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Date: Tue, 10 Nov 2015 11:47:47 +0100
From: Marcus Meissner <>
Cc: Matthew Garrett <>, Theodore Tso <>,
	Emese Revfy <>, Kees Cook <>,
	PaX Team <>,
	Brad Spengler <>,
	Greg KH <>,
	Josh Triplett <>
Subject: Re: Re: Proposal for kernel self protection

On Tue, Nov 10, 2015 at 11:42:31AM +0100, Yves-Alexis Perez wrote:
> 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?

The kernel has infrastructure for this (feeding hardware random generators
into the random pool) these days.


How "good" the generator is is determined by  the "quality" member of
the hwrng struct.

(It seems only virtio-rng.c sets one, but more of them could be reviewed
and used.)

Ciao, Marcus

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