Hello
I am writing the PRNG driver for the Allwinner Security System SoC A20.
I didn't know how to test it, so I have found that char/hw_random/exynos-rng.c
exposes a PRNG via the hwrng interfaces.
So I have written a HWRNG driver that use the SS PRNG via the crypto API
(crypto_alloc_rng/crypto_rng_reset/crypto_rng_get_bytes)
I have attached the code in case of...
The problem is that rngtest show some failures.
cat /dev/hwrng | rngtest
rngtest: bits received from input: 1876960032
rngtest: FIPS 140-2 successes: 93771
rngtest: FIPS 140-2 failures: 77
rngtest: FIPS 140-2(2001-10-10) Monobit: 15
rngtest: FIPS 140-2(2001-10-10) Poker: 11
rngtest: FIPS 140-2(2001-10-10) Runs: 30
rngtest: FIPS 140-2(2001-10-10) Long run: 22
rngtest: FIPS 140-2(2001-10-10) Continuous run: 0
rngtest: input channel speed: (min=979.894; avg=109756.722;
max=4882812.500)Kibits/s
rngtest: FIPS tests speed: (min=1.309; avg=32.191; max=39.986)Mibits/s
rngtest: Program run time: 72523286 microseconds
So I have questions:
- Does the use of a HWRNG driver for exposing the PRNG is a good idea ?
- Could I think the PRNG is good enough with the result of rngtest ?
Bests regards
/*
* ss-rng.c - Random Number Generator driver for the Security System
*/
#include <linux/hw_random.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <crypto/rng.h>
struct ss_rng_ctx {
struct hwrng rng;
struct crypto_rng *cr;
};
static struct ss_rng_ctx ss_rng;
#define SS_SEED_LEN (192/8)
static int ss_rng_init(struct hwrng *rng)
{
int i;
u8 seed[SS_SEED_LEN];
u32 *s = (u32 *)seed;
for (i = 0 ; i < SS_SEED_LEN/4 ; i++)
s[i] = jiffies;
crypto_rng_reset(ss_rng.cr, seed, SS_SEED_LEN);
return 0;
}
static int ss_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
{
return crypto_rng_get_bytes(ss_rng.cr, buf, max);
}
static int ss_rng_probe(void)
{
int err;
struct crypto_rng *rng;
const char *name;
rng = crypto_alloc_rng("stdrng", 0, 0);
err = PTR_ERR(rng);
if (IS_ERR(rng))
return err;
name = crypto_tfm_alg_driver_name(crypto_rng_tfm(rng));
if (strcmp(name, "rng-sunxi-ss") != 0) {
pr_err("ERROR: Cannot get Security System PRNG, but got %s
instead\n", name);
crypto_free_rng(rng);
return -ENODEV;
}
ss_rng.cr = rng;
ss_rng.rng.name = "Security System HWRNG";
ss_rng.rng.init = ss_rng_init;
ss_rng.rng.read = ss_rng_read;
err = hwrng_register(&ss_rng.rng);
if (err != 0) {
crypto_free_rng(ss_rng.cr);
}
return err;
}
static void ss_rng_remove(void)
{
hwrng_unregister(&ss_rng.rng);
crypto_free_rng(ss_rng.cr);
}
module_init(ss_rng_probe);
module_exit(ss_rng_remove);
MODULE_DESCRIPTION("Allwinner Security System H/W Random Number Generator
driver");
MODULE_AUTHOR("Corentin LABBE <clabbe.montj...@gmail.com>");
MODULE_LICENSE("GPL");
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