linux-kernel - Re: [PATCH] efivarfs: Iterate variables with increasing name buffer sizes

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Message-ID: <CAMj1kXHSSRacU3hp6D3sdUKDESi1FoD33Qi=5Df+=_biZ-vqhA@mail.gmail.com>
Date: Tue, 23 Jan 2024 12:24:11 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Tim Schumacher <timschumi@....de>, Matthew Garrett <mjg59@...f.ucam.org>, 
	Peter Jones <pjones@...hat.com>
Cc: linux-efi@...r.kernel.org, Jeremy Kerr <jk@...abs.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] efivarfs: Iterate variables with increasing name buffer sizes

On Tue, 23 Jan 2024 at 00:15, Tim Schumacher <timschumi@....de> wrote:
>
> This sidesteps a quirk in a few old (2011-ish) UEFI implementations,
> where a call to `GetNextVariableName` with a buffer size larger than 512
> bytes will always return `EFI_INVALID_PARAMETER`.
>
> It is currently unknown whether this is just a botched check or if the
> length is interpreted differently, so the underlying buffer is still
> sized for 1024 bytes, even if we communicate a smaller size to the
> runtime service.
>
> Cc: stable@...r.kernel.org # 6.1+
> Signed-off-by: Tim Schumacher <timschumi@....de>

Hello Tim,

I wonder if we might just reduce this to 512 and be done with it.
Presumably, Windows boots fine in UEFI mode on these machines, which
suggests that it passes a value <= 512 too, and I don't recall ever
encountering systems using extremely long variable names (i.e., longer
than 512 byte)