path: root/arch/s390/include/asm/archrandom.h
diff options
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/s390/include/asm/archrandom.h
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/s390/include/asm/archrandom.h')
1 files changed, 4 insertions, 1 deletions
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 @@
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;

Privacy Policy