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random: add a switch of using rdrand ins in _extract_crng 

on some old AMD CPU(eg: older then AMD EPYC 7K62) , rdrand is slowly,
random using rdrand to make the random num more hard to be guessed.
while the randomness is not really affect by rdrand.

when user not using random for security case, (eg: just geting some
random num, not using it to generate password) using rdrand on old
amd processor is so expensive.

so, add a swith to rdrand, by default using the rdrand, when closed
using tsc, jiffies, and entropy from the fast_pool to emulate the rdrand

testing on AMD EPYC 7K62 like follow:

---

echo 1 > /proc/sys/kernel/random/tos_use_rdrand
stress-ng --urandom 2 --timeout 10s --times --metrics
bogo ops real time  usr time  sys time   bogo ops/s   bogo ops/s
           (secs)    (secs)    (secs)   (real time) (usr+sys time)
   16542     10.00      0.00     19.98      1654.09       827.93

---

echo 0 > /proc/sys/kernel/random/tos_use_rdrand
stress-ng --urandom 2 --timeout 10s --times --metrics
bogo ops real time  usr time  sys time   bogo ops/s   bogo ops/s
           (secs)    (secs)    (secs)   (real time) (usr+sys time)
  222005     10.00      0.05     19.93     22200.41     11111.36

/dev/urandom reading and geturandom  syscall 13 times faster then using
really rdrand.

Signed-off-by: mengensun <mengensun@tencent.com>
Reviewed-by: frankjpliu <frankjpliu@tencent.com>
Reviewed-by: anakinzhang <anakinzhang@tencent.com>
Reviewed-by: Ruippan <Ruippan@tencent.com>
This commit is contained in:
mengensun 2022-05-09 11:24:07 +08:00
parent d02bb084f2
commit ace0b7c6ac
1 changed files with 36 additions and 1 deletions
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37
drivers/char/random.c
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@ -514,6 +514,9 @@ static struct ratelimit_state urandom_warning =
static int ratelimit_disable __read_mostly;
static int use_rdrand = 1;
static unsigned long simulation_rdrand(void);
module_param_named(ratelimit_disable, ratelimit_disable, int, 0644);
MODULE_PARM_DESC(ratelimit_disable, "Disable random ratelimit suppression");
@ -1048,6 +1051,7 @@ static void crng_reseed(struct crng_state *crng, struct entropy_store *r)
}
}
static void _extract_crng(struct crng_state *crng,
__u8 out[CHACHA_BLOCK_SIZE])
{
@ -1057,9 +1061,16 @@ static void _extract_crng(struct crng_state *crng,
(time_after(crng_global_init_time, crng->init_time) ||
time_after(jiffies, crng->init_time + CRNG_RESEED_INTERVAL)))
crng_reseed(crng, crng == &primary_crng ? &input_pool : NULL);
spin_lock_irqsave(&crng->lock, flags);
if (arch_get_random_long(&v))
/* primary_crng is seldomly extracted */
if (!use_rdrand && crng != &primary_crng) {
v = simulation_rdrand();
crng->state[14] ^= v;
} else if (arch_get_random_long(&v)) {
crng->state[14] ^= v;
}
chacha20_block(&crng->state[0], out);
if (crng->state[12] == 0)
crng->state[13]++;
@ -1268,6 +1279,21 @@ void add_input_randomness(unsigned int type, unsigned int code,
EXPORT_SYMBOL_GPL(add_input_randomness);
static DEFINE_PER_CPU(struct fast_pool, irq_randomness);
static unsigned long simulation_rdrand()
{
unsigned long entropy;
struct fast_pool *fast_pool;
entropy = random_get_entropy();
fast_pool = this_cpu_ptr(&irq_randomness);
entropy ^= fast_pool->pool[0];
entropy ^= fast_pool->pool[1];
entropy ^= fast_pool->pool[2];
entropy ^= fast_pool->pool[3];
entropy ^= jiffies;
return entropy;
}
#ifdef ADD_INTERRUPT_BENCH
static unsigned long avg_cycles, avg_deviation;
@ -2327,6 +2353,15 @@ struct ctl_table random_table[] = {
.mode = 0444,
.proc_handler = proc_do_uuid,
},
{
.procname = "tos_use_rdrand",
.data = &use_rdrand,
.maxlen = sizeof(use_rdrand),
.mode = 0644,
.proc_handler = proc_dointvec_minmax,
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_ONE
},
#ifdef ADD_INTERRUPT_BENCH
{
.procname = "add_interrupt_avg_cycles",