linux-kernel - Re: Linux 5.3-rc8

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Message-ID: <cbcfca99-5c84-bab5-3b50-448e048bd2e9@jonmasters.org>
Date:   Thu, 3 Oct 2019 17:31:43 -0400
From:   Jon Masters <jcm@...masters.org>
To:     "Ahmed S. Darwish" <darwish.07@...il.com>,
        Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Jan Kara <jack@...e.cz>, zhangjs <zachary@...shancloud.com>,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Linux 5.3-rc8

On 9/10/19 12:21 AM, Ahmed S. Darwish wrote:

> Can this even be considered a user-space breakage? I'm honestly not
> sure. On my modern RDRAND-capable x86, just running rng-tools rngd(8)
> early-on fixes the problem. I'm not sure about the status of older
> CPUs though.

Tangent: I asked aloud on Twitter last night if anyone had exploited
Rowhammer-like effects to generate entropy...and sure enough, the usual
suspects have: https://arxiv.org/pdf/1808.04286.pdf

While this requires low level access to a memory controller, it's
perhaps an example of something a platform designer could look at as a
source to introduce boot-time entropy for e.g. EFI_RNG_PROTOCOL even on
an existing platform without dedicated hardware for the purpose.

Just a thought.

Jon.