linux-hardening - Re: [RFC PATCH 07/13] powerpc/dexcr: Add sysctl entry for SBHE system override

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 07 Mar 2023 15:30:39 +1000
From:   "Nicholas Piggin" <npiggin@...il.com>
To:     "Benjamin Gray" <bgray@...ux.ibm.com>,
        <linuxppc-dev@...ts.ozlabs.org>
Cc:     <ajd@...ux.ibm.com>, <linux-kernel@...r.kernel.org>,
        <linux-hardening@...r.kernel.org>, <cmr@...escreens.de>
Subject: Re: [RFC PATCH 07/13] powerpc/dexcr: Add sysctl entry for SBHE
 system override

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