[PATCH v5] random: remove CONFIG_ARCH_RANDOM

Jason A. Donenfeld
2022-07-08T00:40:54Z

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.

Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Acked-by: Borislav Petkov <bp@suse.de>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
Changes v4->v5:
- Squelch warning on ARCH=um.
- Include asm-generic on arm instead of duplicating code.
Changes v3->v4:
- Use asm-generic for fallback.
Changes v2->v3:
- Keep compiling on archs with no ARCH_RANDOM.
Changes v1->v2:
- Get rid of nordrand change for now.

arch/arm/include/asm/archrandom.h | 2 ++
arch/arm64/Kconfig | 8 ------
arch/arm64/include/asm/archrandom.h | 10 --------
arch/arm64/kernel/cpufeature.c | 2 --
arch/powerpc/Kconfig | 3 ---
arch/powerpc/include/asm/archrandom.h | 3 ---
arch/powerpc/include/asm/machdep.h | 2 --
arch/powerpc/platforms/microwatt/Kconfig | 1 -
arch/powerpc/platforms/powernv/Kconfig | 1 -
arch/powerpc/platforms/pseries/Kconfig | 1 -
arch/s390/Kconfig | 15 -----------
arch/s390/configs/zfcpdump_defconfig | 1 -
arch/s390/crypto/Makefile | 2 +-
arch/s390/include/asm/archrandom.h | 3 ---
arch/x86/Kconfig | 9 -------
arch/x86/include/asm/archrandom.h | 14 +++--------
arch/x86/kernel/cpu/rdrand.c | 2 --
drivers/char/Kconfig | 1 -
drivers/char/hw_random/s390-trng.c | 9 -------
include/asm-generic/Kbuild | 1 +
include/asm-generic/archrandom.h | 25 +++++++++++++++++++
include/linux/random.h | 9 +------
.../selftests/wireguard/qemu/kernel.config | 1 -
23 files changed, 34 insertions(+), 91 deletions(-)
create mode 100644 include/asm-generic/archrandom.h

diff --git a/arch/arm/include/asm/archrandom.h b/arch/arm/include/asm/archrandom.h
index a8e84ca5c2ee..cc4714eb1a75 100644
--- a/arch/arm/include/asm/archrandom.h
+++ b/arch/arm/include/asm/archrandom.h
@@ -7,4 +7,6 @@ static inline bool __init smccc_probe_trng(void)
return false;
}

+#include <asm-generic/archrandom.h>
+
#endif /* _ASM_ARCHRANDOM_H */
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 1652a9800ebe..1880f71c2547 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -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
diff --git a/arch/arm64/include/asm/archrandom.h b/arch/arm64/include/asm/archrandom.h
index 3a6b6d38c5b8..c3b9fa56af67 100644
--- a/arch/arm64/include/asm/archrandom.h
+++ b/arch/arm64/include/asm/archrandom.h
@@ -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 */
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 8d88433de81d..0e9462abeb77 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -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",
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 7aa12e88c580..623deb5bedf6 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -1252,9 +1252,6 @@ config PHYSICAL_START
default "0x00000000"
endif

-config ARCH_RANDOM
- def_bool n
-
config PPC_LIB_RHEAP
bool

diff --git a/arch/powerpc/include/asm/archrandom.h b/arch/powerpc/include/asm/archrandom.h
index 9a53e29680f4..25ba65df6b1a 100644
--- a/arch/powerpc/include/asm/archrandom.h
+++ b/arch/powerpc/include/asm/archrandom.h
@@ -2,8 +2,6 @@
#ifndef _ASM_POWERPC_ARCHRANDOM_H
#define _ASM_POWERPC_ARCHRANDOM_H

-#ifdef CONFIG_ARCH_RANDOM
-
#include <asm/machdep.h>

static inline bool __must_check arch_get_random_long(unsigned long *v)
@@ -35,7 +33,6 @@ static inline bool __must_check arch_get_random_seed_int(unsigned int *v)

return rc;
}
-#endif /* CONFIG_ARCH_RANDOM */

#ifdef CONFIG_PPC_POWERNV
int powernv_hwrng_present(void);
diff --git a/arch/powerpc/include/asm/machdep.h b/arch/powerpc/include/asm/machdep.h
index 358d171ae8e0..6c1002043367 100644
--- a/arch/powerpc/include/asm/machdep.h
+++ b/arch/powerpc/include/asm/machdep.h
@@ -200,9 +200,7 @@ struct machdep_calls {
ssize_t (*cpu_release)(const char *, size_t);
#endif

