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, 7 Jun 2017 18:26:28 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Daniel Micay <danielmicay@...il.com>
Cc:     Henrique de Moraes Holschuh <hmh@....eng.br>,
        Theodore Ts'o <tytso@....edu>,
        "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 Wed, Jun 07, 2017 at 01:00:25PM -0400, Daniel Micay wrote:
> > 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.

[...]
 
> 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.

I might be missing something here, but the command line is inside of the
device tree, at /chosen/bootargs, so modifying the kernel command line
*is* modifying the device tree in-memory.

For arm64, we have a /chosen/kaslr-seed property that we hope
FW/bootloaders fill in, and similar could be done for some initial
entropy, provided appropriate HW/FW support.

Thanks,
Mark.