linux-kernel - Re: [PATCH v3 1/5] efi: vars: prohibit reading random seed variables

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Message-ID: <20221127210040.GA32253@srcf.ucam.org>
Date:   Sun, 27 Nov 2022 21:00:40 +0000
From:   Matthew Garrett <mjg59@...f.ucam.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux-efi@...r.kernel.org, linux-crypto@...r.kernel.org,
        patches@...ts.linux.dev, linux-kernel@...r.kernel.org,
        ardb@...nel.org
Subject: Re: [PATCH v3 1/5] efi: vars: prohibit reading random seed variables

On Tue, Nov 22, 2022 at 03:04:00AM +0100, Jason A. Donenfeld wrote:
> In anticipation of putting random seeds in EFI variables, it's important
> that the random GUID namespace of variables remains hidden from
> userspace. We accomplish this by not populating efivarfs with entries
> from that GUID, as well as denying the creation of new ones in that
> GUID.

What's the concern here? Booting an older kernel would allow a malicious 
actor to either read the seed variable or set it to a value under their 
control, so we can't guarantee that the information is secret.