CVE-2024-35996

In the Linux kernel, the following vulnerability has been resolved:

cpu: Re-enable CPU mitigations by default for !X86 architectures

Rename x86's to CPU_MITIGATIONS, define it in generic code, and force it

on for all architectures exception x86. A recent commit to turn

mitigations off by default if SPECULATION_MITIGATIONS=n kinda sorta

missed that "cpu_mitigations" is completely generic, whereas

SPECULATION_MITIGATIONS is x86-specific.

Rename x86's SPECULATIVE_MITIGATIONS instead of keeping both and have it

select CPU_MITIGATIONS, as having two configs for the same thing is

unnecessary and confusing. This will also allow x86 to use the knob to

manage mitigations that aren't strictly related to speculative

execution.

Use another Kconfig to communicate to common code that CPU_MITIGATIONS

is already defined instead of having x86's menu depend on the common

CPU_MITIGATIONS. This allows keeping a single point of contact for all

of x86's mitigations, and it's not clear that other architectures *want*

to allow disabling mitigations at compile-time.