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authorHarald Freudenberger <freude@linux.ibm.com>2020-12-03 15:02:08 +0100
committerHeiko Carstens <hca@linux.ibm.com>2020-12-10 21:02:08 +0100
commitff98cc986ae883eec5f26af72d4e2406612fe683 (patch)
tree4147384f12a514c0935ca76da34c94f8f2ff7b1a /arch
parentb5e438ebd7e808d1d2435159ac4742e01a94b8da (diff)
s390/crypto: add arch_get_random_long() support
The random longs to be pulled by arch_get_random_long() are prepared in an 4K buffer which is filled from the NIST 800-90 compliant s390 drbg. By default the random long buffer is refilled 256 times before the drbg itself needs a reseed. The reseed of the drbg is done with 32 bytes fetched from the high quality (but slow) trng which is assumed to deliver 100% entropy. So the 32 * 8 = 256 bits of entropy are spread over 256 * 4KB = 1MB serving 131072 arch_get_random_long() invocations before reseeded. How often the 4K random long buffer is refilled with the drbg before the drbg is reseeded can be adjusted. There is a module parameter 's390_arch_rnd_long_drbg_reseed' accessible via /sys/module/arch_random/parameters/rndlong_drbg_reseed or as kernel command line parameter arch_random.rndlong_drbg_reseed=<value> This parameter tells how often the drbg fills the 4K buffer before it is re-seeded by fresh entropy from the trng. A value of 16 results in reseeding the drbg at every 16 * 4 KB = 64 KB with 32 bytes of fresh entropy pulled from the trng. So a value of 16 would result in 256 bits entropy per 64 KB. A value of 256 results in 1MB of drbg output before a reseed of the drbg is done. So this would spread the 256 bits of entropy among 1MB. Setting this parameter to 0 forces the reseed to take place every time the 4K buffer is depleted, so the entropy rises to 256 bits entropy per 4K or 0.5 bit entropy per arch_get_random_long(). With setting this parameter to negative values all this effort is disabled, arch_get_random long() returns false and thus indicating that the arch_get_random_long() feature is disabled at all. arch_get_random_long() is used by random.c among others to provide an initial hash value to be mixed with the entropy pool on every random data pull. For about 64 bytes read from /dev/urandom there is one call to arch_get_random_long(). So these additional random long values count for performance of /dev/urandom with measurable but low penalty. Signed-off-by: Harald Freudenberger <freude@linux.ibm.com> Reviewed-by: Ingo Franzki <ifranzki@linux.ibm.com> Reviewed-by: Juergen Christ <jchrist@linux.ibm.com> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Diffstat (limited to 'arch')
-rw-r--r--arch/s390/crypto/arch_random.c110
-rw-r--r--arch/s390/include/asm/archrandom.h5
2 files changed, 113 insertions, 2 deletions
diff --git a/arch/s390/crypto/arch_random.c b/arch/s390/crypto/arch_random.c
index dd95cdbd22ce..7b947728d57e 100644
--- a/arch/s390/crypto/arch_random.c
+++ b/arch/s390/crypto/arch_random.c
@@ -2,7 +2,7 @@
/*
* s390 arch random implementation.
*
- * Copyright IBM Corp. 2017, 2018
+ * Copyright IBM Corp. 2017, 2020
* Author(s): Harald Freudenberger
*
* The s390_arch_random_generate() function may be called from random.c
@@ -33,6 +33,7 @@
#include <linux/slab.h>
#include <linux/static_key.h>
#include <linux/workqueue.h>
+#include <linux/moduleparam.h>
#include <asm/cpacf.h>
DEFINE_STATIC_KEY_FALSE(s390_arch_random_available);
@@ -99,6 +100,113 @@ static void arch_rng_refill_buffer(struct work_struct *unused)
queue_delayed_work(system_long_wq, &arch_rng_work, delay);
}
+/*
+ * Here follows the implementation of s390_arch_get_random_long().
+ *
+ * The random longs to be pulled by arch_get_random_long() are
+ * prepared in an 4K buffer which is filled from the NIST 800-90
+ * compliant s390 drbg. By default the random long buffer is refilled
+ * 256 times before the drbg itself needs a reseed. The reseed of the
+ * drbg is done with 32 bytes fetched from the high quality (but slow)
+ * trng which is assumed to deliver 100% entropy. So the 32 * 8 = 256
+ * bits of entropy are spread over 256 * 4KB = 1MB serving 131072
+ * arch_get_random_long() invocations before reseeded.
