Re: [RFC PATCH 07/13] powerpc/dexcr: Add sysctl entry for SBHE system override
From: "Nicholas Piggin" <npiggin@gmail.com>
Date: 2023-03-07 05:30:51
Also in:
linux-hardening, lkml
On Mon Nov 28, 2022 at 12:44 PM AEST, Benjamin Gray wrote:
The DEXCR Speculative Branch Hint Enable (SBHE) aspect controls whether the hints provided by BO field of Branch instructions are obeyed during speculative execution. SBHE behaviour per ISA 3.1B: 0: The hints provided by BO field of Branch instructions may be ignored during speculative execution 1: The hints provided by BO field of Branch instructions are obeyed during speculative execution Add a sysctl entry to allow changing this aspect globally in the system at runtime: /proc/sys/kernel/speculative_branch_hint_enable Three values are supported: -1: Disable DEXCR SBHE sysctl override 0: Override and set DEXCR[SBHE] aspect to 0 1: Override and set DEXCR[SBHE] aspect to 1 Internally, introduces a mechanism to apply arbitrary system wide overrides on top of the prctl() config.
Why have an override for this, and not others? Thanks, Nick