linux-kernel - Re: [PATCH v2 1/1] x86/rdrand: disable RDSEED on AMD Cyan Skillfish

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Message-ID: <20260115102841.GBaWjBWbLlq-QBzA_1@fat_crate.local>
Date: Thu, 15 Jan 2026 11:28:41 +0100
From: Borislav Petkov <bp@...en8.de>
To: Travis B <tbangs89@...il.com>
Cc: me@...aill.net, dave.hansen@...ux.intel.com,
	linux-kernel@...r.kernel.org, mario.limonciello@....com,
	mingo@...hat.com, tglx@...utronix.de, x86@...nel.org
Subject: Re: [PATCH v2 1/1] x86/rdrand: disable RDSEED on AMD Cyan Skillfish

On Wed, Jan 14, 2026 at 04:41:29PM -0500, Travis B wrote:
> >It is still important, though, to make sure the user sees this and does not
> use RDSEED for generating random data used in sensitive communication.
> 
> With RDSEED cpuid bit disabled by the code, a user should
> use that to determine whether they should use the instruction
> or not.

You said it correctly: "should". But it doesn't stop her/him from still using
the instruction regardless of CPUID flag.

> It becomes the same as using any other CPU which
> already does not support RDSEED, which do not get
> a forced emergency system message for it.
> 
> pr_emerg is intended for fatal errors where the system cannot
> operate anymore. That is way above the level of RDSEED
> being disabled. There are no other places in kernel where disabling
> support for an instruction generates an emerg level message.

Ok.

You wanna send a patch and explain the justification for the change properly
in the commit message?

Thx.

-- 
Regards/Gruss,
    Boris.

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