-#ifdef CONFIG_ARCH_RANDOM
int (*get_random_seed)(unsigned long *v);
-#endif
};

extern void e500_idle(void);
diff --git a/arch/powerpc/platforms/microwatt/Kconfig b/arch/powerpc/platforms/microwatt/Kconfig
index 5e320f49583a..6af443a1db99 100644
--- a/arch/powerpc/platforms/microwatt/Kconfig
+++ b/arch/powerpc/platforms/microwatt/Kconfig
@@ -6,7 +6,6 @@ config PPC_MICROWATT
select PPC_ICS_NATIVE
select PPC_ICP_NATIVE
select PPC_UDBG_16550
- select ARCH_RANDOM
help
This option enables support for FPGA-based Microwatt implementations.

diff --git a/arch/powerpc/platforms/powernv/Kconfig b/arch/powerpc/platforms/powernv/Kconfig
index 161dfe024085..e1a05c5a9004 100644
--- a/arch/powerpc/platforms/powernv/Kconfig
+++ b/arch/powerpc/platforms/powernv/Kconfig
@@ -12,7 +12,6 @@ config PPC_POWERNV
select EPAPR_BOOT
select PPC_INDIRECT_PIO
select PPC_UDBG_16550
- select ARCH_RANDOM
select CPU_FREQ
select PPC_DOORBELL
select MMU_NOTIFIER
diff --git a/arch/powerpc/platforms/pseries/Kconfig b/arch/powerpc/platforms/pseries/Kconfig
index f7fd91d153a4..f4a647c1f0b2 100644
--- a/arch/powerpc/platforms/pseries/Kconfig
+++ b/arch/powerpc/platforms/pseries/Kconfig
@@ -19,7 +19,6 @@ config PPC_PSERIES
select PPC_UDBG_16550
select PPC_DOORBELL
select HOTPLUG_CPU
- select ARCH_RANDOM
select FORCE_SMP
select SWIOTLB
default y
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 8cd9e56c629b..9b6e4e7cb17b 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -507,21 +507,6 @@ config KEXEC_SIG
verification for the corresponding kernel image type being
loaded in order for this to work.

-config ARCH_RANDOM
- def_bool y
- prompt "s390 architectural random number generation API"
- help
- Enable the s390 architectural random number generation API
- to provide random data for all consumers within the Linux
- kernel.
-
- When enabled the arch_random_* functions declared in linux/random.h
- are implemented. The implementation is based on the s390 CPACF
- instruction subfunction TRNG which provides a real true random
- number generator.
-
- If unsure, say Y.
-
config KERNEL_NOBP
def_bool n
prompt "Enable modified branch prediction for the kernel by default"
diff --git a/arch/s390/configs/zfcpdump_defconfig b/arch/s390/configs/zfcpdump_defconfig
index a87fcc45e307..f4976f611b94 100644
--- a/arch/s390/configs/zfcpdump_defconfig
+++ b/arch/s390/configs/zfcpdump_defconfig
@@ -15,7 +15,6 @@ CONFIG_TUNE_ZEC12=y
# CONFIG_COMPAT is not set
CONFIG_NR_CPUS=2
CONFIG_HZ_100=y
-# CONFIG_ARCH_RANDOM is not set
# CONFIG_RELOCATABLE is not set
# CONFIG_CHSC_SCH is not set
# CONFIG_SCM_BUS is not set
diff --git a/arch/s390/crypto/Makefile b/arch/s390/crypto/Makefile
index c63abfeb6d17..1b1cc478fa94 100644
--- a/arch/s390/crypto/Makefile
+++ b/arch/s390/crypto/Makefile
@@ -15,7 +15,7 @@ obj-$(CONFIG_CRYPTO_CHACHA_S390) += chacha_s390.o
obj-$(CONFIG_S390_PRNG) += prng.o
obj-$(CONFIG_CRYPTO_GHASH_S390) += ghash_s390.o
obj-$(CONFIG_CRYPTO_CRC32_S390) += crc32-vx_s390.o
-obj-$(CONFIG_ARCH_RANDOM) += arch_random.o
+obj-y += arch_random.o

