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Re: [RFC PATCH] kern/dl: Add module version check

From: Zhang Boyang
Subject: Re: [RFC PATCH] kern/dl: Add module version check
Date: Wed, 21 Dec 2022 15:57:08 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.6.0


(sorry for duplicate emails because I forgot to add CCs)

On 2022/12/21 06:58, Robbie Harwood wrote:
Zhang Boyang <> writes:

This patch add version information to GRUB modules. Specifically,
PACKAGE_VERSION is embedded as null-terminated string in .modver
section. This string is checked at module loading time. That module will
be rejected if mismatch is found. This will prevent loading modules from
different versions of GRUB.

It should be pointed out that the version string is only consisted of
PACKAGE_VERSION. Any difference not reflected in PACKAGE_VERSION is not
noticed by version check (e.g. configure options).

Right now, this only affects non-secureboot scenarios (because we don't
have external signed module support).  I would want to see a resolution
to the external module signing question first so that we don't paint
ourselves into a corner with something like this.

This feature is a prerequisite for external signed module support (and it is mainly designed for this purpose). SBAT itself is not sufficient to protect version mismatch attacks. Consider this scenario:

1) GRUB 2.XX is free of vulnerabilities

2) GRUB 2.YY is also free of vulnerabilities

3) So GRUB 2.XX shares same SBAT numbers with GRUB 2.YY

4) So if there is no version check, it's possible to load GRUB 2.YY modules into GRUB 2.XX (and vice versa)

5) However, due to some changes in API or ABI, there is possibility that there are vulnerabilities when using GRUB 2.YY modules with GRUB 2.XX.

I share Glenn's confusion about what real-world problems this addresses:
my understanding is that grub modules mostly register callbacks, so the
possibility of disaster is low (unless the callback interfaces change of
course, but that generally has not happened).

Please see my reply to Glenn for a example that mismatched modules crashes GRUB.

The combination of those two things leads me to suspect this is not the
right approach.  It seems likely that if we want to down the road of
versionlocking, something like the kernel's ephemeral key approach would
be better suited - and if we want external modules (which I don't think
we do), full SBAT support.

Sorry but I'm not familiar with the kernel's ephemeral key approach. Could you please give me some links to this?

By the way, I figured out why shim doesn't enforce SBAT checks for files if they are not directly loaded by shim AND have no SBAT information. According to , it's vendor's responsibility to revoke all files without SBAT information and only sign files with SBAT information at all time.

My grub-wrap patch ( ) already has support for embedding SBAT information to PE wrappers, although it not enforced. With this patch, it should be easy to implement external modules if wanted (yes, with full SBAT support, if vendor always add SBAT information to modules).

Best Regards,
Zhang Boyang

Be well,

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