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. This patch is based on the assumption that data from a hwrng source will not actively harm the CRNG state. Instead, many hwrng sources (such as TPM devices), even though they are assigend a quality level of zero, actually provide some entropy, which is good enough 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> --- Thanks to Jason for splitting my v1 into two parts, as per Herbert's request. In comparison to v2, I've updated (and shortened) the commit message. 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;