From: Tom Lendacky <thomas.lendacky@amd.com>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>, Borislav Petkov <bp@alien8.de>
Cc: x86@kernel.org, linux-coco@lists.linux.dev,
linux-kernel@vger.kernel.org,
"Daniel P . Berrangé" <berrange@redhat.com>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
"H . Peter Anvin" <hpa@zytor.com>,
"Ingo Molnar" <mingo@redhat.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
stable@vger.kernel.org,
"Elena Reshetova" <elena.reshetova@intel.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
"Theodore Ts'o" <tytso@mit.edu>
Subject: Re: [PATCH v6] x86/coco: Require seeding RNG with RDRAND on CoCo systems
Date: Thu, 28 Mar 2024 10:13:23 -0500 [thread overview]
Message-ID: <21acb22c-3b02-44bd-bc61-9fa4435eedf5@amd.com> (raw)
In-Reply-To: <20240326160735.73531-1-Jason@zx2c4.com>
On 3/26/24 11:07, Jason A. Donenfeld wrote:
> There are few uses of CoCo that don't rely on working cryptography and
> hence a working RNG. Unfortunately, the CoCo threat model means that the
> VM host cannot be trusted and may actively work against guests to
> extract secrets or manipulate computation. Since a malicious host can
> modify or observe nearly all inputs to guests, the only remaining source
> of entropy for CoCo guests is RDRAND.
>
> If RDRAND is broken -- due to CPU hardware fault -- the RNG as a whole
> is meant to gracefully continue on gathering entropy from other sources,
> but since there aren't other sources on CoCo, this is catastrophic.
> This is mostly a concern at boot time when initially seeding the RNG, as
> after that the consequences of a broken RDRAND are much more
> theoretical.
>
> So, try at boot to seed the RNG using 256 bits of RDRAND output. If this
> fails, panic(). This will also trigger if the system is booted without
> RDRAND, as RDRAND is essential for a safe CoCo boot.
>
> This patch is deliberately written to be "just a CoCo x86 driver
> feature" and not part of the RNG itself. Many device drivers and
> platforms have some desire to contribute something to the RNG, and
> add_device_randomness() is specifically meant for this purpose. Any
> driver can call this with seed data of any quality, or even garbage
> quality, and it can only possibly make the quality of the RNG better or
> have no effect, but can never make it worse. Rather than trying to
> build something into the core of the RNG, this patch interprets the
> particular CoCo issue as just a CoCo issue, and therefore separates this
> all out into driver (well, arch/platform) code.
>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Daniel P. Berrangé <berrange@redhat.com>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: stable@vger.kernel.org
> Reviewed-by: Elena Reshetova <elena.reshetova@intel.com>
> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Reviewed-by: Theodore Ts'o <tytso@mit.edu>
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Tested-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
> Changes v5->v6:
> - Rebase on tip/master.
> - Add string.h include.
>
> arch/x86/coco/core.c | 41 +++++++++++++++++++++++++++++++++++++
> arch/x86/include/asm/coco.h | 2 ++
> arch/x86/kernel/setup.c | 2 ++
> 3 files changed, 45 insertions(+)
>
next prev parent reply other threads:[~2024-03-28 15:13 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-21 12:32 [PATCH v3] x86/coco: Require seeding RNG with RDRAND on CoCo systems Jason A. Donenfeld
2024-02-21 14:34 ` Reshetova, Elena
2024-02-21 15:36 ` Jason A. Donenfeld
2024-02-21 15:37 ` Kirill A . Shutemov
2024-02-21 15:51 ` Theodore Ts'o
2024-02-21 16:55 ` Dave Hansen
2024-02-21 17:19 ` Jason A. Donenfeld
2024-02-21 22:47 ` Dave Hansen
2024-02-21 23:09 ` Jason A. Donenfeld
2024-02-21 23:35 ` Dave Hansen
2024-02-22 2:05 ` [PATCH v4] " Jason A. Donenfeld
2024-02-23 22:05 ` Tom Lendacky
2024-02-24 1:14 ` Jason A. Donenfeld
2024-02-24 1:18 ` [PATCH v5] " Jason A. Donenfeld
2024-03-13 23:34 ` Jason A. Donenfeld
2024-03-14 11:14 ` Borislav Petkov
2024-03-26 11:21 ` Borislav Petkov
2024-03-26 16:07 ` [PATCH v6] " Jason A. Donenfeld
2024-03-28 15:13 ` Tom Lendacky [this message]
2024-02-22 7:35 ` [PATCH v3] " Reshetova, Elena
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