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

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Message-ID: <CANpmjNP==CANQi4_qFV_VVFDMsj1wHROxt3RKzwJBqo8_McCTg@mail.gmail.com>
Date: Wed, 7 Feb 2024 19:05:31 +0100
From: Marco Elver <elver@...gle.com>
To: Matthieu Baerts <matttbe@...nel.org>
Cc: Alexander Potapenko <glider@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, kasan-dev@...glegroups.com, 
	Netdev <netdev@...r.kernel.org>, Jakub Kicinski <kuba@...nel.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?

[Cc'ing a bunch more people to get input]

Hi Matt,

On Wed, 7 Feb 2024 at 17:16, Matthieu Baerts <matttbe@...nel.org> wrote:
[...]
> When talking to Jakub about the kernel config used by the new CI for the
> net tree [1], Jakub suggested [2] to check if KFENCE could not be
> enabled by default for x86 architecture.
>
> As KFENCE maintainers, what do you think about that? Do you see some
> blocking points? Do you plan to add it in x86_64_defconfig?

We have no concrete plans to add it to x86 defconfig. I don't think
there'd be anything wrong with that from a technical point of view,
but I think defconfig should remain relatively minimal.

I guess different groups of people will disagree here: as kernel
maintainers, it'd be a good thing because we get more coverage and
higher probability of catching memory-safety bugs; as a user, I think
having defconfig enable KFENCE seems unintuitive.

I think this would belong into some "hardening" config - while KFENCE
is not a mitigation (due to sampling) it has the performance
characteristics of unintrusive hardening techniques, so I think it
would be a good fit. I think that'd be
"kernel/configs/hardening.config".

Preferences?

Thanks,
-- Marco