Received-SPF: pass (google.com: domain of linux-kernel+bounces-106774-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
From: Michael Kelley <mhklinux@outlook.com>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
CC: "haiyangz@microsoft.com" <haiyangz@microsoft.com>, "wei.liu@kernel.org"
	<wei.liu@kernel.org>, "decui@microsoft.com" <decui@microsoft.com>,
	"catalin.marinas@arm.com" <catalin.marinas@arm.com>, "will@kernel.org"
	<will@kernel.org>, "tglx@linutronix.de" <tglx@linutronix.de>,
	"mingo@redhat.com" <mingo@redhat.com>, "bp@alien8.de" <bp@alien8.de>,
	"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>, "hpa@zytor.com"
	<hpa@zytor.com>, "arnd@arndb.de" <arnd@arndb.de>, "tytso@mit.edu"
	<tytso@mit.edu>, "x86@kernel.org" <x86@kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Subject: RE: [PATCH v3 1/1] x86/hyperv: Use Hyper-V entropy to seed guest
 random number generator
Thread-Topic: [PATCH v3 1/1] x86/hyperv: Use Hyper-V entropy to seed guest
 random number generator
Thread-Index: AQHaeUyZvwlmluIhS0+V4P/P+ldkWLE9/NGAgAAdLDA=
Date: Mon, 18 Mar 2024 22:49:58 +0000
Message-ID:
 <SN6PR02MB4157453833547D915BF3F326D42D2@SN6PR02MB4157.namprd02.prod.outlook.com>
References: <20240318155408.216851-1-mhklinux@outlook.com>
 <ZfisGSPX9et2hGzx@zx2c4.com>
In-Reply-To: <ZfisGSPX9et2hGzx@zx2c4.com>
Accept-Language: en-US
Content-Language: en-US
x-ms-exchange-antispam-messagedata-chunkcount: 1
x-ms-exchange-antispam-messagedata-0:
 =?us-ascii?Q?O/GQgU5oslylRLhqsvsuV+l54u523uEE5ufPK/L0odYZTEUUPQ0Ej9sAXL3A?=
 =?us-ascii?Q?FSLylDoOHjwO7KKbS5evZRWHF52iOpBljLNrnX8HCI3iTPye9qek4T2ioIpr?=
 =?us-ascii?Q?Q95+J0TWf6UKPe4yaLs4vcuX0+URw6EFOELeuBsOPfjFxMX/nddTZZPTavI5?=
 =?us-ascii?Q?UcuZwqnUmYYRt5uDLDwwB1IIMmX1gLPOXWCoYOToVUjHqO2l6cqy9IFKu4ad?=
 =?us-ascii?Q?wNf/GNk/wltEk/cpEycgRSTYygHCW+rlTWhETpadQrheFTJRsvAEKx+Iw74+?=
 =?us-ascii?Q?eHL0p9pM1yoHpbIWWpgUfEQRQLLifNUkshKWNw+AqSvLhd0B1+chXXM1q0Gw?=
 =?us-ascii?Q?D/aboRb3XvT7q6nkt5cjLNFZwwwcVubjITQoffMBplr9/5wR2tFQtbnscZwc?=
 =?us-ascii?Q?yv/eyZAxIfwEidRsRBvlDL04VcvIF9eth5QF9u45cjkXIXkTLS5K8z0CtYYL?=
 =?us-ascii?Q?N2TP2jOO6qNEcyvEDQUpQrkkhFS+BIBdaVlzbz7DG5Ihwv5SR+3X3jCGRSDs?=
 =?us-ascii?Q?wfhCArEkq8AvY3Bg9ggpo6lVgAWwkDxKkjmyCeRwvFXj2riguH3zomOiJy6X?=
 =?us-ascii?Q?BJRWlaCPDDrw95vzNmYH3ZQlAH0IFaVg8q+XxOcG44/xBpixbGTyH17ZJbUg?=
 =?us-ascii?Q?8195QOWdTUopYp699R5a7KTYYBDnZCsNaS9Z6Bihj2OIqboN5b1x3DmeQQRr?=
 =?us-ascii?Q?0HSCw/mGVQyxhEuqByZQJOr1+6bWa2IYTj2mKyLn9gHi0nB4kyvrcBWsSzw8?=
 =?us-ascii?Q?UjXb1rPBMNVbJn3ag9qDAnPBo6haNe0Udak+x3Y49Qg2CbYkEMIEm7QUoUB6?=
 =?us-ascii?Q?7T83icVrHP4APMyXf7YPxtKkgNJJcq3K4/nkxXMKT+vsvAhi7V3rqiN2mAvY?=
 =?us-ascii?Q?Xo8/iRLf0VMAEyatjPJWpym6fdbegiSNeDyRKehpJR3pJuQzW0ewqgxHfrwA?=
 =?us-ascii?Q?vumlI9MHwkLtcxl4zxlURloW8C+6ufEt2XQ3E3OxnUCvTr/t0h/Rbg5IOdfF?=
 =?us-ascii?Q?KiJdLsXpdp0+qYJrJ6Q0EweW8MAQi4Z11E4CwmmsW/VL97Fg66lOKOqS06h7?=
 =?us-ascii?Q?EaHqWZNtE7fcq1Pihu4+ZcZOrX1+GJBhFwg17atBb0rVJa+dZH+uxT97fiRl?=
 =?us-ascii?Q?MqP3tLb99/EK8sit8r4nA5khGDkxcQ89zQtAHEX2pyc9z+0wMKWq+R0Kvkyz?=
 =?us-ascii?Q?aCJ68oqrr9KQLBpClxkcmmv2r75Ifum2tqb/fw=3D=3D?=
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk
X-Mailing-List: linux-kernel@vger.kernel.org
List-Id: <linux-kernel.vger.kernel.org>
List-Subscribe: <mailto:linux-kernel+subscribe@vger.kernel.org>
List-Unsubscribe: <mailto:linux-kernel+unsubscribe@vger.kernel.org>
MIME-Version: 1.0
X-OriginatorOrg: outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-AuthSource: SN6PR02MB4157.namprd02.prod.outlook.com
X-MS-Exchange-CrossTenant-RMS-PersistedConsumerOrg: 00000000-0000-0000-0000-000000000000
X-MS-Exchange-CrossTenant-Network-Message-Id: f31aa55f-b56b-4054-1929-08dc479dbcdb
X-MS-Exchange-CrossTenant-rms-persistedconsumerorg: 00000000-0000-0000-0000-000000000000
X-MS-Exchange-CrossTenant-originalarrivaltime: 18 Mar 2024 22:49:58.3559
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 84df9e7f-e9f6-40af-b435-aaaaaaaaaaaa
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR02MB6844