+ *
+ * How often the 4K random long buffer is refilled with the drbg
+ * before the drbg is reseeded can be adjusted. There is a module
+ * parameter 's390_arch_rnd_long_drbg_reseed' accessible via
+ * /sys/module/arch_random/parameters/rndlong_drbg_reseed
+ * or as kernel command line parameter
+ * arch_random.rndlong_drbg_reseed=<value>
+ * This parameter tells how often the drbg fills the 4K buffer before
+ * it is re-seeded by fresh entropy from the trng.
+ * A value of 16 results in reseeding the drbg at every 16 * 4 KB = 64
+ * KB with 32 bytes of fresh entropy pulled from the trng. So a value
+ * of 16 would result in 256 bits entropy per 64 KB.
+ * A value of 256 results in 1MB of drbg output before a reseed of the
+ * drbg is done. So this would spread the 256 bits of entropy among 1MB.
+ * Setting this parameter to 0 forces the reseed to take place every
+ * time the 4K buffer is depleted, so the entropy rises to 256 bits
+ * entropy per 4K or 0.5 bit entropy per arch_get_random_long(). With
+ * setting this parameter to negative values all this effort is
+ * disabled, arch_get_random long() returns false and thus indicating
+ * that the arch_get_random_long() feature is disabled at all.
+ */
+
+static unsigned long rndlong_buf[512];
+static DEFINE_SPINLOCK(rndlong_lock);
+static int rndlong_buf_index;
+
+static int rndlong_drbg_reseed = 256;
+module_param_named(rndlong_drbg_reseed, rndlong_drbg_reseed, int, 0600);
+MODULE_PARM_DESC(rndlong_drbg_reseed, "s390 arch_get_random_long() drbg reseed");
+
+static inline void refill_rndlong_buf(void)
+{
+ static u8 prng_ws[240];
+ static int drbg_counter;
+
+ if (--drbg_counter < 0) {
+ /* need to re-seed the drbg */
+ u8 seed[32];
+
+ /* fetch seed from trng */
+ cpacf_trng(NULL, 0, seed, sizeof(seed));
+ /* seed drbg */
+ memset(prng_ws, 0, sizeof(prng_ws));
+ cpacf_prno(CPACF_PRNO_SHA512_DRNG_SEED,
+ &prng_ws, NULL, 0, seed, sizeof(seed));
+ /* re-init counter for drbg */
+ drbg_counter = rndlong_drbg_reseed;
+ }
+
+ /* fill the arch_get_random_long buffer from drbg */
+ cpacf_prno(CPACF_PRNO_SHA512_DRNG_GEN, &prng_ws,
+ (u8 *) rndlong_buf, sizeof(rndlong_buf),
+ NULL, 0);
+}
+
+bool s390_arch_get_random_long(unsigned long *v)
+{
+ bool rc = false;
+ unsigned long flags;
+
+ /* arch_get_random_long() disabled ? */
+ if (rndlong_drbg_reseed < 0)
+ return false;
+
+ /* try to lock the random long lock */
+ if (!spin_trylock_irqsave(&rndlong_lock, flags))
+ return false;
+
+ if (--rndlong_buf_index >= 0) {
+ /* deliver next long value from the buffer */
+ *v = rndlong_buf[rndlong_buf_index];
+ rc = true;
+ goto out;
+ }
+
+ /* buffer is depleted and needs refill */
+ if (in_interrupt()) {
+ /* delay refill in interrupt context to next caller */
+ rndlong_buf_index = 0;
+ goto out;
+ }
+
+ /* refill random long buffer */
+ refill_rndlong_buf();
+ rndlong_buf_index = ARRAY_SIZE(rndlong_buf);
+
+ /* and provide one random long */
+ *v = rndlong_buf[--rndlong_buf_index];
+ rc = true;
+
+out:
+ spin_unlock_irqrestore(&rndlong_lock, flags);
+ return rc;
+}
+EXPORT_SYMBOL(s390_arch_get_random_long);
+
static int __init s390_arch_random_init(void)
{
/* all the needed PRNO subfunctions available ? */
diff --git a/arch/s390/include/asm/archrandom.h b/arch/s390/include/asm/archrandom.h
index de61ce562052..5dc712fde3c7 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>
*
@@ -19,10 +19,13 @@
DECLARE_STATIC_KEY_FALSE(s390_arch_random_available);
extern atomic64_t s390_arch_random_counter;
+bool s390_arch_get_random_long(unsigned long *v);
bool s390_arch_random_generate(u8 *buf, unsigned int nbytes);
static inline bool __must_check arch_get_random_long(unsigned long *v)
{
+ if (static_branch_likely(&s390_arch_random_available))
+ return s390_arch_get_random_long(v);
return false;
}

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