[bug #66603] grub_crypto_memcmp side-channel

Mostafa Amin <[email protected]> Fri, 2 May 2025 09:49:08 -0400 (EDT)

Newsgroups	gmane.comp.boot-loaders.grub.bugs
Message-ID	<[email protected]>

Follow-up Comment #3, bug #66603 (group grub):

Hi Vladimir and others,

Checking in on this bug (#66603) as it relates to CVE-2024-56738, which is
still affecting current Debian releases (tracked in Debian bug #1102217:
https://bugs.debian.org/1102217) .

I see Vladimir Serbinenko mentioned back in December 2024 (comment #2) a plan
to switch to using libgcrypt functions after updating libgcrypt. Has there
been any progress on that front, or is there an estimated timeline?

In the meantime, the constant-time comparison fix proposed by Jonathan Bar Or
in the original report (or a similar patch, like the one I have tested based
on the same principle) seems like a viable solution to address the immediate
side-channel vulnerability.

Would applying such a direct fix be acceptable for GRUB in the interim, or is
the switch to libgcrypt the only path forward?

I have a tested patch implementing the constant-time comparison using bitwise
operations (similar to the one attached here previously) that resolves the
issue on Debian systems. Happy to provide it again if helpful.

Thanks,
Mostafa


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