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Commit be4000bc authored by Torsten Duwe's avatar Torsten Duwe Committed by Theodore Ts'o
Browse files

hwrng: create filler thread 



This can be viewed as the in-kernel equivalent of hwrngd;
like FUSE it is a good thing to have a mechanism in user land,
but for some reasons (simplicity, secrecy, integrity, speed)
it may be better to have it in kernel space.

This patch creates a thread once a hwrng registers, and uses
the previously established add_hwgenerator_randomness() to feed
its data to the input pool as long as needed. A derating factor
is used to bias the entropy estimation and to disable this
mechanism entirely when set to zero.

Signed-off-by: default avatarTorsten Duwe <duwe@suse.de>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Acked-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent c84dbf61

drivers/char/hw_random/core.c

+64 −5
Original line number Diff line number Diff line
@@ -38,6 +38,7 @@ 
#include <linux/fs.h>

#include <linux/sched.h>

#include <linux/miscdevice.h>

#include <linux/kthread.h>

#include <linux/delay.h>

#include <linux/slab.h>

#include <linux/random.h>
@@ -50,10 +51,18 @@ 




static struct hwrng *current_rng;

static struct task_struct *hwrng_fill;

static LIST_HEAD(rng_list);

static DEFINE_MUTEX(rng_mutex);

static int data_avail;

static u8 *rng_buffer;

static u8 *rng_buffer, *rng_fillbuf;

static unsigned short current_quality = 700; /* an arbitrary 70% */



module_param(current_quality, ushort, 0644);

MODULE_PARM_DESC(current_quality,

		 "current hwrng entropy estimation per mill");



static void start_khwrngd(void);



static size_t rng_buffer_size(void)

{
@@ -62,9 +71,18 @@ static size_t rng_buffer_size(void) 


static inline int hwrng_init(struct hwrng *rng)

{

	if (!rng->init)

	int err;



	if (rng->init) {

		err = rng->init(rng);

		if (err)

			return err;

	}



	if (current_quality > 0 && !hwrng_fill)

		start_khwrngd();



	return 0;

	return rng->init(rng);

}



static inline void hwrng_cleanup(struct hwrng *rng)
@@ -300,6 +318,36 @@ static int register_miscdev(void) 
	goto out;

}



static int hwrng_fillfn(void *unused)

{

	long rc;



	while (!kthread_should_stop()) {

		if (!current_rng)

			break;

		rc = rng_get_data(current_rng, rng_fillbuf,

				  rng_buffer_size(), 1);

		if (rc <= 0) {

			pr_warn("hwrng: no data available\n");

			msleep_interruptible(10000);

			continue;

		}

		add_hwgenerator_randomness((void *)rng_fillbuf, rc,

					   (rc*current_quality)>>10);

	}

	hwrng_fill = 0;

	return 0;

}



static void start_khwrngd(void)

{

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

	if (hwrng_fill == ERR_PTR(-ENOMEM)) {

		pr_err("hwrng_fill thread creation failed");

		hwrng_fill = NULL;

	}

}



int hwrng_register(struct hwrng *rng)

{

	int err = -EINVAL;
@@ -320,6 +368,13 @@ int hwrng_register(struct hwrng *rng) 
		if (!rng_buffer)

			goto out_unlock;

	}

	if (!rng_fillbuf) {

		rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL);

		if (!rng_fillbuf) {

			kfree(rng_buffer);

			goto out_unlock;

		}

	}



	/* Must not register two RNGs with the same name. */

	err = -EEXIST;
@@ -375,8 +430,11 @@ void hwrng_unregister(struct hwrng *rng) 
				current_rng = NULL;

		}

	}

	if (list_empty(&rng_list))

	if (list_empty(&rng_list)) {

		unregister_miscdev();

		if (hwrng_fill)

			kthread_stop(hwrng_fill);

	}



	mutex_unlock(&rng_mutex);

}
@@ -387,6 +445,7 @@ static void __exit hwrng_exit(void) 
	mutex_lock(&rng_mutex);

	BUG_ON(current_rng);

	kfree(rng_buffer);

	kfree(rng_fillbuf);

	mutex_unlock(&rng_mutex);

}