Commit 67ec8cdf authored by Herbert Xu's avatar Herbert Xu
Browse files

hwrng: core - Remove add_early_randomness 

A potential deadlock was reported with the config file at

https://web.archive.org/web/20240522052129/https://0x0.st/XPN_.txt



In this particular configuration, the deadlock doesn't exist because
the warning triggered at a point before modules were even available.
However, the deadlock can be real because any module loaded would
invoke async_synchronize_full.

The issue is spurious for software crypto algorithms which aren't
themselves involved in async probing.  However, it would be hard to
avoid for a PCI crypto driver using async probing.

In this particular call trace, the problem is easily avoided because
the only reason the module is being requested during probing is the
add_early_randomness call in the hwrng core.  This feature is
vestigial since there is now a kernel thread dedicated to doing
exactly this.

So remove add_early_randomness as it is no longer needed.

Reported-by: default avatarNícolas F. R. A. Prado <nfraprado@collabora.com>
Reported-by: default avatarEric Biggers <ebiggers@kernel.org>
Fixes: 1b6d7f9e ("tpm: add session encryption protection to tpm2_get_random()")
Link: https://lore.kernel.org/r/119dc5ed-f159-41be-9dda-1a056f29888d@notapiano/


Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: default avatarJarkko Sakkinen <jarkko@kernel.org>
Tested-by: default avatarNícolas F. R. A. Prado <nfraprado@collabora.com>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
parent c6ab5c91

drivers/char/hw_random/core.c

+4 −43
Original line number Diff line number Diff line
@@ -64,19 +64,6 @@ static size_t rng_buffer_size(void) 
	return RNG_BUFFER_SIZE;

}



static void add_early_randomness(struct hwrng *rng)

{

	int bytes_read;



	mutex_lock(&reading_mutex);

	bytes_read = rng_get_data(rng, rng_fillbuf, 32, 0);

	mutex_unlock(&reading_mutex);

	if (bytes_read > 0) {

		size_t entropy = bytes_read * 8 * rng->quality / 1024;

		add_hwgenerator_randomness(rng_fillbuf, bytes_read, entropy, false);

	}

}



static inline void cleanup_rng(struct kref *kref)

{

	struct hwrng *rng = container_of(kref, struct hwrng, ref);
@@ -340,13 +327,12 @@ static ssize_t rng_current_store(struct device *dev, 
				 const char *buf, size_t len)

{

	int err;

	struct hwrng *rng, *old_rng, *new_rng;

	struct hwrng *rng, *new_rng;



	err = mutex_lock_interruptible(&rng_mutex);

	if (err)

		return -ERESTARTSYS;



	old_rng = current_rng;

	if (sysfs_streq(buf, "")) {

		err = enable_best_rng();

	} else {
@@ -362,11 +348,8 @@ static ssize_t rng_current_store(struct device *dev, 
	new_rng = get_current_rng_nolock();

	mutex_unlock(&rng_mutex);



	if (new_rng) {

		if (new_rng != old_rng)

			add_early_randomness(new_rng);

	if (new_rng)

		put_rng(new_rng);

	}



	return err ? : len;

}
@@ -544,7 +527,6 @@ int hwrng_register(struct hwrng *rng) 
{

	int err = -EINVAL;

	struct hwrng *tmp;

	bool is_new_current = false;



	if (!rng->name || (!rng->data_read && !rng->read))

		goto out;
@@ -573,25 +555,8 @@ int hwrng_register(struct hwrng *rng) 
		err = set_current_rng(rng);

		if (err)

			goto out_unlock;

		/* to use current_rng in add_early_randomness() we need

		 * to take a ref

		 */

		is_new_current = true;

		kref_get(&rng->ref);

	}

	mutex_unlock(&rng_mutex);

	if (is_new_current || !rng->init) {

		/*

		 * Use a new device's input to add some randomness to

		 * the system.  If this rng device isn't going to be

		 * used right away, its init function hasn't been

		 * called yet by set_current_rng(); so only use the

		 * randomness from devices that don't need an init callback

		 */

		add_early_randomness(rng);

	}

	if (is_new_current)

		put_rng(rng);

	return 0;

out_unlock:

	mutex_unlock(&rng_mutex);
@@ -602,12 +567,11 @@ EXPORT_SYMBOL_GPL(hwrng_register); 


void hwrng_unregister(struct hwrng *rng)

{

	struct hwrng *old_rng, *new_rng;

	struct hwrng *new_rng;

	int err;



	mutex_lock(&rng_mutex);



	old_rng = current_rng;

	list_del(&rng->list);

	complete_all(&rng->dying);

	if (current_rng == rng) {
@@ -626,11 +590,8 @@ void hwrng_unregister(struct hwrng *rng) 
	} else

		mutex_unlock(&rng_mutex);



	if (new_rng) {

		if (old_rng != new_rng)

			add_early_randomness(new_rng);

	if (new_rng)

		put_rng(new_rng);

	}



	wait_for_completion(&rng->cleanup_done);

}