diff options
Diffstat (limited to 'arch/s390/crypto/arch_random.c')
| -rw-r--r-- | arch/s390/crypto/arch_random.c | 110 |
1 files changed, 109 insertions, 1 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 ? */ |