linux-kernel - Re: [PATCH 0/4] efi: verify that variable services are supported

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Date:   Mon, 23 Jan 2023 13:06:06 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Johan Hovold <johan+linaro@...nel.org>
Cc:     Matthew Garrett <mjg59@...f.ucam.org>, Jeremy Kerr <jk@...abs.org>,
        Maximilian Luz <luzmaximilian@...il.com>,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] efi: verify that variable services are supported

On Thu, 19 Jan 2023 at 17:45, Johan Hovold <johan+linaro@...nel.org> wrote:
>
> This series adds a sanity check to make sure that the variable services
> are actually available before registering the generic efivar ops.
>
> This is used to address some potential races with custom efivars
> implementation such as the Google SMI or upcoming Qualcomm SCM ones.
>
> Specifically, efivarfs currently requires that the efivar ops have been
> registered before module init time even though the Google driver can be
> built as a module. Instead, the driver has so far relied on the fact
> that the generic ops have been registered by efi core only to later be
> overridden by the custom implementation (or Google doesn't use
> efivarfs).
>
> Instead, let's move the efivars sanity check to mount time to allow for
> late registration of efivars.
>
> Note that requiring that all efivars implementation to always be
> built-in and registered before module init time could be an alternative,
> but we'd still need to make sure that the custom implementation is then
> not overridden by the default (broken) one. To avoid such init call
> games, allowing late registration seems preferable.
>
> This would however require any drivers that use efivars to probe defer
> until it becomes available, which is also unfortunate, but possibly
> still better than having generic kernels carry multiple built-in efivars
> implementations.
>
> Note that there are currently no such (efivars consumer) drivers in-tree
> except for the efivars_pstore driver, which currently do rely on
> efivarfs being available at module init time (and hence may fail to
> initialise with the custom efivar implementations).
>
> Johan
>
>
> Johan Hovold (4):
>   efi: efivars: add efivars printk prefix
>   efivarfs: always register filesystem
>   efi: verify that variable services are supported
>   efi: efivars: prevent double registration
>

Queued up in efi/next - thanks.

>  drivers/firmware/efi/efi.c  | 22 ++++++++++++++++++++++
>  drivers/firmware/efi/vars.c | 17 ++++++++++++++---
>  fs/efivarfs/super.c         |  6 +++---
>  3 files changed, 39 insertions(+), 6 deletions(-)
>
> --
> 2.38.2
>