crc32-vx_s390-y := crc32-vx.o crc32le-vx.o crc32be-vx.o
chacha_s390-y := chacha-glue.o chacha-s390.o
diff --git a/arch/s390/include/asm/archrandom.h b/arch/s390/include/asm/archrandom.h
index 2c6e1c6ecbe7..0a1c2e66c709 100644
--- a/arch/s390/include/asm/archrandom.h
+++ b/arch/s390/include/asm/archrandom.h
@@ -11,8 +11,6 @@
#ifndef _ASM_S390_ARCHRANDOM_H
#define _ASM_S390_ARCHRANDOM_H

-#ifdef CONFIG_ARCH_RANDOM
-
#include <linux/static_key.h>
#include <linux/atomic.h>
#include <asm/cpacf.h>
@@ -50,5 +48,4 @@ static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
return false;
}

-#endif /* CONFIG_ARCH_RANDOM */
#endif /* _ASM_S390_ARCHRANDOM_H */
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index be0b95e51df6..59b82135c814 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1833,15 +1833,6 @@ config ARCH_USES_PG_UNCACHED
def_bool y
depends on X86_PAT

-config ARCH_RANDOM
- def_bool y
- prompt "x86 architectural random number generator" if EXPERT
- help
- Enable the x86 architectural RDRAND instruction
- (Intel Bull Mountain technology) to generate random numbers.
- If supported, this is a high bandwidth, cryptographically
- secure hardware random number generator.
-
config X86_UMIP
def_bool y
prompt "User Mode Instruction Prevention" if EXPERT
diff --git a/arch/x86/include/asm/archrandom.h b/arch/x86/include/asm/archrandom.h
index ebc248e49549..fb235b696175 100644
--- a/arch/x86/include/asm/archrandom.h
+++ b/arch/x86/include/asm/archrandom.h
@@ -65,10 +65,8 @@ static inline bool __must_check rdseed_int(unsigned int *v)

/*
* These are the generic interfaces; they must not be declared if the
- * stubs in <linux/random.h> are to be invoked,
- * i.e. CONFIG_ARCH_RANDOM is not defined.
+ * stubs in <linux/random.h> are to be invoked.
*/
-#ifdef CONFIG_ARCH_RANDOM

static inline bool __must_check arch_get_random_long(unsigned long *v)
{
@@ -90,12 +88,8 @@ static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
return static_cpu_has(X86_FEATURE_RDSEED) ? rdseed_int(v) : false;
}

-extern void x86_init_rdrand(struct cpuinfo_x86 *c);
-
-#else /* !CONFIG_ARCH_RANDOM */
-
-static inline void x86_init_rdrand(struct cpuinfo_x86 *c) { }
-
-#endif /* !CONFIG_ARCH_RANDOM */
+#ifndef CONFIG_UML
+void x86_init_rdrand(struct cpuinfo_x86 *c);
+#endif

#endif /* ASM_X86_ARCHRANDOM_H */
diff --git a/arch/x86/kernel/cpu/rdrand.c b/arch/x86/kernel/cpu/rdrand.c
index 23b901cc46df..6f4b196fe97d 100644
--- a/arch/x86/kernel/cpu/rdrand.c
+++ b/arch/x86/kernel/cpu/rdrand.c
@@ -20,7 +20,6 @@
* If it fails, it is simple to disable RDRAND and RDSEED here.
*/

