[PATCH v6] rockchip: board: Increase rng-seed size to make it sufficient for modern Linux

[Dragan Simic]

Hello Alex,

On 2024-10-16 12:02, 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 v6:
> - fix wording in docs and debug message

Thanks for the v6, it's looking good to me.  I think I have
no more suggestions, :) and I'm sorry for the little bit of
back and forth.

> 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..75d6693e28 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 (%lu) too low, Linux kernel
> RNG may fail to initialize early\n",
> +			    len);
> +	}
> +
>  	data = malloc(len);
>  	if (!data) {
>  		printf("Out of memory\n");
> diff --git a/common/Kconfig b/common/Kconfig
> index 957de0c5c0..8098f90683 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.
> +
>  endmenu
> 
>  menu "Update support"
> diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst
> index cc33d3ec0f..7bd9ffce8d 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 decimal number.
> +    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..9447a64e06 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 it defaults to 64 bytes.
>   *
>   * @param buf         A struct abuf for returning the seed and its 
> size.
>   * @return            0 if ok, negative on error.