Re: [PATCH] random: remove CONFIG_ARCH_RANDOM and "nordrand"

From: Borislav Petkov <bp@alien8.de>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: linux-arm-kernel@lists.infradead.org,
	linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Heiko Carstens <hca@linux.ibm.com>,
	Alexander Gordeev <agordeev@linux.ibm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH] random: remove CONFIG_ARCH_RANDOM and "nordrand"
Date: Tue, 5 Jul 2022 21:36:20 +0200	[thread overview]
Message-ID: <YsSStCQQf008hF2F@zn.tnic> (raw)
In-Reply-To: <20220705190121.293703-1-Jason@zx2c4.com>

On Tue, Jul 05, 2022 at 09:01:21PM +0200, Jason A. Donenfeld wrote:
> @@ -26,7 +18,6 @@ __setup("nordrand", x86_rdrand_setup);
>   */
>  #define SANITY_CHECK_LOOPS 8
>  
> -#ifdef CONFIG_ARCH_RANDOM
>  void x86_init_rdrand(struct cpuinfo_x86 *c)
>  {
>  	unsigned int changed = 0;
> @@ -59,8 +50,6 @@ void x86_init_rdrand(struct cpuinfo_x86 *c)
>  	}
>  
>  	if (WARN_ON_ONCE(!changed))
> -		pr_emerg(
> -"RDRAND gives funky smelling output, might consider not using it by booting with \"nordrand\"");
> +		pr_emerg("RDRAND gives funky smelling output; update microcode or firmware.");

It is highly unlikely to get a BIOS or microcode update for that matter,
for old systems:

7879fc4bdc75 ("x86/rdrand: Sanity-check RDRAND output")

so I guess here you're better off saying that the kernel simply disables
rdrand support and do

	clear_cpu_cap(c, X86_FEATURE_RDRAND);

here too.

If I read the commit message above correctly, it sounds like RDRAND
output is not that important anyway...

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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