From: Alexander Graf <graf@amazon.com>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>,
<linux-kernel@vger.kernel.org>, <linux-crypto@vger.kernel.org>,
<qemu-devel@nongnu.org>, <kvm@vger.kernel.org>,
<linux-s390@vger.kernel.org>, <adrian@parity.io>
Cc: <dwmw@amazon.co.uk>, <acatan@amazon.com>, <colmmacc@amazon.com>,
<sblbir@amazon.com>, <raduweis@amazon.com>, <jannh@google.com>,
<gregkh@linuxfoundation.org>, <tytso@mit.edu>
Subject: Re: [PATCH RFC v1 0/2] VM fork detection for RNG
Date: Thu, 24 Feb 2022 09:53:59 +0100 [thread overview]
Message-ID: <234d7952-0379-e3d9-5e02-5eba171024a0@amazon.com> (raw)
In-Reply-To: <20220223131231.403386-1-Jason@zx2c4.com>
Hey Jason,
On 23.02.22 14:12, Jason A. Donenfeld wrote:
> This small series picks up work from Amazon that seems to have stalled
> out later year around this time: listening for the vmgenid ACPI
> notification, and using it to "do something." Last year, that something
> involved a complicated userspace mmap chardev, which seems frought with
> difficulty. This year, I have something much simpler in mind: simply
> using those ACPI notifications to tell the RNG to reinitialize safely,
> so we don't repeat random numbers in cloned, forked, or rolled-back VM
> instances.
>
> This series consists of two patches. The first is a rather
> straightforward addition to random.c, which I feel fine about. The
> second patch is the reason this is just an RFC: it's a cleanup of the
> ACPI driver from last year, and I don't really have much experience
> writing, testing, debugging, or maintaining these types of drivers.
> Ideally this thread would yield somebody saying, "I see the intent of
> this; I'm happy to take over ownership of this part." That way, I can
> focus on the RNG part, and whoever steps up for the paravirt ACPI part
> can focus on that.
>
> As a final note, this series intentionally does _not_ focus on
> notification of these events to userspace or to other kernel consumers.
> Since these VM fork detection events first need to hit the RNG, we can
> later talk about what sorts of notifications or mmap'd counters the RNG
> should be making accessible to elsewhere. But that's a different sort of
> project and ties into a lot of more complicated concerns beyond this
> more basic patchset. So hopefully we can keep the discussion rather
> focused here to this ACPI business.
The main problem with VMGenID is that it is inherently racy. There will
always be a (short) amount of time where the ACPI notification is not
processed, but the VM could use its RNG to for example establish TLS
connections.
Hence we as the next step proposed a multi-stage quiesce/resume
mechanism where the system is aware that it is going into suspend - can
block network connections for example - and only returns to a fully
functional state after an unquiesce phase:
https://github.com/systemd/systemd/issues/20222
Looking at the issue again, it seems like we completely missed to follow
up with a PR to implement that functionality :(.
What exact use case do you have in mind for the RNG/VMGenID update? Can
you think of situations where the race is not an actual concern?
Alex
>
> Cc: dwmw@amazon.co.uk
> Cc: acatan@amazon.com
> Cc: graf@amazon.com
> Cc: colmmacc@amazon.com
> Cc: sblbir@amazon.com
> Cc: raduweis@amazon.com
> Cc: jannh@google.com
> Cc: gregkh@linuxfoundation.org
> Cc: tytso@mit.edu
>
> Jason A. Donenfeld (2):
> random: add mechanism for VM forks to reinitialize crng
> drivers/virt: add vmgenid driver for reinitializing RNG
>
> drivers/char/random.c | 58 ++++++++++++++++++
> drivers/virt/Kconfig | 8 +++
> drivers/virt/Makefile | 1 +
> drivers/virt/vmgenid.c | 133 +++++++++++++++++++++++++++++++++++++++++
> include/linux/random.h | 1 +
> 5 files changed, 201 insertions(+)
> create mode 100644 drivers/virt/vmgenid.c
>
> --
> 2.35.1
>
Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879
next prev parent reply other threads:[~2022-02-24 8:54 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-23 13:12 [PATCH RFC v1 0/2] VM fork detection for RNG Jason A. Donenfeld
2022-02-23 13:12 ` [PATCH RFC v1 1/2] random: add mechanism for VM forks to reinitialize crng Jason A. Donenfeld
2022-02-23 23:16 ` Eric Biggers
2022-02-24 0:54 ` Jason A. Donenfeld
2022-02-24 1:27 ` Eric Biggers
2022-02-24 11:15 ` Jason A. Donenfeld
2022-02-23 13:12 ` [PATCH RFC v1 2/2] drivers/virt: add vmgenid driver for reinitializing RNG Jason A. Donenfeld
2022-02-23 16:36 ` Jason A. Donenfeld
2022-02-23 16:08 ` [PATCH RFC v1 0/2] VM fork detection for RNG Jason A. Donenfeld
2022-02-23 16:19 ` Jason A. Donenfeld
[not found] ` <2653b6c7-a851-7a48-f1f8-3bde742a0c9f@redhat.com>
2022-02-24 10:43 ` Jason A. Donenfeld
2022-02-24 10:55 ` Daniel P. Berrangé
2022-02-24 10:57 ` Jason A. Donenfeld
2022-02-25 10:40 ` Michael S. Tsirkin
2022-02-24 8:53 ` Alexander Graf [this message]
2022-02-24 10:43 ` Daniel P. Berrangé
2022-02-24 11:35 ` Alexander Graf
2022-02-24 10:53 ` Jason A. Donenfeld
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