commit e4f74400308cb8abde5fdc9cad609c2aba32110c upstream.

s390x appears to present two RNG interfaces: - a "TRNG" that gathers entropy using some hardware function; and - a "DRBG" that takes in a seed and expands it.

Previously, the TRNG was wired up to arch_get_random_{long,int}(), but it was observed that this was being called really frequently, resulting in high overhead. So it was changed to be wired up to arch_get_random_ seed_{long,int}(), which was a reasonable decision. Later on, the DRBG was then wired up to arch_get_random_{long,int}(), with a complicated buffer filling thread, to control overhead and rate.

Fortunately, none of the performance issues matter much now. The RNG always attempts to use arch_get_random_seed_{long,int}() first, which means a complicated implementation of arch_get_random_{long,int}() isn't really valuable or useful to have around. And it's only used when reseeding, which means it won't hit the high throughput complications that were faced before.

So this commit returns to an earlier design of just calling the TRNG in arch_get_random_seed_{long,int}(), and returning false in arch_get_ random_{long,int}().

Part of what makes the simplification possible is that the RNG now seeds itself using the TRNG at bootup. But this only works if the TRNG is detected early in boot, before random_init() is called. So this commit also causes that check to happen in setup_arch().

Cc: stable@vger.kernel.org Cc: Harald Freudenberger freude@linux.ibm.com Cc: Ingo Franzki ifranzki@linux.ibm.com Cc: Juergen Christ jchrist@linux.ibm.com Cc: Heiko Carstens hca@linux.ibm.com Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Link: https://lore.kernel.org/r/20220610222023.378448-1-Jason@zx2c4.com Reviewed-by: Harald Freudenberger freude@linux.ibm.com Acked-by: Heiko Carstens hca@linux.ibm.com Signed-off-by: Alexander Gordeev agordeev@linux.ibm.com Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com --- arch/s390/crypto/arch_random.c | 20 +++---------------- arch/s390/include/asm/archrandom.h | 32 +++++++++++++----------------- arch/s390/kernel/setup.c | 5 +++++ 3 files changed, 22 insertions(+), 35 deletions(-)

diff --git a/arch/s390/crypto/arch_random.c b/arch/s390/crypto/arch_random.c index 36aefc07d10c..1f2d40993c4d 100644 --- a/arch/s390/crypto/arch_random.c +++ b/arch/s390/crypto/arch_random.c @@ -1,13 +1,9 @@ +// SPDX-License-Identifier: GPL-2.0 /* * s390 arch random implementation. * - * Copyright IBM Corp. 2017 - * Author(s): Harald Freudenberger freude@de.ibm.com - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License (version 2 only) - * as published by the Free Software Foundation. - * + * Copyright IBM Corp. 2017, 2020 + * Author(s): Harald Freudenberger */

#include <linux/kernel.h> @@ -20,13 +16,3 @@ DEFINE_STATIC_KEY_FALSE(s390_arch_random_available);

atomic64_t s390_arch_random_counter = ATOMIC64_INIT(0); EXPORT_SYMBOL(s390_arch_random_counter); - -static int __init s390_arch_random_init(void) -{ - /* check if subfunction CPACF_PRNO_TRNG is available */ - if (cpacf_query_func(CPACF_PRNO, CPACF_PRNO_TRNG)) - static_branch_enable(&s390_arch_random_available); - - return 0; -} -arch_initcall(s390_arch_random_init); diff --git a/arch/s390/include/asm/archrandom.h b/arch/s390/include/asm/archrandom.h index ddf97715ee53..2c6e1c6ecbe7 100644 --- a/arch/s390/include/asm/archrandom.h +++ b/arch/s390/include/asm/archrandom.h @@ -2,7 +2,7 @@ /* * Kernel interface for the s390 arch_random_* functions * - * Copyright IBM Corp. 2017 + * Copyright IBM Corp. 2017, 2020 * * Author: Harald Freudenberger freude@de.ibm.com * @@ -20,38 +20,34 @@ DECLARE_STATIC_KEY_FALSE(s390_arch_random_available); extern atomic64_t s390_arch_random_counter;

-static void s390_arch_random_generate(u8 *buf, unsigned int nbytes) +static inline bool __must_check arch_get_random_long(unsigned long *v) { - cpacf_trng(NULL, 0, buf, nbytes); - atomic64_add(nbytes, &s390_arch_random_counter); + return false; }

-static inline bool arch_get_random_long(unsigned long *v) +static inline bool __must_check arch_get_random_int(unsigned int *v) { - if (static_branch_likely(&s390_arch_random_available)) { - s390_arch_random_generate((u8 *)v, sizeof(*v)); - return true; - } return false; }

-static inline bool arch_get_random_int(unsigned int *v) +static inline bool __must_check arch_get_random_seed_long(unsigned long *v) { if (static_branch_likely(&s390_arch_random_available)) { - s390_arch_random_generate((u8 *)v, sizeof(*v)); + cpacf_trng(NULL, 0, (u8 *)v, sizeof(*v)); + atomic64_add(sizeof(*v), &s390_arch_random_counter); return true; } return false; }

-static inline bool arch_get_random_seed_long(unsigned long *v) +static inline bool __must_check arch_get_random_seed_int(unsigned int *v) { - return arch_get_random_long(v); -} - -static inline bool arch_get_random_seed_int(unsigned int *v) -{ - return arch_get_random_int(v); + if (static_branch_likely(&s390_arch_random_available)) { + cpacf_trng(NULL, 0, (u8 *)v, sizeof(*v)); + atomic64_add(sizeof(*v), &s390_arch_random_counter); + return true; + } + return false; }

#endif /* CONFIG_ARCH_RANDOM */ diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c index e9ef093eb676..b3343f093f67 100644 --- a/arch/s390/kernel/setup.c +++ b/arch/s390/kernel/setup.c @@ -853,6 +853,11 @@ static void __init setup_randomness(void) if (stsi(vmms, 3, 2, 2) == 0 && vmms->count) add_device_randomness(&vmms->vm, sizeof(vmms->vm[0]) * vmms->count); memblock_free((unsigned long) vmms, PAGE_SIZE); + +#ifdef CONFIG_ARCH_RANDOM + if (cpacf_query_func(CPACF_PRNO, CPACF_PRNO_TRNG)) + static_branch_enable(&s390_arch_random_available); +#endif }

/*