linux-kernel - Re: [RFC PATCH 0/2] Enhancing Boot Speed and Security with Delayed Module Signature Verification

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Date:   Wed, 8 Nov 2023 10:32:13 -0500
From:   Prarit Bhargava <prarit@...hat.com>
To:     "Alessandro Carminati (Red Hat)" <alessandro.carminati@...il.com>,
        linux-modules@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Luis Chamberlain <mcgrof@...nel.org>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org
Subject: Re: [RFC PATCH 0/2] Enhancing Boot Speed and Security with Delayed
 Module Signature Verification

On 9/14/23 07:27, Alessandro Carminati (Red Hat) wrote:
> This patch sets up a new feature to the Linux kernel to have the ability,
> while module signature checking is enabled, to delay the moment where
> these signatures are effectively checked. The feature is structure into
> two main key points, the feature can be enabled by a new command line
> kernel argument, while in delay mode, the kernel waits until the
> userspace communicates to start checking signature modules.
> This operation can be done by writing a value in a securityfs file,
> which works the same as /sys/kernel/security/lockdown.
> 
> Patch 1/2: Modules: Introduce boot-time module signature flexibility
> The first patch in this set fundamentally alters the kernel's behavior
> at boot time by implementing a delayed module signature verification
> mechanism. It introduces a new boot-time kernel argument that allows
> users to request this delay. By doing so, we aim to capitalize on the
> cryptographic checks already performed on the kernel and initrd images
> during the secure boot process. As a result, we can significantly
> improve the boot speed without compromising system security.
> 
> Patch 2/2: docs: Update kernel-parameters.txt for signature verification
> enhancement
> The second patch is just to update the kernel parameters list
> documentation.
> 
> Background and Motivation
> In certain contexts, boot speed becomes crucial. This patch follows the
> recognition that security checks can at times be redundant. Therefore,
> it proves valuable to skip those checks that have already been validated.
> 
> In a typical Secure Boot startup with an initrd, the bootloader is
> responsible for verifying artifacts before relinquishing control. In a
> verified initrd image, it is reasonable to assume that its content is
> also secure. Consequently, verifying module signatures may be deemed
> unnecessary.
> This patch introduces a feature to skip signature verification during
> the initrd boot phase.
> 

I think this is fine to do.  There is some risk for users who may use 
this without realizing what they're actually doing and then would end up 
creating a security hole.  But there are far worse ways you can do that 
with access to kernel paramaters.

P.

> Alessandro Carminati (Red Hat) (2):
>    Modules: Introduce boot-time module signature flexibility
>    docs: Update kernel-parameters.txt for signature verification
>      enhancement
> 
>   .../admin-guide/kernel-parameters.txt         |  9 +++
>   include/linux/module.h                        |  4 ++
>   kernel/module/main.c                          | 14 +++--
>   kernel/module/signing.c                       | 56 +++++++++++++++++++
>   4 files changed, 77 insertions(+), 6 deletions(-)
>