From b006c439d58db625318bf2207feabf847510a8a6 Mon Sep 17 00:00:00 2001 From: Dominik Brodowski Date: Thu, 22 Sep 2022 15:59:31 +0200 Subject: [PATCH] hwrng: core - start hwrng kthread also for untrusted sources 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 Cc: Jason A. Donenfeld Signed-off-by: Dominik Brodowski Signed-off-by: Herbert Xu --- drivers/char/hw_random/core.c | 36 ++++++++++-------------------------- 1 file changed, 10 insertions(+), 26 deletions(-) diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index d7045df..cc002b0 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 @@ skip_init: 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; @@ -513,9 +516,6 @@ static int hwrng_fillfn(void *unused) put_rng(rng); - if (!quality) - break; - if (rc <= 0) continue; @@ -534,22 +534,6 @@ 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; -- 2.7.4