Start the hwrng kthread even if the hwrng source has a quality setting
of zero. Then, every CRNG_RESEED_INTERVAL, one batch of data from this
zero-quality hwrng source will be mixed into the CRNG pool.
However, to avoid that an untrusted device assists in initializing the
CRNG, go to sleep in add_hwgenerator_randomness() in case the entropy
parameter passed to that function is zero.
This patch is based on the assumption that data from a hwrng source
will not actively harm the CRNG state, but that many hwrng sources
(such as TPM devices), even though they are assigend a quality level of
zero, actually provide some entropy, which is good to mix into the CRNG
pool every once in a while.
Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Cc: Jason A. Donenfeld <Jason@xxxxxxxxx>
Signed-off-by: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx>
---
drivers/char/hw_random/core.c | 36 ++++++++++-------------------------
drivers/char/random.c | 4 ++--
2 files changed, 12 insertions(+), 28 deletions(-)
diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
index 16f227b995e8..edb86c0cccda 100644
--- a/drivers/char/hw_random/core.c
+++ b/drivers/char/hw_random/core.c
@@ -52,7 +52,7 @@ MODULE_PARM_DESC(default_quality,
static void drop_current_rng(void);
static int hwrng_init(struct hwrng *rng);
-static void hwrng_manage_rngd(struct hwrng *rng);
+static int hwrng_fillfn(void *unused);
static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
int wait);
@@ -96,6 +96,15 @@ static int set_current_rng(struct hwrng *rng)
drop_current_rng();
current_rng = rng;
+ /* if necessary, start hwrng thread */
+ if (!hwrng_fill) {
+ hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
+ if (IS_ERR(hwrng_fill)) {
+ pr_err("hwrng_fill thread creation failed\n");
+ hwrng_fill = NULL;
+ }
+ }
+
return 0;
}
@@ -167,8 +176,6 @@ static int hwrng_init(struct hwrng *rng)
rng->quality = 1024;
current_quality = rng->quality; /* obsolete */
- hwrng_manage_rngd(rng);
-
return 0;
}
@@ -454,10 +461,6 @@ static ssize_t rng_quality_store(struct device *dev,
/* the best available RNG may have changed */
ret = enable_best_rng();
- /* start/stop rngd if necessary */
- if (current_rng)
- hwrng_manage_rngd(current_rng);
-
out:
mutex_unlock(&rng_mutex);
return ret ? ret : len;
@@ -509,9 +512,6 @@ static int hwrng_fillfn(void *unused)
mutex_unlock(&reading_mutex);
put_rng(rng);
- if (!quality)
- break;
-
if (rc <= 0) {
pr_warn("hwrng: no data available\n");
msleep_interruptible(10000);
@@ -533,22 +533,6 @@ static int hwrng_fillfn(void *unused)
return 0;
}
-static void hwrng_manage_rngd(struct hwrng *rng)
-{
- if (WARN_ON(!mutex_is_locked(&rng_mutex)))
- return;
-
- if (rng->quality == 0 && hwrng_fill)
- kthread_stop(hwrng_fill);
- if (rng->quality > 0 && !hwrng_fill) {
- hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
- if (IS_ERR(hwrng_fill)) {
- pr_err("hwrng_fill thread creation failed\n");
- hwrng_fill = NULL;
- }
- }
-}
-
int hwrng_register(struct hwrng *rng)
{
int err = -EINVAL;
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 79d7d4e4e582..b360ed4ece03 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -867,9 +867,9 @@ void add_hwgenerator_randomness(const void *buf, size_t len, size_t entropy)
/*
* Throttle writing to once every CRNG_RESEED_INTERVAL, unless
- * we're not yet initialized.
+ * we're not yet initialized or this source isn't trusted.
*/
- if (!kthread_should_stop() && crng_ready())
+ if (!kthread_should_stop() && (crng_ready() || !entropy))
schedule_timeout_interruptible(CRNG_RESEED_INTERVAL);
}
EXPORT_SYMBOL_GPL(add_hwgenerator_randomness);
--
2.37.3
