Received-SPF: pass (google.com: best guess record for domain of linux-ext4-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
To:     "Ahmed S. Darwish" <darwish.07@gmail.com>,
        Theodore Ts'o <tytso@mit.edu>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Jan Kara <jack@suse.cz>, zhangjs <zachary@baishancloud.com>,
        linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20190910042107.GA1517@darwi-home-pc>
From:   Jon Masters <jcm@jonmasters.org>
Message-ID: <60fc1d03-314a-6b0a-2c8f-100394b05969@jonmasters.org>
Date:   Thu, 3 Oct 2019 17:10:45 -0400
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.4.0
MIME-Version: 1.0
In-Reply-To: <20190910042107.GA1517@darwi-home-pc>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Subject: Re: Linux 5.3-rc8
Sender: linux-ext4-owner@vger.kernel.org
Precedence: bulk

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.