On Sun, Nov 18, 2018 at 4:15 AM Michael Niewöhner <linux@xxxxxxxxxxxxxx> wrote: > > Hi Louis, > > On Wed, 2018-09-26 at 11:24 +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 > > hwrng. > > > > 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: > > https://patchwork.kernel.org/patch/10453893/ > > > > 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 aaf9e5afaad4..47f358aa0c3d 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; > > > > mutex_lock(&reading_mutex); > > bytes_read = rng_get_data(rng, rng_buffer, size, 1); > > mutex_unlock(&reading_mutex); > > 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) > > I found your patch by chance, searching for a solution for crng init delay on my > headless machine. Unfortunately it hardly makes any difference for me. With the > patch the system hangs for about 80s instead of 120s until the "crng init done" > message.In contrast, doing a `cat /dev/hwrng >/dev/random` or running rngd > initializes the crng instantly. > > Isn't that delay the problem this patch tries to fix? Any idea what is wrong > here? > > Thanks! > > Best regards > Michael > > Yes that is the problem this is trying to address. My guess would be rng_get_data() is not returning as much data as requested, so the delay is reduced but not eliminated. Looking at implementation of rng_get_data() it appears this could be caused by device support for read() vs data_read(). I don't have a good feel for whether looping to retrieve more data here would be acceptable, it is certainly a bigger change than currently proposed. Thanks, Louis
