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

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Date: Wed, 7 Feb 2024 19:28:36 +0100
From: Matthieu Baerts <matttbe@...nel.org>
To: Marco Elver <elver@...gle.com>
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?

Hi Marco,

Thank you for your reply!

On 07/02/2024 19:05, Marco Elver wrote:
> [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.

Thank you for having shared your point of view. I agree with you, the
x86_64_defconfig is probably not the right place.

> 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?
I didn't think about the hardening kconfig. It seems to make sense!

I will wait for people from the Linux Hardening ML to comment if that's
OK :)

Cheers,
Matt
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