Re: [XEN PATCH v1] libxl/arm: provide guests with random seed

[Julien Grall <julien@xxxxxxx>]

Hi,

On 24/05/2021 09:00, Sergiy Kibrik wrote:
> Pass random seed via FDT, so that guests' CRNGs are better seeded early at boot.
> Depending on its configuration Linux can use the seed as device randomness
> or to just quickly initialize CRNG.
> In either case this will provide extra randomness to further harden CRNG.
>
> Signed-off-by: Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>
> ---
>   tools/libxl/libxl_arm.c | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/tools/libxl/libxl_arm.c b/tools/libxl/libxl_arm.c
> index 34f8a29056..05c58a428c 100644
> --- a/tools/libxl/libxl_arm.c
> +++ b/tools/libxl/libxl_arm.c
> @@ -342,6 +342,12 @@ static int make_chosen_node(libxl__gc *gc, void *fdt, bool 
> ramdisk,
>           if (res) return res;
>       }
>   
> +    uint8_t seed[128];
I couldn't find any documentation for the property (although, I have 
found code in Linux). Can you explain where the 128 come from?
Also, local variables should be defined at the beginning of the function.

> +    res = libxl__random_bytes(gc, seed, sizeof(seed)); > +    if (res) return 
> res;
> +    res = fdt_property(fdt, "rng-seed", seed, sizeof(seed));
> +    if (res) return res;
> +
>       res = fdt_end_node(fdt);
>       if (res) return res;
Cheers,

--
Julien Grall