s390/crypto: Provide s390 specific arch random functionality.

This patch introduces s390 specific arch random functionality.
There exists a generic kernel API for arch specific random
number implementation (see include/linux/random.h). Here
comes the header file and a very small static code part
implementing the arch_random_* API based on the TRNG
subfunction coming with the reworked PRNG instruction.

The arch random implementation hooks into the kernel
initialization and checks for availability of the TRNG
function. In accordance to the arch random API all functions
return false if the TRNG is not available. Otherwise the new
high quality entropy source provides fresh random on each
invocation.

The s390 arch random feature build is controlled via
CONFIG_ARCH_RANDOM. This config option located in
arch/s390/Kconfig is enabled by default and appears
as entry "s390 architectural random number generation API"
in the submenu "Processor type and features" for s390 builds.

Signed-off-by: Harald Freudenberger <freude@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

2 files changed, 32 insertions, 0 deletions

diff --git a/arch/s390/crypto/Makefile b/arch/s390/crypto/Makefile
index 402c530c6da5..678d9863e3f0 100644
--- a/arch/s390/crypto/Makefile
+++ b/arch/s390/crypto/Makefile
@@ -10,5 +10,6 @@ obj-$(CONFIG_CRYPTO_AES_S390) += aes_s390.o paes_s390.o
 obj-$(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
 
 crc32-vx_s390-y := crc32-vx.o crc32le-vx.o crc32be-vx.o
diff --git a/arch/s390/crypto/arch_random.c b/arch/s390/crypto/arch_random.c
new file mode 100644
index 000000000000..9317b3e645e2
--- /dev/null
+++ b/arch/s390/crypto/arch_random.c
@@ -0,0 +1,31 @@
+/*
+ * 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.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/atomic.h>
+#include <linux/static_key.h>
+#include <asm/cpacf.h>
+
+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);