Some RNG devices may not be ready to give early randomness at probe()
time, and hence lose out on the opportunity to contribute to system
randomness at boot- or device hotplug- time.
This commit schedules a delayed work item for such devices, and fetches
early randomness after a delay. Currently the delay is 500ms, which is
enough for the lone device that needs such treatment: virtio-rng.
CC: Kees Cook <keescook@xxxxxxxxxxxx>
CC: Jason Cooper <jason@xxxxxxxxxxxxxx>
CC: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Amit Shah <amit.shah@xxxxxxxxxx>
---
drivers/char/hw_random/core.c | 20 +++++++++++++++++++-
include/linux/hw_random.h | 8 ++++++++
2 files changed, 27 insertions(+), 1 deletion(-)
diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index c4419ea..2a765fd 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -63,7 +63,7 @@ static size_t rng_buffer_size(void)
return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES;
}
-static void add_early_randomness(struct hwrng *rng)
+static void get_early_randomness(struct hwrng *rng)
{
unsigned char bytes[16];
int bytes_read;
@@ -79,6 +79,21 @@ static void add_early_randomness(struct hwrng *rng)
add_device_randomness(bytes, bytes_read);
}
+static void sched_init_random(struct work_struct *work)
+{
+ struct hwrng *rng = container_of(work, struct hwrng, dwork.work);
+
+ get_early_randomness(rng);
+}
+
+static void add_early_randomness(struct hwrng *rng)
+{
+ if (!(rng->flags & HWRNG_DELAY_READ_AT_INIT))
+ return get_early_randomness(rng);
+
+ schedule_delayed_work(&rng->dwork, msecs_to_jiffies(500));
+}
+
static inline int hwrng_init(struct hwrng *rng)
{
if (rng->init) {
@@ -351,6 +366,7 @@ int hwrng_register(struct hwrng *rng)
goto out_unlock;
}
+ INIT_DELAYED_WORK(&rng->dwork, sched_init_random);
old_rng = current_rng;
if (!old_rng) {
err = hwrng_init(rng);
@@ -362,6 +378,7 @@ int hwrng_register(struct hwrng *rng)
if (!old_rng) {
err = register_miscdev();
if (err) {
+ cancel_delayed_work_sync(&rng->dwork);
hwrng_cleanup(rng);
current_rng = NULL;
goto out_unlock;
@@ -395,6 +412,7 @@ void hwrng_unregister(struct hwrng *rng)
mutex_lock(&rng_mutex);
list_del(&rng->list);
+ cancel_delayed_work_sync(&rng->dwork);
if (current_rng == rng) {
hwrng_cleanup(rng);
if (list_empty(&rng_list)) {
diff --git a/include/linux/hw_random.h b/include/linux/hw_random.h
index b4b0eef..8f7370d 100644
--- a/include/linux/hw_random.h
+++ b/include/linux/hw_random.h
@@ -14,6 +14,11 @@
#include <linux/types.h>
#include <linux/list.h>
+#include <linux/workqueue.h>
+
+#define HWRNG_DELAY_READ_AT_INIT BIT(0) /* Schedule delayed work to fetch
+ * initial randomness instead of doing
+ * it at ->init()-time */
/**
* struct hwrng - Hardware Random Number Generator driver
@@ -28,6 +33,7 @@
* Must not be NULL. *OBSOLETE*
* @read: New API. drivers can fill up to max bytes of data
* into the buffer. The buffer is aligned for any type.
+ * @flags: Per-device flags.
* @priv: Private data, for use by the RNG driver.
*/
struct hwrng {
@@ -37,9 +43,11 @@ struct hwrng {
int (*data_present)(struct hwrng *rng, int wait);
int (*data_read)(struct hwrng *rng, u32 *data);
int (*read)(struct hwrng *rng, void *data, size_t max, bool wait);
+ unsigned int flags;
unsigned long priv;
/* internal. */
+ struct delayed_work dwork;
struct list_head list;
};
--
1.9.3
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