From: Jason A. Donenfeld <Jason@zx2c4.com> Sent: Monday, March 18, 2024 2:0=
3 PM
>=20
> On Mon, Mar 18, 2024 at 08:54:08AM -0700, mhkelley58@gmail.com wrote:
> > From: Michael Kelley <mhklinux@outlook.com>
> >
> > A Hyper-V host provides its guest VMs with entropy in a custom ACPI
> > table named "OEM0".  The entropy bits are updated each time Hyper-V
> > boots the VM, and are suitable for seeding the Linux guest random
> > number generator (rng). See a brief description of OEM0 in [1].
> >
> > Generation 2 VMs on Hyper-V use UEFI to boot. Existing EFI code in
> > Linux seeds the rng with entropy bits from the EFI_RNG_PROTOCOL.
> > Via this path, the rng is seeded very early during boot with good
> > entropy. The ACPI OEM0 table provided in such VMs is an additional
> > source of entropy.
> >
> > Generation 1 VMs on Hyper-V boot from BIOS. For these VMs, Linux
> > doesn't currently get any entropy from the Hyper-V host. While this
> > is not fundamentally broken because Linux can generate its own entropy,
> > using the Hyper-V host provided entropy would get the rng off to a
> > better start and would do so earlier in the boot process.
> >
> > Improve the rng seeding for Generation 1 VMs by having Hyper-V specific
> > code in Linux take advantage of the OEM0 table to seed the rng. For
> > Generation 2 VMs, use the OEM0 table to provide additional entropy
> > beyond the EFI_RNG_PROTOCOL. Because the OEM0 table is custom to
> > Hyper-V, parse it directly in the Hyper-V code in the Linux kernel
> > and use add_bootloader_randomness() to add it to the rng. Once the
> > entropy bits are read from OEM0, zero them out in the table so
> > they don't appear in /sys/firmware/acpi/tables/OEM0 in the running
> > VM. The zero'ing is done out of an abundance of caution to avoid
> > potential security risks to the rng. Also set the OEM0 data length
> > to zero so a kexec or other subsequent use of the table won't try
> > to use the zero'ed bits.
> >
> > [1] https://download.microsoft.com/download/1/c/9/1c9813b8-089c-4fef-b2=
ad-ad80e79403ba/Whitepaper%20-%20The%20Windows%2010%20random%20number%20gen=
eration%20infrastructure.pdf=20
>=20
> Looks good to me. Assuming you've tested this and it works,

Yes, tested on both x86 and arm64.  Thanks.

Michael

>=20
>  Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com>
>=20
> Thanks for the v3.
>=20
> Jason