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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: Torsten Duwe <duwe@suse.de> Signed-off-by: Theodore Ts'o <tytso@mit.edu> Acked-by: H. Peter Anvin <hpa@zytor.com>
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parent
c84dbf61a7
commit
be4000bc46
1 changed files with 64 additions and 5 deletions
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@ -38,6 +38,7 @@
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#include <linux/fs.h>
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#include <linux/sched.h>
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#include <linux/miscdevice.h>
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#include <linux/kthread.h>
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#include <linux/delay.h>
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#include <linux/slab.h>
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#include <linux/random.h>
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@ -50,10 +51,18 @@
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static struct hwrng *current_rng;
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static struct task_struct *hwrng_fill;
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static LIST_HEAD(rng_list);
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static DEFINE_MUTEX(rng_mutex);
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static int data_avail;
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static u8 *rng_buffer;
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static u8 *rng_buffer, *rng_fillbuf;
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static unsigned short current_quality = 700; /* an arbitrary 70% */
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module_param(current_quality, ushort, 0644);
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MODULE_PARM_DESC(current_quality,
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"current hwrng entropy estimation per mill");
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static void start_khwrngd(void);
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static size_t rng_buffer_size(void)
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{
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@ -62,9 +71,18 @@ static size_t rng_buffer_size(void)
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static inline int hwrng_init(struct hwrng *rng)
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{
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if (!rng->init)
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return 0;
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return rng->init(rng);
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int err;
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if (rng->init) {
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err = rng->init(rng);
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if (err)
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return err;
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}
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if (current_quality > 0 && !hwrng_fill)
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start_khwrngd();
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return 0;
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}
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static inline void hwrng_cleanup(struct hwrng *rng)
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@ -300,6 +318,36 @@ static int register_miscdev(void)
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goto out;
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}
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static int hwrng_fillfn(void *unused)
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{
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long rc;
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while (!kthread_should_stop()) {
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if (!current_rng)
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break;
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rc = rng_get_data(current_rng, rng_fillbuf,
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rng_buffer_size(), 1);
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if (rc <= 0) {
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pr_warn("hwrng: no data available\n");
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msleep_interruptible(10000);
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continue;
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}
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add_hwgenerator_randomness((void *)rng_fillbuf, rc,
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(rc*current_quality)>>10);
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}
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hwrng_fill = 0;
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return 0;
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}
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static void start_khwrngd(void)
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{
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hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
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if (hwrng_fill == ERR_PTR(-ENOMEM)) {
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pr_err("hwrng_fill thread creation failed");
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hwrng_fill = NULL;
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}
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}
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int hwrng_register(struct hwrng *rng)
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{
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int err = -EINVAL;
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@ -320,6 +368,13 @@ int hwrng_register(struct hwrng *rng)
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if (!rng_buffer)
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goto out_unlock;
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}
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if (!rng_fillbuf) {
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rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL);
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if (!rng_fillbuf) {
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kfree(rng_buffer);
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goto out_unlock;
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}
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}
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/* Must not register two RNGs with the same name. */
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err = -EEXIST;
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@ -375,8 +430,11 @@ void hwrng_unregister(struct hwrng *rng)
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current_rng = NULL;
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}
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}
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if (list_empty(&rng_list))
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if (list_empty(&rng_list)) {
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unregister_miscdev();
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if (hwrng_fill)
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kthread_stop(hwrng_fill);
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}
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mutex_unlock(&rng_mutex);
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}
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@ -387,6 +445,7 @@ static void __exit hwrng_exit(void)
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mutex_lock(&rng_mutex);
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BUG_ON(current_rng);
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kfree(rng_buffer);
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kfree(rng_fillbuf);
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mutex_unlock(&rng_mutex);
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}
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