[PATCH v5] rockchip: board: Increase rng-seed size to make it sufficient for modern Linux

[Alex Shumsky]

On Wed, Oct 16, 2024 at 4:22 AM Dragan Simic <dsimic at manjaro.org> wrote:
>
> Hello Alex,
>
> Thanks for the v5.  Please see a few comments below.
>
> On 2024-10-15 23:28, Alex Shumsky wrote:
> > Increase rng-seed size to make Linux happy and initialize rng pool
> > instantly.
> > Linux 5.19+ requires 32 bytes of entropy to initialize random pool, but
> > u-boot
> > currently provides only 8 bytes.
> > Linux 5.18 and probably some versions before it used to require 64
> > bytes.
> > Bump min value to 64 bytes to be on a safe side.
> >
> > Boot with 8 byte rng-seed (Linux 6.11):
> >     # dmesg | grep crng
> >     [   12.089286] random: crng init done
> > Boot with 32 byte rng-seed (Linux 6.11):
> >     # dmesg | grep crng
> >     [    0.000000] random: crng init done
> >
> > Linux source references:
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/char/random.c?h=v5.19#n551
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/char/random.c?h=v5.18#n236
> >
> > Signed-off-by: Alex Shumsky <alexthreed at gmail.com>
> > Fixes: d2048bafae40 ("rockchip: board: Add board_rng_seed() for all
> > Rockchip devices")
> > Reviewed-by: Dragan Simic <dsimic at manjaro.org>
> > Reviewed-by: Marek Vasut <marex at denx.de>
> > ---
> >
> > Changes in v5:
> > - add docs
> >
> > Changes in v4:
> > - fix typos and code style
> >
> > Changes in v3:
> > - reword warning
> > - increase default rng_seed_size to support older linux as well
> > - reword commit message
> >
> > Changes in v2:
> > - add env config knob rng_seed_size
> > - add warning for small rng_seed_size
> > - 12-character commit SHA in Fixes
> >
> >  arch/arm/mach-rockchip/board.c | 11 ++++++++++-
> >  common/Kconfig                 |  3 +++
> >  doc/usage/environment.rst      |  5 +++++
> >  include/fdt_support.h          |  3 ++-
> >  4 files changed, 20 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm/mach-rockchip/board.c
> > b/arch/arm/mach-rockchip/board.c
> > index 3fadf7e412..ca6404776f 100644
> > --- a/arch/arm/mach-rockchip/board.c
> > +++ b/arch/arm/mach-rockchip/board.c
> > @@ -472,9 +472,18 @@ __weak int misc_init_r(void)
> >  __weak int board_rng_seed(struct abuf *buf)
> >  {
> >       struct udevice *dev;
> > -     size_t len = 0x8;
> > +     ulong len = env_get_ulong("rng_seed_size", 10, 64);
> >       u64 *data;
> >
> > +     if (len < 64) {
> > +             /*
> > +              * rng_seed_size should be at least 32 bytes for Linux 5.19+,
> > +              * or 64 for older Linux kernel versions
> > +              */
> > +             log_warning("Value for rng_seed_size too low (%lu) and likely
> > insufficient for the Linux RNG initialization\n",
>
> Please consider changing the message to:
>
>    "Value for rng_seed_size (%lu) too low, Linux kernel RNG
>    may fail to initialize early\n"
>
> It's more compact, which is always good, and should be a bit
> more precise that way.
>
> > +                         len);
> > +     }
> > +
> >       data = malloc(len);
> >       if (!data) {
> >               printf("Out of memory\n");
> > diff --git a/common/Kconfig b/common/Kconfig
> > index 957de0c5c0..c1d06f5045 100644
> > --- a/common/Kconfig
> > +++ b/common/Kconfig
> > @@ -927,6 +927,9 @@ config BOARD_RNG_SEED
> >         new seed for use on subsequent boots, and whether or not the
> >         kernel should account any entropy from the given seed.
> >
> > +       Default seed size (64 bytes) can be overridden by a decimal
> > environment
> > +       variable rng_seed_size.
>
> Maybe reflow a bit to follow the column width above.
>
> > +
> >  endmenu
> >
> >  menu "Update support"
> > diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst
> > index cc33d3ec0f..253b25a002 100644
> > --- a/doc/usage/environment.rst
> > +++ b/doc/usage/environment.rst
> > @@ -323,6 +323,11 @@ netretry
> >      Useful on scripts which control the retry operation
> >      themselves.
> >
> > +rng_seed_size
> > +    Size of random value added to device tree-node /chosen/rng-seed.
> > +    This variable is given as a hexadecimal number.
>
> We've come to a conclusion it's a decimal number, right? :)
> So, please s/hexadecimal/decimal/
>
> > +    If unset, 64 bytes is used as the default.
> > +
> >  silent_linux
> >      If set then Linux will be told to boot silently, by
> >      adding 'console=' to its command line. If "yes" it will be
> > diff --git a/include/fdt_support.h b/include/fdt_support.h
> > index 741e2360c2..02561eab15 100644
> > --- a/include/fdt_support.h
> > +++ b/include/fdt_support.h
> > @@ -202,7 +202,8 @@ int ft_board_setup(void *blob, struct bd_info *bd);
> >   *
> >   * This function is called if CONFIG_BOARD_RNG_SEED is set, and must
> >   * be provided by the board. It should return, via @buf, some suitable
> > - * seed value to pass to the kernel.
> > + * seed value to pass to the kernel. Seed size could be set in a
> > decimal
> > + * environment variable rng_seed_size and defaulted to 64 bytes.
>
> s/defaulted/it defaults/
>

Thanks, fixed. I'm not good at wording.