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Message-ID: <1447152151.29239.0.camel@debian.org>
Date: Tue, 10 Nov 2015 11:42:31 +0100
From: Yves-Alexis Perez <corsac@...ian.org>
To: kernel-hardening@...ts.openwall.com, Matthew Garrett
<mjg59@...f.ucam.org>
Cc: Theodore Tso <tytso@...gle.com>, Emese Revfy <re.emese@...il.com>, Kees
Cook <keescook@...omium.org>, PaX Team <pageexec@...email.hu>, Brad
Spengler <spender@...ecurity.net>, Greg KH <gregkh@...uxfoundation.org>,
Josh Triplett <josh@...htriplett.org>
Subject: Re: Re: Proposal for kernel self protection
features
On lun., 2015-11-09 at 21:13 +0000, Matthew Garrett wrote:
> On Mon, Nov 09, 2015 at 09:09:22PM +0000, Jason Cooper wrote:
>
> > Well, That's why I referred to reading from /boot or from a flash
> > partition. Existing bootloaders in the field already have that
> > capability. That's how they load the kernel.
>
> This doesn't really handle cases like network booting. Most SoCs have
> some kind of RNG, recent x86 has hardware RNG, older x86 frequently has
> an RNG in a TPM. Pulling an entropy seed from the filesystem is a
> reasonable fallback, but we should definitely be thinking of it as a
> fallback - someone with physical access to your system while it's turned
> off may be able to infer the ASLR state for your next boot, for
> instance.
About the TPM RNG: I was definitely interested in the “get entropy from
TPM” kind of thing for my laptop (even though I think my laptop would
not be the worst place to find entropy). Right now I'm using rng-tools
to read from /dev/hwrng (handled by tpm_rng module), which then feeds
entropy to /dev/random (or maybe directly using the RND ioctls).
Do you think bypassing userland completely in order to be able to feed
that entropy even before userland is completely initialized would be
helpful?
Regards,
--
Yves-Alexis
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