-#ifdef CONFIG_ARCH_RANDOM
void x86_init_rdrand(struct cpuinfo_x86 *c)
{
enum { SAMPLES = 8, MIN_CHANGE = 5 };
@@ -60,4 +59,3 @@ void x86_init_rdrand(struct cpuinfo_x86 *c)
pr_emerg("RDRAND and RDSEED are not reliable on this platform; disabling.\n");
}
}
-#endif
diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index 0b6c03643ddc..30192e123e5f 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -431,7 +431,6 @@ config ADI
config RANDOM_TRUST_CPU
bool "Initialize RNG using CPU RNG instructions"
default y
- depends on ARCH_RANDOM
help
Initialize the RNG using random numbers supplied by the CPU's
RNG instructions (e.g. RDRAND), if supported and available. These
diff --git a/drivers/char/hw_random/s390-trng.c b/drivers/char/hw_random/s390-trng.c
index 2beaa35c0d74..488808dc17a2 100644
--- a/drivers/char/hw_random/s390-trng.c
+++ b/drivers/char/hw_random/s390-trng.c
@@ -108,7 +108,6 @@ static ssize_t trng_counter_show(struct device *dev,
{
u64 dev_counter = atomic64_read(&trng_dev_counter);
u64 hwrng_counter = atomic64_read(&trng_hwrng_counter);
-#if IS_ENABLED(CONFIG_ARCH_RANDOM)
u64 arch_counter = atomic64_read(&s390_arch_random_counter);

return sysfs_emit(buf,
@@ -118,14 +117,6 @@ static ssize_t trng_counter_show(struct device *dev,
"total: %llu\n",
dev_counter, hwrng_counter, arch_counter,
dev_counter + hwrng_counter + arch_counter);
-#else
- return sysfs_emit(buf,
- "trng: %llu\n"
- "hwrng: %llu\n"
- "total: %llu\n",
- dev_counter, hwrng_counter,
- dev_counter + hwrng_counter);
-#endif
}
static DEVICE_ATTR(byte_counter, 0444, trng_counter_show, NULL);

diff --git a/include/asm-generic/Kbuild b/include/asm-generic/Kbuild
index 8e47d483b524..36db8b9eb68a 100644
--- a/include/asm-generic/Kbuild
+++ b/include/asm-generic/Kbuild
@@ -5,6 +5,7 @@
# asm headers from the host architecutre.)

mandatory-y += atomic.h
+mandatory-y += archrandom.h
mandatory-y += barrier.h
mandatory-y += bitops.h
mandatory-y += bug.h
diff --git a/include/asm-generic/archrandom.h b/include/asm-generic/archrandom.h
new file mode 100644
index 000000000000..3a5ee202dd86
--- /dev/null
+++ b/include/asm-generic/archrandom.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_GENERIC_ARCHRANDOM_H__
+#define __ASM_GENERIC_ARCHRANDOM_H__
+
+static inline bool __must_check arch_get_random_long(unsigned long *v)
+{
+ return false;
+}
+
+static inline bool __must_check arch_get_random_int(unsigned int *v)
+{
+ return false;
+}
+
+static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
+{
+ return false;
+}
+
+static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
+{
+ return false;
+}
+
+#endif
diff --git a/include/linux/random.h b/include/linux/random.h
index 20e389a14e5c..865770e29f3e 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -106,14 +106,7 @@ declare_get_random_var_wait(long, unsigned long)
*/
#include <linux/prandom.h>

-#ifdef CONFIG_ARCH_RANDOM
-# include <asm/archrandom.h>
-#else
-static inline bool __must_check arch_get_random_long(unsigned long *v) { return false; }
-static inline bool __must_check arch_get_random_int(unsigned int *v) { return false; }
-static inline bool __must_check arch_get_random_seed_long(unsigned long *v) { return false; }
-static inline bool __must_check arch_get_random_seed_int(unsigned int *v) { return false; }
-#endif
+#include <asm/archrandom.h>

/*
* Called from the boot CPU during startup; not valid to call once
diff --git a/tools/testing/selftests/wireguard/qemu/kernel.config b/tools/testing/selftests/wireguard/qemu/kernel.config
index bad88f4b0a03..e1858ce7003f 100644
--- a/tools/testing/selftests/wireguard/qemu/kernel.config
+++ b/tools/testing/selftests/wireguard/qemu/kernel.config
@@ -58,7 +58,6 @@ CONFIG_NO_HZ_IDLE=y
CONFIG_NO_HZ_FULL=n
CONFIG_HZ_PERIODIC=n
CONFIG_HIGH_RES_TIMERS=y
-CONFIG_ARCH_RANDOM=y
CONFIG_FILE_LOCKING=y
CONFIG_POSIX_TIMERS=y
CONFIG_DEVTMPFS=y
--
2.35.1