linux-kernel - Re: [PATCH] m68k: virt: pass RNG seed via bootinfo block

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Date:   Sat, 25 Jun 2022 18:08:37 +0200
From:   Laurent Vivier <laurent@...ier.eu>
To:     "Jason A. Donenfeld" <Jason@...c4.com>, geert@...ux-m68k.org,
        linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] m68k: virt: pass RNG seed via bootinfo block

Le 25/06/2022 à 17:38, Jason A. Donenfeld a écrit :
> Other virt VMs can pass RNG seeds via the "rng-seed" device tree
> property or via UEFI, but m68k doesn't have either. Instead it has its
> own bootinfo protocol. So this commit adds support for receiving a RNG
> seed from it, which will be used at the earliest possible time in boot,
> just like device tree.
> 
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
>   arch/m68k/include/uapi/asm/bootinfo-virt.h | 1 +
>   arch/m68k/virt/config.c                    | 4 ++++
>   2 files changed, 5 insertions(+)
> 
> diff --git a/arch/m68k/include/uapi/asm/bootinfo-virt.h b/arch/m68k/include/uapi/asm/bootinfo-virt.h
> index e4db7e2213ab..7c3044acdf4a 100644
> --- a/arch/m68k/include/uapi/asm/bootinfo-virt.h
> +++ b/arch/m68k/include/uapi/asm/bootinfo-virt.h
> @@ -12,6 +12,7 @@
>   #define BI_VIRT_GF_TTY_BASE	0x8003
>   #define BI_VIRT_VIRTIO_BASE	0x8004
>   #define BI_VIRT_CTRL_BASE	0x8005
> +#define BI_VIRT_RNG_SEED	0x8006
>   
>   #define VIRT_BOOTI_VERSION	MK_BI_VERSION(2, 0)
>   
> diff --git a/arch/m68k/virt/config.c b/arch/m68k/virt/config.c
> index 632ba200ad42..ad71af8273ec 100644
> --- a/arch/m68k/virt/config.c
> +++ b/arch/m68k/virt/config.c
> @@ -2,6 +2,7 @@
>   
>   #include <linux/reboot.h>
>   #include <linux/serial_core.h>
> +#include <linux/random.h>
>   #include <clocksource/timer-goldfish.h>
>   
>   #include <asm/bootinfo.h>
> @@ -92,6 +93,9 @@ int __init virt_parse_bootinfo(const struct bi_record *record)
>   		data += 4;
>   		virt_bi_data.virtio.irq = be32_to_cpup(data);
>   		break;
> +	case BI_VIRT_RNG_SEED:
> +		add_bootloader_randomness(data + 4, be32_to_cpup(data));

In fact, why don't you use the record->size to get the size of the buffer?

It seems useless to encode twice the length of the buffer, the second time on a 32bit while the 
length cannot exceed a 16bit value.

Thanks,
Laurent