Re: [PATCH v2 1/2] arch/Kconfig: Make CONFIG_CPU_SPECTRE available for all architectures

[Pawan Gupta]

On 28.10.2021 14:49, Mark Rutland wrote:
> On Wed, Oct 27, 2021 at 06:33:22PM -0700, Pawan Gupta wrote:
> > Borrow CONFIG_CPU_SPECTRE from ARM to be available for all
> > architectures. This will help in configuration of features that depend
> > on CPU being affected by spectre class of vulnerabilities.
> >
> > Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
>
> Given that spectre isn't one specific issue, biut rather a blanket term
> for a bunch of things that can have variable overlap, I don't think this
> makes much sense unless we're going to add finer-grained options for all
> the variants, and IMO it'd make more sene for the architectures to
> directly select the things that'd otherwise be dependent on this.

Isn't ARM already using CPU_SPECTRE for selecting things: 

	config HARDEN_BRANCH_PREDICTOR
	     bool "Harden the branch predictor against aliasing attacks" if EXPERT
	     depends on CPU_SPECTRE

This was the whole motivation for doing the same for x86.

Adding a condition for all architectures is also okay, but its going to
a little messier:

	 config BPF_UNPRIV_DEFAULT_OFF
	        default y if X86 || ARM || ... 

This approach would make sense if architectures wants to explicitly
select the defaults irrespective of architecture being affected by
spectre.

If that's the case I will change the BPF_UNPRIV_DEFAULT_OFF default to
depend on architecture. I hope BPF maintainer, Daniel is okay with it?

Pawan

Added BPF maintainers and bpf@vger to cc.