Commit b006c439 authored by Dominik Brodowski's avatar Dominik Brodowski Committed by Herbert Xu
Browse files

hwrng: core - start hwrng kthread also for untrusted sources 



Start the hwrng kthread even if the hwrng source has a quality setting
of zero. Then, every crng reseed interval, one batch of data from this
zero-quality hwrng source will be mixed into the CRNG pool.

This patch is based on the assumption that data from a hwrng source
will not actively harm the CRNG state. Instead, many hwrng sources
(such as TPM devices), even though they are assigend a quality level of
zero, actually provide some entropy, which is good enough to mix into
the CRNG pool every once in a while.

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: default avatarDominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent 4edff849

drivers/char/hw_random/core.c

+10 −26
Original line number Diff line number Diff line
@@ -52,7 +52,7 @@ MODULE_PARM_DESC(default_quality, 


static void drop_current_rng(void);

static int hwrng_init(struct hwrng *rng);

static void hwrng_manage_rngd(struct hwrng *rng);

static int hwrng_fillfn(void *unused);



static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,

			       int wait);
@@ -96,6 +96,15 @@ static int set_current_rng(struct hwrng *rng) 
	drop_current_rng();

	current_rng = rng;



	/* if necessary, start hwrng thread */

	if (!hwrng_fill) {

		hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");

		if (IS_ERR(hwrng_fill)) {

			pr_err("hwrng_fill thread creation failed\n");

			hwrng_fill = NULL;

		}

	}



	return 0;

}
@@ -167,8 +176,6 @@ static int hwrng_init(struct hwrng *rng) 
		rng->quality = 1024;

	current_quality = rng->quality; /* obsolete */



	hwrng_manage_rngd(rng);



	return 0;

}
@@ -454,10 +461,6 @@ static ssize_t rng_quality_store(struct device *dev, 
	/* the best available RNG may have changed */

	ret = enable_best_rng();



	/* start/stop rngd if necessary */

	if (current_rng)

		hwrng_manage_rngd(current_rng);



out:

	mutex_unlock(&rng_mutex);

	return ret ? ret : len;
@@ -513,9 +516,6 @@ static int hwrng_fillfn(void *unused) 


		put_rng(rng);



		if (!quality)

			break;



		if (rc <= 0)

			continue;
@@ -534,22 +534,6 @@ static int hwrng_fillfn(void *unused) 
	return 0;

}



static void hwrng_manage_rngd(struct hwrng *rng)

{

	if (WARN_ON(!mutex_is_locked(&rng_mutex)))

		return;



	if (rng->quality == 0 && hwrng_fill)

		kthread_stop(hwrng_fill);

	if (rng->quality > 0 && !hwrng_fill) {

		hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");

		if (IS_ERR(hwrng_fill)) {

			pr_err("hwrng_fill thread creation failed\n");

			hwrng_fill = NULL;

		}

	}

}



int hwrng_register(struct hwrng *rng)

{

	int err = -EINVAL;