Message-ID: <1496894341.10825.26.camel@gmail.com>
Subject: Re: [kernel-hardening] Re: [PATCH v3 04/13] crypto/rng: ensure that
 the RNG is ready before using
From: Daniel Micay <danielmicay@gmail.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Henrique de Moraes Holschuh <hmh@hmh.eng.br>,
        "Theodore Ts'o" <tytso@mit.edu>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Eric Biggers <ebiggers3@gmail.com>,
        Linux Crypto Mailing List <linux-crypto@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        kernel-hardening@lists.openwall.com,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        David Miller <davem@davemloft.net>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        Stephan Mueller <smueller@chronox.de>
Date: Wed, 07 Jun 2017 23:59:01 -0400
In-Reply-To: <20170607172627.GB8330@leverpostej>
References: <20170606005108.5646-1-Jason@zx2c4.com>
         <20170606005108.5646-5-Jason@zx2c4.com>
         <20170606030004.4go6btmobrsmqiwz@thunk.org>
         <CAHmME9qZUEMDjQGNOBC7PrCTcanOxohVHcED+Xyg_3jR64Q7VQ@mail.gmail.com>
         <20170606044404.GA3469@zzz>
         <CAHmME9q0N3KgWU4XMDmzNjd0EF_HWROBquwXMYXxfssx_VoghA@mail.gmail.com>
         <20170606170319.5eva2yoxxeru5p74@thunk.org>
         <20170606221910.GB9057@khazad-dum.debian.net>
         <1496854825.10825.24.camel@gmail.com> <20170607172627.GB8330@leverpostej>
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On Wed, 2017-06-07 at 18:26 +0100, Mark Rutland wrote:
> 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.

I was assuming it was simpler since bootloaders are already setting it,
but it seems I'm wrong about that.