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

Borislav Petkov
2022-07-05T19:36:32Z

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.