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From: "Jason A. Donenfeld" <Jason@zx2c4.com>
Date: Thu, 22 Feb 2024 00:09:32 +0100
Message-ID: <CAHmME9rCQgY_DMmpOEJWO8qytNw3ErJNy9L-E7WzEKYHVyqCHA@mail.gmail.com>
Subject: Re: [PATCH v3] x86/coco: Require seeding RNG with RDRAND on CoCo systems
To: Dave Hansen <dave.hansen@intel.com>
Cc: x86@kernel.org, linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, 
	Borislav Petkov <bp@alien8.de>, =?UTF-8?Q?Daniel_P_=2E_Berrang=C3=A9?= <berrange@redhat.com>, 
	Dave Hansen <dave.hansen@linux.intel.com>, Elena Reshetova <elena.reshetova@intel.com>, 
	"H . Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>, 
	"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, "Theodore Ts'o" <tytso@mit.edu>, 
	Thomas Gleixner <tglx@linutronix.de>
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On Wed, Feb 21, 2024 at 11:47=E2=80=AFPM Dave Hansen <dave.hansen@intel.com=
> wrote:
> OK, so we're trying to get 256 bits of seed data from RDRAND?

Yes. This fills a 32-byte buffer of longs up with output from
arch_get_random_longs().

> But no pattern I could discern.  Did you mean something different by
> "platform drivers"?

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arc=
h/um/kernel/um_arch.c#n413
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/dri=
vers/char/random.c#n655
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scr=
ipts/gcc-plugins/latent_entropy_plugin.c#n90


> If we're going to have arch/x86-specific crud, it would be great to make
> it obvious and straightforward to those of us simple folk that are
> familiar with arch/x86 code.

If you insist, I'll stick a local `enum { RANDOM_BYTES_COUNT =3D 32 }`
in that function or something. Seems unnecessary to me but if that's
what you need no problem. Would that suffice? Or a different variable
name? Or a comment on "what is 32 about?"

Jason