */

arch/arm64/Kconfig

+0 −8
Original line number Diff line number Diff line
@@ -1858,14 +1858,6 @@ config ARM64_E0PD 


	  This option enables E0PD for TTBR1 where available.



config ARCH_RANDOM

	bool "Enable support for random number generation"

	default y

	help

	  Random number generation (part of the ARMv8.5 Extensions)

	  provides a high bandwidth, cryptographically secure

	  hardware random number generator.



config ARM64_AS_HAS_MTE

	# Initial support for MTE went in binutils 2.32.0, checked with

	# ".arch armv8.5-a+memtag" below. However, this was incomplete

arch/arm64/include/asm/archrandom.h

+0 −10
Original line number Diff line number Diff line
@@ -2,8 +2,6 @@ 
#ifndef _ASM_ARCHRANDOM_H

#define _ASM_ARCHRANDOM_H



#ifdef CONFIG_ARCH_RANDOM



#include <linux/arm-smccc.h>

#include <linux/bug.h>

#include <linux/kernel.h>
@@ -167,12 +165,4 @@ arch_get_random_seed_long_early(unsigned long *v) 
}

#define arch_get_random_seed_long_early arch_get_random_seed_long_early



#else /* !CONFIG_ARCH_RANDOM */



static inline bool __init smccc_probe_trng(void)

{

	return false;

}



#endif /* CONFIG_ARCH_RANDOM */

#endif /* _ASM_ARCHRANDOM_H */

arch/arm64/kernel/cpufeature.c

+0 −2
Original line number Diff line number Diff line
@@ -2416,7 +2416,6 @@ static const struct arm64_cpu_capabilities arm64_features[] = { 
		.cpu_enable = cpu_enable_e0pd,

	},

#endif

#ifdef CONFIG_ARCH_RANDOM

	{

		.desc = "Random Number Generator",

		.capability = ARM64_HAS_RNG,
@@ -2428,7 +2427,6 @@ static const struct arm64_cpu_capabilities arm64_features[] = { 
		.sign = FTR_UNSIGNED,

		.min_field_value = 1,

	},

#endif

#ifdef CONFIG_ARM64_BTI

	{

		.desc = "Branch Target Identification",

arch/powerpc/Kconfig

+0 −3
Original line number Diff line number Diff line
@@ -1252,9 +1252,6 @@ config PHYSICAL_START 
	default "0x00000000"

endif



config	ARCH_RANDOM

	def_bool n



config PPC_LIB_RHEAP

	bool