linux-kernel - Re: [PATCH 8/8] efi: pstore: Add module parameter for setting the record size

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Message-ID: <202210061614.8AA746094A@keescook>
Date:   Thu, 6 Oct 2022 16:16:16 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        kernel-dev@...lia.com, kernel@...ccoli.net, anton@...msg.org,
        ccross@...roid.com, tony.luck@...el.com, linux-efi@...r.kernel.org,
        Ard Biesheuvel <ardb@...nel.org>
Subject: Re: [PATCH 8/8] efi: pstore: Add module parameter for setting the
 record size

On Thu, Oct 06, 2022 at 07:42:12PM -0300, Guilherme G. Piccoli wrote:
> By default, the efi-pstore backend hardcode the UEFI variable size
> as 1024 bytes. That's not a big deal, but at the same time having
> no way to change that in the kernel is a bit bummer for specialized
> users - there is not such a limit in the UEFI specification.

It seems to have been added in commit
e0d59733f6b1 ("efivars, efi-pstore: Hold off deletion of sysfs entry until the scan is completed")

But I see no mention of why it was introduced or how it was chosen.

I remember hearing some horror stories from Matthew Garrett about older
EFI implementations bricking themselves when they stored large
variables, or something like that, but I don't know if that's meaningful
here at all.

I think it'd be great to make it configurable! Ard, do you have any
sense of what the max/min, etc, should be here?

-- 
Kees Cook