[PATCH v2] rockchip: board: Increase rng-seed size to make it sufficient for modern Linux

[PATCH v2] rockchip: board: Increase rng-seed size to make it sufficient for modern Linux

[Alex Shumsky]

Modern Linux requires 32 byte seed to initialize random pool, but u-boot
currently provides only 8 bytes. Increase rng-seed size to make Linux happy and
initialize rng pool instantly.

Boot with 8 byte rng-seed:
    # dmesg | grep crng
    [   12.089286] random: crng init done
Boot with 32 byte rng-seed:
    # dmesg | grep crng
    [    0.000000] random: crng init done

https://github.com/torvalds/linux/blob/7234e2ea0edd00bfb6bb2159e55878c19885ce68/drivers/char/random.c#L632

Signed-off-by: Alex Shumsky <alexthreed@gmail.com>
Fixes: d2048bafae40 ("rockchip: board: Add board_rng_seed() for all Rockchip devices")
---

Changes in v2:
- add env config knob rng_seed_size
- 12-character commit SHA in Fixes

 arch/arm/mach-rockchip/board.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mach-rockchip/board.c b/arch/arm/mach-rockchip/board.c
index 3fadf7e412..f9f0d7214c 100644
--- a/arch/arm/mach-rockchip/board.c
+++ b/arch/arm/mach-rockchip/board.c
@@ -472,9 +472,15 @@ __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, 32);
 	u64 *data;
 
+	if (len < 32) {
+		// rng_seed_size should be 32 bytes for Linux 5.19+, or 64 for older Linux'es
+		log_warning("Too small rng_seed_size (%lu). It is likely insufficient to init linux crng\n",
+			    len);
+	}
+
 	data = malloc(len);
 	if (!data) {
 		printf("Out of memory\n");
-- 
2.34.1

Re: [PATCH v2] rockchip: board: Increase rng-seed size to make it sufficient for modern Linux

[Dragan Simic]

Hello Alex,

Thanks for the v2.  Please see a few comments below.

On 2024-10-14 19:53, Alex Shumsky wrote:
> Modern Linux requires 32 byte seed to initialize random pool, but 
> u-boot
> currently provides only 8 bytes. Increase rng-seed size to make Linux 
> happy and
> initialize rng pool instantly.
> 
> Boot with 8 byte rng-seed:
>     # dmesg | grep crng
>     [   12.089286] random: crng init done
> Boot with 32 byte rng-seed:
>     # dmesg | grep crng
>     [    0.000000] random: crng init done
> 
> https://github.com/torvalds/linux/blob/7234e2ea0edd00bfb6bb2159e55878c19885ce68/drivers/char/random.c#L632
> 
> Signed-off-by: Alex Shumsky <alexthreed@gmail.com>
> Fixes: d2048bafae40 ("rockchip: board: Add board_rng_seed() for all
> Rockchip devices")
> ---
> 
> Changes in v2:
> - add env config knob rng_seed_size

Perhaps the emitted warning should also be mentioned here.

> - 12-character commit SHA in Fixes
> 
>  arch/arm/mach-rockchip/board.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mach-rockchip/board.c 
> b/arch/arm/mach-rockchip/board.c
> index 3fadf7e412..f9f0d7214c 100644
> --- a/arch/arm/mach-rockchip/board.c
> +++ b/arch/arm/mach-rockchip/board.c
> @@ -472,9 +472,15 @@ __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, 32);
>  	u64 *data;
> 
> +	if (len < 32) {
> +		// rng_seed_size should be 32 bytes for Linux 5.19+, or 64 for older 
> Linux'es

Shouldn't it be 8 for older kernels?

