linux-kernel - Re: [PATCH 1/2] x86/random: Retry on RDSEED failure

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Date: Wed, 14 Feb 2024 10:34:48 +0200
From: Nikolay Borisov <nik.borisov@...e.com>
To: Theodore Ts'o <tytso@....edu>, Dan Williams <dan.j.williams@...el.com>
Cc: "Reshetova, Elena" <elena.reshetova@...el.com>,
 "Jason A. Donenfeld" <Jason@...c4.com>,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>,
 Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>,
 "Nakajima, Jun" <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-coco@...ts.linux.dev>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] x86/random: Retry on RDSEED failure

On 14.02.24 г. 6:32 ч., Theodore Ts'o wrote:
> On Tue, Feb 13, 2024 at 04:53:06PM -0800, Dan Williams wrote:
>>
>> Indeed it is. Typically when you have x86, riscv, arm, and s390 folks
>> all show up at a Linux Plumbers session [1] to talk about their approach
>> to handling a new platform paradigm, that is a decent indication that
>> the technology is more real than not. Point taken that it is not here
>> today, but it is also not multiple hardware generations away as the
>> Plumbers participation indicated.
> 
> My big concerns with TDISP which make me believe it may not be a
> silver bullet is that (a) it's hyper-complex (although to be fair
> Confidential Compute isn't exactly simple, and (b) it's one thing to
> digitally sign software so you know that it comes from a trusted
> source; but it's a **lot** harder to prove that hardware hasn't been
> tampered with --- a digital siganture can't tell you much about
> whether or not the hardware is in an as-built state coming from the
> factory --- this requires things like wrapping the device with
> resistive wire in multiple directions with a whetstone bridge to
> detect if the wire has gotten cut or shorted, then dunking the whole
> thing in epoxy, so that any attempt to tamper with the hardware will
> result it self-destructing (via a thermite charge or equivalent :-)

This really reminds me of the engineering that goes into the omnipresent 
POS terminals ate every store, since they store certificates from the 
card (Visa/Master) operators. So I wonder if at somepoint we'll have a 
pos-like device (by merit of its engineering) in every server....

> 
> Remember, the whole conceit of Confidential Compute is that you don't
> trust the cloud provider --- but if that entity controls the PCI cards
> installed in their servers, and and that entity has the ability to
> *modify* the PCI cards in the server, all of the digital signatures
> and fancy-schmancy TDISP complexity isn't necessarily going to save
> you.

Can't the same argument go for the CPU, though it's a lot more 
"integrated" into the silicong substrate, yet we somehow believe CoCo 
ascertains that a vm is running on trusted hardware? But ultimately the 
CPU is still a part that comes from the untrusted CSP.

<snip>