Re: [RESEND PATCH] Allow hwrng to initialize crng.
From: Herbert Xu
Date: Thu Dec 13 2018 - 03:51:31 EST
On Thu, Dec 13, 2018 at 04:40:17PM +0800, Louis Collard wrote:
> Some systems, for example embedded systems, do not generate
> enough entropy on boot through interrupts, and boot may be blocked for
> several minutes waiting for a call to getrandom to complete.
> Currently, random data is read from a hwrng when it is registered,
> and is loaded into primary_crng. This data is treated in the same
> way as data that is device-specific but otherwise unchanging, and
> so primary_crng cannot become initialized with the data from the
> This change causes the data initially read from the hwrng to be
> treated the same as subsequent data that is read from the hwrng if
> it's quality score is non-zero.
> The implications of this are:
> The data read from hwrng can cause primary_crng to become
> initialized, therefore avoiding problems of getrandom blocking
> on boot.
> Calls to getrandom (with GRND_RANDOM) may be using entropy
> exclusively (or in practise, almost exclusively) from the hwrng.
> Regarding the latter point; this behavior is the same as if a
> user specified a quality score of 1 (bit of entropy per 1024 bits)
> so hopefully this is not too scary a change to make.
> This change is the result of the discussion here:
> Signed-off-by: Louis Collard <louiscollard@xxxxxxxxxxxx>
> Acked-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
> drivers/char/hw_random/core.c | 9 +++++++--
> 1 file changed, 7 insertions(+), 2 deletions(-)
> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> index 95be7228f327..99c3e4127949 100644
> --- a/drivers/char/hw_random/core.c
> +++ b/drivers/char/hw_random/core.c
> @@ -24,6 +24,7 @@
> #include <linux/sched.h>
> #include <linux/slab.h>
> #include <linux/uaccess.h>
> +#include <crypto/chacha20.h>
> #define RNG_MODULE_NAME "hw_random"
> @@ -64,13 +65,17 @@ static size_t rng_buffer_size(void)
> static void add_early_randomness(struct hwrng *rng)
> int bytes_read;
> - size_t size = min_t(size_t, 16, rng_buffer_size());
> + /* Read enough to initialize crng. */
> + size_t size = 2*CHACHA20_KEY_SIZE;
> bytes_read = rng_get_data(rng, rng_buffer, size, 1);
> if (bytes_read > 0)
> - add_device_randomness(rng_buffer, bytes_read);
> + /* Allow crng to become initialized, but do not add
> + * entropy to the pool.
> + */
> + add_hwgenerator_randomness(rng_buffer, bytes_read, 0);
> static inline void cleanup_rng(struct kref *kref)
Adding Ted Ts'o to the cc list.
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt