linux-kernel - Re: [kernel-hardening] Re: [PATCH v3 04/13] crypto/rng: ensure that the RNG is ready before using

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Date:   Wed, 07 Jun 2017 13:00:25 -0400
From:   Daniel Micay <danielmicay@...il.com>
To:     Henrique de Moraes Holschuh <hmh@....eng.br>,
        Theodore Ts'o <tytso@....edu>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Eric Biggers <ebiggers3@...il.com>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-hardening@...ts.openwall.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Miller <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Stephan Mueller <smueller@...onox.de>
Subject: Re: [kernel-hardening] Re: [PATCH v3 04/13] crypto/rng: ensure that
 the RNG is ready before using

> On the better bootloaders, an initramfs segment can be loaded
> independently (and you can have as many as required), which makes an
> early_initramfs a more palatable vector to inject large amounts of
> entropy into the next boot than, say, modifying the kernel image
> directly at every boot/shutdown to stash entropy in there somewhere.

Modifying the kernel image on storage isn't compatible with verified
boot so it's not really a solution. The kernel, initrd and rest of the
OS are signed and verified on operating systems like Android, Android
Things, ChromeOS and many embedded devices, etc. putting some basic
effort into security. I didn't really understand the device tree
approach and mentioned a few times before. Passing via the kernel
cmdline is a lot simpler than modifying the device tree in-memory and
persistent modification isn't an option unless verified boot is missing
anyway.