> +		log_warning("Too small rng_seed_size (%lu). It is likely
> insufficient to init linux crng\n",
> +			    len);

Perhaps this would read better:

   "Value for rng_seed_size too low (%lu) and likely insufficient
   for the Linux RNG initialization"

> +	}
> +
>  	data = malloc(len);
>  	if (!data) {
>  		printf("Out of memory\n");

Re: [PATCH v2] rockchip: board: Increase rng-seed size to make it sufficient for modern Linux

[Alex ThreeD]

On Mon, Oct 14, 2024 at 9:19 PM Dragan Simic <dsimic@manjaro.org> wrote:
> > +             // rng_seed_size should be 32 bytes for Linux 5.19+, or 64 for older
> > Linux'es
>
> Shouldn't it be 8 for older kernels?

Looking into source code I would say Linux 5.17 requires 64 bytes to init crng.
8 bytes rng_seed should help somehow, but It will not init crng instantly.
Maybe some even Linux required only 8 bytes but I doubt so.
8 bytes was too small for cryptographic PRNG yet 20 years ago.

>
> > +             log_warning("Too small rng_seed_size (%lu). It is likely
> > insufficient to init linux crng\n",
> > +                         len);
>
> Perhaps this would read better:
>
>    "Value for rng_seed_size too low (%lu) and likely insufficient
>    for the Linux RNG initialization"

Thanks, I will apply It in v3.

Re: [PATCH v2] rockchip: board: Increase rng-seed size to make it sufficient for modern Linux

[Dragan Simic]

On 2024-10-14 20:50, Alex ThreeD wrote:
> On Mon, Oct 14, 2024 at 9:19 PM Dragan Simic <dsimic@manjaro.org> 
> wrote:
>> > +             // rng_seed_size should be 32 bytes for Linux 5.19+, or 64 for older
>> > Linux'es
>> 
>> Shouldn't it be 8 for older kernels?
> 
> Looking into source code I would say Linux 5.17 requires 64 bytes to 
> init crng.
> 8 bytes rng_seed should help somehow, but It will not init crng 
> instantly.
> Maybe some even Linux required only 8 bytes but I doubt so.
> 8 bytes was too small for cryptographic PRNG yet 20 years ago.

To sum up the replies from Marek, the lower limit should be 64.

>> 
>> > +             log_warning("Too small rng_seed_size (%lu). It is likely
>> > insufficient to init linux crng\n",
>> > +                         len);
>> 
>> Perhaps this would read better:
>> 
>>    "Value for rng_seed_size too low (%lu) and likely insufficient
>>    for the Linux RNG initialization"
> 
> Thanks, I will apply It in v3.

Great, thanks!

Re: [PATCH v2] rockchip: board: Increase rng-seed size to make it sufficient for modern Linux

[Alex ThreeD]

On Mon, Oct 14, 2024 at 10:00 PM Dragan Simic <dsimic@manjaro.org> wrote:
> To sum up the replies from Marek, the lower limit should be 64.
64 by default, warning for custom values less than 32. Right?
Since 32 bytes is sufficient for kernels released in the last 2 years.

Re: [PATCH v2] rockchip: board: Increase rng-seed size to make it sufficient for modern Linux

[Dragan Simic]

On 2024-10-14 21:17, Alex ThreeD wrote:
> On Mon, Oct 14, 2024 at 10:00 PM Dragan Simic <dsimic@manjaro.org> 
> wrote:
>> To sum up the replies from Marek, the lower limit should be 64.
> 
> 64 by default, warning for custom values less than 32. Right?
> Since 32 bytes is sufficient for kernels released in the last 2 years.

I'd keep both the default and the warning threshold at 64.  I think
it's much safer that way.

Re: [PATCH v2] rockchip: board: Increase rng-seed size to make it sufficient for modern Linux

[Marek Vasut]

On 10/14/24 9:28 PM, Dragan Simic wrote:
> On 2024-10-14 21:17, Alex ThreeD wrote:
>> On Mon, Oct 14, 2024 at 10:00 PM Dragan Simic <dsimic@manjaro.org> wrote:
>>> To sum up the replies from Marek, the lower limit should be 64.
>>
>> 64 by default, warning for custom values less than 32. Right?
>> Since 32 bytes is sufficient for kernels released in the last 2 years.
> 
> I'd keep both the default and the warning threshold at 64.  I think
> it's much safer that way.

Sounds good to me, thanks !