*
* Copyright IBM Corp. 2017, 2020
* Author(s): Harald Freudenberger
- *
- * The s390_arch_random_generate() function may be called from random.c
- * in interrupt context. So this implementation does the best to be very
- * fast. There is a buffer of random data which is asynchronously checked
- * and filled by a workqueue thread.
- * If there are enough bytes in the buffer the s390_arch_random_generate()
- * just delivers these bytes. Otherwise false is returned until the
- * worker thread refills the buffer.
- * The worker fills the rng buffer by pulling fresh entropy from the
- * high quality (but slow) true hardware random generator. This entropy
- * is then spread over the buffer with an pseudo random generator PRNG.
- * As the arch_get_random_seed_long() fetches 8 bytes and the calling
- * function add_interrupt_randomness() counts this as 1 bit entropy the
- * distribution needs to make sure there is in fact 1 bit entropy contained
- * in 8 bytes of the buffer. The current values pull 32 byte entropy
- * and scatter this into a 2048 byte buffer. So 8 byte in the buffer
- * will contain 1 bit of entropy.
- * The worker thread is rescheduled based on the charge level of the
- * buffer but at least with 500 ms delay to avoid too much CPU consumption.
- * So the max. amount of rng data delivered via arch_get_random_seed is
- * limited to 4k bytes per second.
*/
#include <linux/kernel.h>
#include <linux/atomic.h>
#include <linux/random.h>
-#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);
atomic64_t s390_arch_random_counter = ATOMIC64_INIT(0);
EXPORT_SYMBOL(s390_arch_random_counter);
-
-#define ARCH_REFILL_TICKS (HZ/2)
-#define ARCH_PRNG_SEED_SIZE 32
-#define ARCH_RNG_BUF_SIZE 2048
-
-static DEFINE_SPINLOCK(arch_rng_lock);
-static u8 *arch_rng_buf;
-static unsigned int arch_rng_buf_idx;
-
-static void arch_rng_refill_buffer(struct work_struct *);
-static DECLARE_DELAYED_WORK(arch_rng_work, arch_rng_refill_buffer);
-
-bool s390_arch_random_generate(u8 *buf, unsigned int nbytes)
-{
- /* max hunk is ARCH_RNG_BUF_SIZE */
- if (nbytes > ARCH_RNG_BUF_SIZE)
- return false;
-
- /* lock rng buffer */
- if (!spin_trylock(&arch_rng_lock))
- return false;
-
- /* try to resolve the requested amount of bytes from the buffer */
- arch_rng_buf_idx -= nbytes;
- if (arch_rng_buf_idx < ARCH_RNG_BUF_SIZE) {
- memcpy(buf, arch_rng_buf + arch_rng_buf_idx, nbytes);
- atomic64_add(nbytes, &s390_arch_random_counter);
- spin_unlock(&arch_rng_lock);
- return true;
- }
-
- /* not enough bytes in rng buffer, refill is done asynchronously */
- spin_unlock(&arch_rng_lock);
-
- return false;
-}
-EXPORT_SYMBOL(s390_arch_random_generate);
-
-static void arch_rng_refill_buffer(struct work_struct *unused)
-{
- unsigned int delay = ARCH_REFILL_TICKS;
-
- spin_lock(&arch_rng_lock);
- if (arch_rng_buf_idx > ARCH_RNG_BUF_SIZE) {
- /* buffer is exhausted and needs refill */
- u8 seed[ARCH_PRNG_SEED_SIZE];
- u8 prng_wa[240];
- /* fetch ARCH_PRNG_SEED_SIZE bytes of entropy */
- cpacf_trng(NULL, 0, seed, sizeof(seed));
- /* blow this entropy up to ARCH_RNG_BUF_SIZE with PRNG */
- memset(prng_wa, 0, sizeof(prng_wa));
- cpacf_prno(CPACF_PRNO_SHA512_DRNG_SEED,
- &prng_wa, NULL, 0, seed, sizeof(seed));
- cpacf_prno(CPACF_PRNO_SHA512_DRNG_GEN,
- &prng_wa, arch_rng_buf, ARCH_RNG_BUF_SIZE, NULL, 0);
- arch_rng_buf_idx = ARCH_RNG_BUF_SIZE;
- }
- delay += (ARCH_REFILL_TICKS * arch_rng_buf_idx) / ARCH_RNG_BUF_SIZE;
- spin_unlock(&arch_rng_lock);
-
- /* kick next check */
- 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 ? */
- if (cpacf_query_func(CPACF_PRNO, CPACF_PRNO_TRNG) &&
- cpacf_query_func(CPACF_PRNO, CPACF_PRNO_SHA512_DRNG_GEN)) {
-
- /* alloc arch random working buffer */
- arch_rng_buf = kmalloc(ARCH_RNG_BUF_SIZE, GFP_KERNEL);
- if (!arch_rng_buf)
- return -ENOMEM;
-
- /* kick worker queue job to fill the random buffer */
- queue_delayed_work(system_long_wq,
- &arch_rng_work, ARCH_REFILL_TICKS);
-
- /* enable arch random to the outside world */
- static_branch_enable(&s390_arch_random_available);
- }
-
- return 0;
-}
-arch_initcall(s390_arch_random_init);
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