linux-kernel - Re: [PATCH] seqlock: Allow UBSAN to fail optimizing

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Message-ID: <aX5NG2aOyvTXU6qZ@outflux.net>
Date: Sat, 31 Jan 2026 10:42:35 -0800
From: Kees Cook <kees@...ian.org>
To: Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org, oleg@...hat.com,
        linux-kernel@...r.kernel.org, debian-kernel@...ts.debian.org,
        kees@...nel.org
Subject: Re: [PATCH] seqlock: Allow UBSAN to fail optimizing

On Sat, Jan 31, 2026 at 10:39:42AM +0100, Salvatore Bonaccorso wrote:
> Kees, Peter approached the Debian kernel list above to drop
> CONFIG_UBSAN again, which, so I think we need to revert your
> 6cfadabfe015 ("Enable UBSAN_BOUNDS and UBSAN_SHIFT"):
> https://salsa.debian.org/kernel-team/linux/-/commit/6cfadabfe015fa0d659fc8e3efd495cbcae3e44e
> 
> I have make a MR for our packaging for the change in
> https://salsa.debian.org/kernel-team/linux/-/merge_requests/1804

I am strongly opposed -- this undoes years of security flaw mitigation
work and leaves Debian (and only Debian!) exposed to trivial array index
overflows. The bounds sanitizer is the corner stone of memory safety
for C, and is not some "experimental" feature. GCC has a long history
of trouble with inlining, so this is not something unique to enabling
this feature.

I replied similarly to the PR. This would be a major mistake to disable.

-Kees

-- 
Kees Cook                                            @debian.org