On 29.10.2021 11:08, Russell King (Oracle) wrote:

On Thu, Oct 28, 2021 at 12:36:58PM -0700, Pawan Gupta wrote:

quoted

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 || ...

It doesn't have to be (but sadly we end up repeating "DEFAULT"):

config BPF_UNPRIV_DEFAULT_OFF_DEFAULT
bool

config BPF_UNPRIV_DEFAULT_OFF
bool "Disable unprivileged BPF by default"
default BPF_UNPRIV_DEFAULT_OFF_DEFAULT

Then architectures can select BPF_UNPRIV_DEFAULT_OFF_DEFAULT if they
wish this to be defaulted to "yes".

Looks like we are settling on unconditional 'default y' for now [1].
I have sent a v3 with 'default y' [2].

However, please note that this has limited use given that the
BPF_UNPRIV_DEFAULT_OFF option has been around for a while now. Any
existing configuration that mentions this symbol will override any
default specified in the Kconfig files if the option is user-visible.

Yes, existing configurations will have to toggle this manually. However,
many distros already have BPF_UNPRIV_DEFAULT_OFF=y in their
configuration.

So, IMHO, defaults need to be set correctly from the point in time
that the option is introduced.

Agree.

[1] https://lore.kernel.org/lkml/6130e55f-4d84-5ada-4e86-5b678e3eaf5e@iogearbox.net/ (local)
[2] https://lore.kernel.org/lkml/0ace9ce3f97656d5f62d11093ad7ee81190c3c25.1635535215.git.pawan.kumar.gupta@linux.intel.com/ (local)

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