linux-hardening - Re: KFENCE: included in x86 defconfig?

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Date: Thu, 8 Feb 2024 11:11:48 +0000
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Borislav Petkov <bp@...en8.de>
Cc: Marco Elver <elver@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Matthieu Baerts <matttbe@...nel.org>, Alexander Potapenko <glider@...gle.com>, 
	Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com, 
	Netdev <netdev@...r.kernel.org>, linux-hardening@...r.kernel.org, 
	Kees Cook <keescook@...omium.org>, "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: KFENCE: included in x86 defconfig?

On Thu, 8 Feb 2024 at 10:55, Borislav Petkov <bp@...en8.de> wrote:
>
> What about its benefit?
>
> I haven't seen a bug fix saying "found by KFENCE" or so but that doesn't
> mean a whole lot.

It does find some things. You can search for "BUG: KFENCE" on lore,
and there are real bug reports.

That said, there are real downsides too. Yes, you potentially find
bugs, but the act of finding the bugs might also cause issues. And
that means that anybody who enables KFENCE then needs to be willing to
deal with said issues and have the infrastructure to debug and report
them upstream.

I think that's the *real* cost there - KFENCE is likely a good idea,
but I'm not convinced it should be a defconfig thing, it should be a
conscious decision.

           Linus