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hwrng: create filler thread

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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: Torsten Duwe <duwe@suse.de>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Acked-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
Torsten Duwe 2014-06-14 23:46:03 -04:00 committed by Theodore Ts'o
parent c84dbf61a7
commit be4000bc46
1 changed files with 64 additions and 5 deletions
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69
drivers/char/hw_random/core.c
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@ -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)
return 0;
return rng->init(rng);
int err;
if (rng->init) {
err = rng->init(rng);
if (err)
return err;
}
if (current_quality > 0 && !hwrng_fill)
start_khwrngd();
return 0;
}
static inline void hwrng_cleanup(struct hwrng *rng)
@ -300,6 +318,36 @@ err_misc_dereg:
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);
}