[RFC] efi: variable name size limit in efivar_init()

From: Heinrich Schuchardt <xypron.glpk@gmx.de>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-efi <linux-efi@vger.kernel.org>
Subject: [RFC] efi: variable name size limit in efivar_init()
Date: Wed, 17 Mar 2021 08:34:56 +0100	[thread overview]
Message-ID: <75d99346-73c1-993c-8bba-08cb3b3271a2@gmx.de> (raw)

Hello Ard,

in efivar_init() I read:

         /*
          * Per EFI spec, the maximum storage allocated for both
          * the variable name and variable data is 1024 bytes.
          */

         do {
                 variable_name_size = 1024;

This dates back at least to Linux 2.5.0 of 23-Nov-2001 where in
arch/ia64/kernel/efivars.c we have:

/*
  * The maximum size of VariableName + Data = 1024
  * Therefore, it's reasonable to save that much
  * space in each part of the structure,
  * and we use a page for reading/writing.
  */

I cannot find this 1024 byte size limit neither in UEFI spec 2.8B nor in
EFI spec 1.1.

Variable d719b2cb-3d3a-4596-a3bc-dad00e67656f-db has 5080 bytes of data
on my laptop.

It may not reasonable to use a variable name exceeding 512 UTF-16
characters. But shouldn't we handle this case gracefully in efivar_init()?

Best regards

Heinrich