linux-kernel - Re: Linux 5.3-rc8

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Message-ID: <CAHk-=whYhC-qXHdEypy6iC7SzPA+KvWphLXSGF+mvGCGHGjNZw@mail.gmail.com>
Date:   Wed, 18 Sep 2019 13:26:39 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Alexander E. Patrakov" <patrakov@...il.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Lennart Poettering <mzxreary@...inter.de>,
        "Ahmed S. Darwish" <darwish.07@...il.com>,
        "Theodore Y. Ts'o" <tytso@....edu>, Willy Tarreau <w@....eu>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Vito Caputo <vcaputo@...garu.com>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.cz>, Ray Strode <rstrode@...hat.com>,
        William Jon McCann <mccann@....edu>,
        zhangjs <zachary@...shancloud.com>, linux-ext4@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: Linux 5.3-rc8

On Wed, Sep 18, 2019 at 1:15 PM Alexander E. Patrakov
<patrakov@...il.com> wrote:
>
> No, this is not the solution, if we take seriously not only getrandom
> hangs, but also urandom warnings. In some setups (root on LUKS is one of
> them) they happen early in the initramfs. Therefore "restoring" entropy
> from the previous boot by a script that runs from the main system is too
> late. That's why it is suggested to load at least a part of the random
> seed in the boot loader, and that has not been commonly implemented.

Honestly, I think the bootloader suggestion is naive and silly too.

Yes, we now support it. And no, I don't think people will trust that
either. And I suspect for good reason: there's really very little
reason to believe that bootloaders would be any better than any other
part of the system.

So right now some people trust bootloaders exactly _because_ there
basically is just one or two that do this, and the people who use them
are usually the people who wrote them or are at least closely
associated with them. That will change, and then people will say "why
would I trust that, when we know of bug Xyz".

And I guarantee that those bugs _will_ happen, and people will quite
reasonably then say "yeah, I don't trust the bootloader". Bootloaders
do some questionable things.

The most likely thing to actually be somewhat useful is I feel things
like the kernel just saving the seed by itself in nvram. There's
already an example of this for the EFI random seed thing, but that's
used purely for kexec, I think.

Adding an EFI variable (or other platform nonvolatile thing), and
reading (and writing to it) purely from the kernel ends up being one
of those things where you can then say "ok, if we trust the platform
AT ALL, we can trust that". Since you can't reasonably do things like
add EFI variables to your distro image by mistake.

Of course, even then people will say "I don't trust the platform". But
at some point you just say "you have trust issues" and move on.

            Linus