linux-kernel - Re: [PATCH] arm64: head: rely on CONFIG_RANDOM_TRUST

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Date:   Wed, 17 Aug 2022 14:51:43 +0100
From:   Will Deacon <will@...nel.org>
To:     Andrea Righi <andrea.righi@...onical.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: head: rely on CONFIG_RANDOM_TRUST_CPU

On Wed, Aug 17, 2022 at 11:46:18AM +0200, Andrea Righi wrote:
> The CONFIG_ARCH_RANDOM .config option has been removed by
> commit 9592eef7c16e ("random: remove CONFIG_ARCH_RANDOM").
> 
> Depend on CONFIG_RANDOM_TRUST_CPU to determine whether we can rely on
> __arm64_rndr() to initialize the seed for kaslr.
> 
> Fixes: 9592eef7c16e ("random: remove CONFIG_ARCH_RANDOM")
> Signed-off-by: Andrea Righi <andrea.righi@...onical.com>
> ---
>  arch/arm64/kernel/pi/kaslr_early.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/pi/kaslr_early.c b/arch/arm64/kernel/pi/kaslr_early.c
> index 6c3855e69395..a1e6f90cb6e2 100644
> --- a/arch/arm64/kernel/pi/kaslr_early.c
> +++ b/arch/arm64/kernel/pi/kaslr_early.c
> @@ -94,7 +94,7 @@ asmlinkage u64 kaslr_early_init(void *fdt)
>  
>  	seed = get_kaslr_seed(fdt);
>  	if (!seed) {
> -#ifdef CONFIG_ARCH_RANDOM
> +#ifdef CONFIG_RANDOM_TRUST_CPU
>  		 if (!__early_cpu_has_rndr() ||
>  		     !__arm64_rndr((unsigned long *)&seed))
>  #endif

There was another patch sent for this which just removed the guard
altogether:

https://lore.kernel.org/r/20220721100433.18286-1-lukas.bulwahn@gmail.com

I was planning to pick that one up as a fix for -rc2 as Ard was happy
with it and it matches what Broonie was after as well.

Will