linux-kernel - Re: [RFC] Randomness on confidential computing platforms

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Message-ID: <B5BF8A36-DB2C-4CEA-8011-1708F84827D9@zytor.com>
Date: Mon, 29 Jan 2024 09:07:13 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>
CC: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "Theodore Ts'o" <tytso@....edu>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Kalra, Ashish" <ashish.kalra@....com>,
        Sean Christopherson <seanjc@...gle.com>, linux-coco@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC] Randomness on confidential computing platforms

On January 29, 2024 8:41:49 AM PST, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> wrote:
>On Mon, Jan 29, 2024 at 08:30:11AM -0800, Dave Hansen wrote:
>> On 1/26/24 05:42, Kirill A. Shutemov wrote:
>> > 3. Panic after enough re-tries of RDRAND/RDSEED instructions fail.
>> >    Another DoS variant against the Guest.
>> 
>> I think Sean was going down the same path, but I really dislike the idea
>> of having TDX-specific (or CoCo-specific) policy here.
>> 
>> How about we WARN_ON() RDRAND/RDSEED going bonkers?  The paranoid folks
>> can turn on panic_on_warn, if they haven't already.
>
>Sure, we can do it for kernel, but we have no control on what userspace
>does.
>
>Sensible userspace on RDRAND/RDSEED failure should fallback to kernel
>asking for random bytes, but who knows if it happens in practice
>everywhere.
>
>Do we care?
>

You can't fix what you can't touch.