From: Eric Biggers <ebiggers@kernel.org>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: 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, dwmw@amazon.co.uk,
acatan@amazon.com, graf@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 1/2] random: add mechanism for VM forks to reinitialize crng
Date: Wed, 23 Feb 2022 17:27:41 -0800 [thread overview]
Message-ID: <YhbfDQ2ernjrRNRX@sol.localdomain> (raw)
In-Reply-To: <CAHmME9oa_wE8_n8e5b=iM5v-s5dgyibm4vXMhwzc8zGd6VWZMQ@mail.gmail.com>
On Thu, Feb 24, 2022 at 01:54:54AM +0100, Jason A. Donenfeld wrote:
> On 2/24/22, Eric Biggers <ebiggers@kernel.org> wrote:
> > I think we should be removing cases where the base_crng key is changed
> > directly
> > besides extraction from the input_pool, not adding new ones. Why not
> > implement
> > this as add_device_randomness() followed by crng_reseed(force=true), where
> > the
> > 'force' argument forces a reseed to occur even if the entropy_count is too
> > low?
>
> Because that induces a "premature next" condition which can let that
> entropy, potentially newly acquired by a storm of IRQs at power-on, be
> bruteforced by unprivileged userspace. I actually had it exactly the
> way you describe at first, but decided that this here is the lesser of
> evils and doesn't really complicate things the way an intentional
> premature next would. The only thing we care about here is branching
> the crng stream, and so this does explicitly that, without having to
> interfere with how we collect entropy. Of course we *also* add it as
> non-credited "device randomness" so that it's part of the next
> reseeding, whenever that might occur.
Can you make sure to properly explain this in the code?
- Eric
next prev parent reply other threads:[~2022-02-24 1:36 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 [this message]
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
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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