Re: [PATCH v2] Allow hwrng to initialize crng.
On Thu, Dec 13, 2018 at 05:18:48PM +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/ Please remove these two lines. > Signed-off-by: Louis Collard > Acked-by: Jarkko Sakkinen > --- The change log seems to be missing before diffstat, after dashes. /Jarkko
Re: [PATCH v2] Allow hwrng to initialize crng.
On Thu, Dec 13, 2018 at 10:48:07AM +0100, Ard Biesheuvel wrote:
> > @@ -64,13 +65,19 @@ 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 = min_t(size_t,
> > + 2*CHACHA20_KEY_SIZE,
>
> This should be as symbolic constant that retains its meaning even if
> we move away from ChaCha20 or modify the current implementation
Also, rng_buffer_size() could be less than 2*hCHACHA20_KEY_SIZE, at
which point your goal wouldn't be realized. What I'd recommend is to
keep the line:
size_t size = min_t(size_t, 16, rng_buffer_size());
But to loop until rng_is_initialized() returns true or bytes_read is
0. If you want to be paranoid, you could also break out of the loop
it isn't initialized after, say, 8 times through the loop.
Cheers,
- Ted
Re: [PATCH v2] Allow hwrng to initialize crng.
On Thu, Dec 13, 2018 at 5:48 PM Ard Biesheuvel
wrote:
>
> On Thu, 13 Dec 2018 at 10:18, 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
> > Acked-by: Jarkko Sakkinen
> > ---
> > drivers/char/hw_random/core.c | 11 +--
> > 1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> > index 95be7228f327..7736e1a96321 100644
> > --- a/drivers/char/hw_random/core.c
> > +++ b/drivers/char/hw_random/core.c
> > @@ -24,6 +24,7 @@
> > #include
> > #include
> > #include
> > +#include
> >
> > #define RNG_MODULE_NAME"hw_random"
> >
> > @@ -64,13 +65,19 @@ 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 = min_t(size_t,
> > + 2*CHACHA20_KEY_SIZE,
>
> This should be as symbolic constant that retains its meaning even if
> we move away from ChaCha20 or modify the current implementation
>
> > + rng_buffer_size());
> >
> > mutex_lock(_mutex);
> > bytes_read = rng_get_data(rng, rng_buffer, size, 1);
> > mutex_unlock(_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)
> > --
> > 2.13.5
> >
Right, this should be [equal to] CRNG_INIT_CNT_THRESH from random.c -
I wasn't sure where/how to pull this out to though..
Re: [PATCH v2] Allow hwrng to initialize crng.
On Thu, 13 Dec 2018 at 10:18, 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
> Acked-by: Jarkko Sakkinen
> ---
> drivers/char/hw_random/core.c | 11 +--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> index 95be7228f327..7736e1a96321 100644
> --- a/drivers/char/hw_random/core.c
> +++ b/drivers/char/hw_random/core.c
> @@ -24,6 +24,7 @@
> #include
> #include
> #include
> +#include
>
> #define RNG_MODULE_NAME"hw_random"
>
> @@ -64,13 +65,19 @@ 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 = min_t(size_t,
> + 2*CHACHA20_KEY_SIZE,
This should be as symbolic constant that retains its meaning even if
we move away from ChaCha20 or modify the current implementation
> + rng_buffer_size());
>
> mutex_lock(_mutex);
> bytes_read = rng_get_data(rng, rng_buffer, size, 1);
> mutex_unlock(_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)
> --
> 2.13.5
>
